How can I test if a value is repeated in array? - perl

I'm doing a subroutine that takes a list of numbers as an argument. What I would like to do is check if there is a repeated value in that list. In case there are repeated numbers, print a message and stop the program. In case there are no repeated numbers, continue with the execution.
For example:
if (there_is_number_repeated){
print "There is a number repeated";}
else{
run this code...}
I was trying to do this creating a hash with the values of that list, and then check if there are values > 1.
use strict;
use warnings;
sub name_subroutine{
my (#numbers)=#_;
my $n=scalar(#numbers);
my %table=();
foreach my $i(#numbers){
if (exists $tabla{$i}){
$tabla{$i}+=1;}
else{
$tabla{$i} = 1;
}
my #values = values %tabla;
}
}
It's here where I do not know to continue. Is there any way to do this in an amateurish way? I'm newbie in Perl.
Thanks!

I would just do:
my %uniq;
if ( grep ++$uniq{$_} > 1, #numbers ) {
# some numbers are repeated
}
In your existing code (with a couple corrections):
my %table=();
foreach my $i(#numbers){
if (exists $table{$i}){
$table{$i}+=1;}
else{
$table{$i} = 1;
}
}
my #values = values %table;
you don't need to check for exists; doing += 1 or ++ will set it to 1 if it didn't exist. And you don't want the values (those are just the counts of how many times each array value was found), you want the keys, specifically those for which the value is > 1:
my #repeated = grep $table{$_} > 1, keys %table;

my #arr = #_;
my $count = #arr;
for(my $i=0;$i<$count;$i++)
{
my $num = $arr[$i];
for(my $j=0; $j<$count,$j!=$i; $j++)
{
if($num == $arr[$j])
{
print "\n$num is repeated";
last;
}
}
}
Tried and tested. Cheers.

Related

Subkey comparison function for sorting

I need a Perl comparison function that can be used with sort.
Each key is a text string that has an arbitrary number of subkeys, separated by delimiter characters (dot, colon, space, and slash). Some subkeys are numeric, and need to be sorted numerically. The key format and number of subkeys varies. Therefore, the comparison has to handle one key being longer than the other, and has to handle the case where a subkey is numeric in one key but not in another (in which case a textual comparison is appropriate for that subkey).
This works, but I bet there are better solutions:
use warnings;
use strict;
use Scalar::Util qw[looks_like_number];
sub hier_cmp {
my $aa = $a;
my $bb = $b;
# convert all delims (. : / space) to the same delim
$aa =~ tr/.:\/ /::::/;
$bb =~ tr/.:\/ /::::/;
my #lista = split(":", $aa);
my #listb = split(":", $bb);
my $result;
for my $ix (0 .. min($#lista, $#listb)) {
if (exists($lista[$ix]) && exists($listb[$ix])) {
if ( looks_like_number($lista[$ix]) && looks_like_number($listb[$ix])) {
# compare numerically
$result = ($lista[$ix] <=> $listb[$ix]);
} else {
# compare as strings
$result = ($lista[$ix] cmp $listb[$ix]);
}
if ($result == 0) {
next;
}
return $result;
} elsif (exists($lista[$ix])) {
return 1;
} else {
return -1;
}
}
}
For my purposes, readability is more important than speed. This is just for an internal tool, and lists will rarely have more than hundreds of elements. However, any opportunity to learn something is good.
As you can see, I'm not a perl wizard. Even trivial improvements on my code would be appreciated.
Thanks!
That looks like natural sorting. There are several modules on CPAN that already do that such as Sort::Naturally or Sort::Key::Natural.
For instance:
use Sort::Key::Natural qw(natsort);
my #sorted = natsort #data;
It would help if you gave us some data to test with, but this code passes a few basic tests and it looks right.
It simplifies the problem by using the List::MoreUtils function pairwise to create an array of field pairs.
Then it is just a matter of checking whether only one is defined, when one of the lists has come to an end before the other and should be sorted first; if they are both numeric, when they should be compared with a numeric comparison; or otherwise simply compare them as strings.
If the end of the array of pairs is reached then everything has matched and zero is returned to indicate equiality.
Update
I have changed this code to remove the dependency on List::MoreUtils::pairwise.
use strict;
use warnings;
use Scalar::Util 'looks_like_number';
sub hier_cmp {
our ($a, $b);
my #a = split m|[.: /]+|, $a;
my #b = split m|[.: /]+|, $b;
for my $i (0 .. $#a > $#b ? $#a : $#b) {
my #ab = ( $a[$i], $b[$i] );
if (grep defined, #ab < 2) {
return defined $ab[0] ? 1 : -1;
}
else {
my $numeric = grep(looks_like_number($_), #ab) == 2;
my $result = $numeric ? $ab[0] <=> $ab[1] : $ab[0] cmp $ab[1];
return $result if $result;
}
}
return 0;
}

Find the word with most letters in common with other words

I want Perl (5.8.8) to find out what word has the most letters in common with the other words in an array - but only letters that are in the same place. (And preferably without using libs.)
Take this list of words as an example:
BAKER
SALER
BALER
CARER
RUFFR
Her BALER is the word that has the most letters in common with the others. It matches BAxER in BAKER, xALER in SALER, xAxER in CARER, and xxxxR in RUFFR.
I want Perl to find this word for me in an arbitrary list of words with the same length and case. Seems I've hit the wall here, so help is much appreciated!
What I've tried until now
Don't really have much of a script at the moment:
use strict;
use warnings;
my #wordlist = qw(BAKER SALER MALER BARER RUFFR);
foreach my $word (#wordlist) {
my #letters = split(//, $word);
# now trip trough each iteration and work magic...
}
Where the comment is, I've tried several kinds of code, heavy with for-loops and ++ varables. Thus far, none of my attempts have done what I need it to do.
So, to better explain: What I need is to test word for word against the list, for each letterposition, to find the word that has the most letters in common with the others in the list, at that letter's position.
One possible way could be to first check which word(s) has the most in common at letter-position 0, then test letter-position 1, and so on, until you find the word that in sum has the most letters in common with the other words in the list. Then I'd like to print the list like a matrix with scores for each letterposition plus a total score for each word, not unlike what DavidO suggest.
What you'd in effect end up with is a matrix for each words, with the score for each letter position, and the sum total score fore each word in the matrix.
Purpose of the Program
Hehe, I might as well say it: The program is for hacking terminals in the game Fallout 3. :D My thinking is that it's a great way to learn Perl while also having fun gaming.
Here's one of the Fallout 3 terminal hacking tutorials I've used for research: FALLOUT 3: Hacking FAQ v1.2, and I've already made a program to shorten the list of words, like this:
#!/usr/bin/perl
# See if one word has equal letters as the other, and how many of them are equal
use strict;
use warnings;
my $checkword = "APPRECIATION"; # the word to be checked
my $match = 4; # equal to the match you got from testing your checkword
my #checkletters = split(//, $checkword); #/
my #wordlist = qw(
PARTNERSHIPS
REPRIMANDING
CIVILIZATION
APPRECIATION
CONVERSATION
CIRCUMSTANCE
PURIFICATION
SECLUSIONIST
CONSTRUCTION
DISAPPEARING
TRANSMISSION
APPREHENSIVE
ENCOUNTERING
);
print "$checkword has $match letters in common with:\n";
foreach my $word (#wordlist) {
next if $word eq $checkword;
my #letters = split(//, $word);
my $length = #letters; # determine length of array (how many letters to check)
my $eq_letters = 0; # reset to 0 for every new word to be tested
for (my $i = 0; $i < $length; $i++) {
if ($letters[$i] eq $checkletters[$i]) {
$eq_letters++;
}
}
if ($eq_letters == $match) {
print "$word\n";
}
}
# Now to make a script on to find the best word to check in the first place...
This script will yield CONSTRUCTION and TRANSMISSION as its result, just as in the game FAQ. The trick to the original question, though (and the thing I didn't manage to find out on my own), is how to find the best word to try in the first place, i.e. APPRECIATION.
OK, I've now supplied my own solution based on your help, and consider this thread closed. Many, many thanks to all the contributers. You've helped tremendously, and on the way I've also learned a lot. :D
Here's one way. Having re-read your spec a couple of times I think it's what you're looking for.
It's worth mentioning that it's possible there will be more than one word with an equal top score. From your list there's only one winner, but it's possible that in longer lists, there will be several equally winning words. This solution deals with that. Also, as I understand it, you count letter matches only if they occur in the same column per word. If that's the case, here's a working solution:
use 5.012;
use strict;
use warnings;
use List::Util 'max';
my #words = qw/
BAKER
SALER
BALER
CARER
RUFFR
/;
my #scores;
foreach my $word ( #words ) {
my $score;
foreach my $comp_word ( #words ) {
next if $comp_word eq $word;
foreach my $pos ( 0 .. ( length $word ) - 1 ) {
$score++ if substr( $word, $pos, 1 ) eq substr( $comp_word, $pos, 1);
}
}
push #scores, $score;
}
my $max = max( #scores );
my ( #max_ixs ) = grep { $scores[$_] == $max } 0 .. $#scores;
say "Words with most matches:";
say for #words[#max_ixs];
This solution counts how many times per letter column each word's letters match other words. So for example:
Words: Scores: Because:
ABC 1, 2, 1 = 4 A matched once, B matched twice, C matched once.
ABD 1, 2, 1 = 4 A matched once, B matched twice, D matched once.
CBD 0, 2, 1 = 3 C never matched, B matched twice, D matched once.
BAC 0, 0, 1 = 1 B never matched, A never matched, C matched once.
That gives you the winners of ABC and ABD, each with a score of four positional matches. Ie, the cumulative times that column one, row one matched column one row two, three, and four, and so on for the subsequent columns.
It may be able to be optimized further, and re-worded to be shorter, but I tried to keep the logic fairly easy to read. Enjoy!
UPDATE / EDIT
I thought about it and realized that though my existing method does exactly what your original question requested, it did it in O(n^2) time, which is comparatively slow. But if we use hash keys for each column's letters (one letter per key), and do a count of how many times each letter appears in the column (as the value of the hash element), we could do our summations in O(1) time, and our traversal of the list in O(n*c) time (where c is the number of columns, and n is the number of words). There's some setup time too (creation of the hash). But we still have a big improvement. Here is a new version of each technique, as well as a benchmark comparison of each.
use strict;
use warnings;
use List::Util qw/ max sum /;
use Benchmark qw/ cmpthese /;
my #words = qw/
PARTNERSHIPS
REPRIMANDING
CIVILIZATION
APPRECIATION
CONVERSATION
CIRCUMSTANCE
PURIFICATION
SECLUSIONIST
CONSTRUCTION
DISAPPEARING
TRANSMISSION
APPREHENSIVE
ENCOUNTERING
/;
# Just a test run for each solution.
my( $top, $indexes_ref );
($top, $indexes_ref ) = find_top_matches_force( \#words );
print "Testing force method: $top matches.\n";
print "#words[#$indexes_ref]\n";
( $top, $indexes_ref ) = find_top_matches_hash( \#words );
print "Testing hash method: $top matches.\n";
print "#words[#$indexes_ref]\n";
my $count = 20000;
cmpthese( $count, {
'Hash' => sub{ find_top_matches_hash( \#words ); },
'Force' => sub{ find_top_matches_force( \#words ); },
} );
sub find_top_matches_hash {
my $words = shift;
my #scores;
my $columns;
my $max_col = max( map { length $_ } #{$words} ) - 1;
foreach my $col_idx ( 0 .. $max_col ) {
$columns->[$col_idx]{ substr $_, $col_idx, 1 }++
for #{$words};
}
foreach my $word ( #{$words} ) {
my $score = sum(
map{
$columns->[$_]{ substr $word, $_, 1 } - 1
} 0 .. $max_col
);
push #scores, $score;
}
my $max = max( #scores );
my ( #max_ixs ) = grep { $scores[$_] == $max } 0 .. $#scores;
return( $max, \#max_ixs );
}
sub find_top_matches_force {
my $words = shift;
my #scores;
foreach my $word ( #{$words} ) {
my $score;
foreach my $comp_word ( #{$words} ) {
next if $comp_word eq $word;
foreach my $pos ( 0 .. ( length $word ) - 1 ) {
$score++ if
substr( $word, $pos, 1 ) eq substr( $comp_word, $pos, 1);
}
}
push #scores, $score;
}
my $max = max( #scores );
my ( #max_ixs ) = grep { $scores[$_] == $max } 0 .. $#scores;
return( $max, \#max_ixs );
}
The output is:
Testing force method: 39 matches.
APPRECIATION
Testing hash method: 39 matches.
APPRECIATION
Rate Force Hash
Force 2358/s -- -74%
Hash 9132/s 287% --
I realize your original spec changed after you saw some of the other options provided, and that's sort of the nature of innovation to a degree, but the puzzle was still alive in my mind. As you can see, my hash method is 287% faster than the original method. More fun in less time!
As a starting point, you can efficiently check how many letters they have in common with:
$count = ($word1 ^ $word2) =~ y/\0//;
But that's only useful if you loop through all possible pairs of words, something that isn't necessary in this case:
use strict;
use warnings;
my #words = qw/
BAKER
SALER
BALER
CARER
RUFFR
/;
# you want a hash to indicate which letters are present how many times in each position:
my %count;
for my $word (#words) {
my #letters = split //, $word;
$count{$_}{ $letters[$_] }++ for 0..$#letters;
}
# then for any given word, you get the count for each of its letters minus one (because the word itself is included in the count), and see if it is a maximum (so far) for any position or for the total:
my %max_common_letters_count;
my %max_common_letters_words;
for my $word (#words) {
my #letters = split //, $word;
my $total;
for my $position (0..$#letters, 'total') {
my $count;
if ( $position eq 'total' ) {
$count = $total;
}
else {
$count = $count{$position}{ $letters[$position] } - 1;
$total += $count;
}
if ( ! $max_common_letters_count{$position} || $count >= $max_common_letters_count{$position} ) {
if ( $max_common_letters_count{$position} && $count == $max_common_letters_count{$position} ) {
push #{ $max_common_letters_words{$position} }, $word;
}
else {
$max_common_letters_count{$position} = $count;
$max_common_letters_words{$position} = [ $word ];
}
}
}
}
# then show the maximum words for each position and in total:
for my $position ( sort { $a <=> $b } grep $_ ne 'total', keys %max_common_letters_count ) {
printf( "Position %s had a maximum of common letters of %s in words: %s\n",
$position,
$max_common_letters_count{$position},
join(', ', #{ $max_common_letters_words{$position} })
);
}
printf( "The maximum total common letters was %s in words(s): %s\n",
$max_common_letters_count{'total'},
join(', ', #{ $max_common_letters_words{'total'} })
);
Here's a complete script. It uses the same idea that ysth mentioned (although I had it independently). Use bitwise xor to combine the strings, and then count the number of NULs in the result. As long as your strings are ASCII, that will tell you how many matching letters there were. (That comparison is case sensitive, and I'm not sure what would happen if the strings were UTF-8. Probably nothing good.)
use strict;
use warnings;
use 5.010;
use List::Util qw(max);
sub findMatches
{
my ($words) = #_;
# Compare each word to every other word:
my #matches = (0) x #$words;
for my $i (0 .. $#$words-1) {
for my $j ($i+1 .. $#$words) {
my $m = ($words->[$i] ^ $words->[$j]) =~ tr/\0//;
$matches[$i] += $m;
$matches[$j] += $m;
}
}
# Find how many matches in the best word:
my $max = max(#matches);
# Find the words with that many matches:
my #wanted = grep { $matches[$_] == $max } 0 .. $#matches;
wantarray ? #$words[#wanted] : $words->[$wanted[0]];
} # end findMatches
my #words = qw(
BAKER
SALER
BALER
CARER
RUFFR
);
say for findMatches(\#words);
Haven't touched perl in a while, so pseudo-code it is. This isn't the fastest algorithm, but it will work fine for a small amount of words.
totals = new map #e.g. an object to map :key => :value
for each word a
for each word b
next if a equals b
totals[a] = 0
for i from 1 to a.length
if a[i] == b[i]
totals[a] += 1
end
end
end
end
return totals.sort_by_key.last
Sorry about the lack of perl, but if you code this into perl, it should work like a charm.
A quick note on run-time: this will run in time number_of_words^2 * length_of_words, so on a list of 100 words, each of length 10 characters, this will run in 100,000 cycles, which is adequate for most applications.
Here's a version that relies on transposing the words in order to count the identical characters. I used the words from your original comparison, not the code.
This should work with any length words, and any length list. Output is:
Word score
---- -----
BALER 12
SALER 11
BAKER 11
CARER 10
RUFFR 4
The code:
use warnings;
use strict;
my #w = qw(BAKER SALER BALER CARER RUFFR);
my #tword = t_word(#w);
my #score;
push #score, str_count($_) for #tword;
#score = t_score(#score);
my %total;
for (0 .. $#w) {
$total{$w[$_]} = $score[$_];
}
print "Word\tscore\n";
print "----\t-----\n";
print "$_\t$total{$_}\n" for (sort { $total{$b} <=> $total{$a} } keys %total);
# transpose the words
sub t_word {
my #w = #_;
my #tword;
for my $word (#w) {
my $i = 0;
while ($word =~ s/(.)//) {
$tword[$i++] .= $1;
}
}
return #tword;
}
# turn each character into a count
sub str_count {
my $str = uc(shift);
while ( $str =~ /([A-Z])/ ) {
my $chr = $1;
my $num = () = $str =~ /$chr/g;
$num--;
$str =~ s/$chr/$num /g;
}
return $str;
}
# sum up the character counts
# while reversing the transpose
sub t_score {
my #count = #_;
my #score;
for my $num (#count) {
my $i = 0;
while( $num =~ s/(\d+) //) {
$score[$i++] += $1;
}
}
return #score;
}
Here is my attempt at an answer. This will also allow you to see each individual match if you need it. (ie. BALER matches 4 characters in BAKER). EDIT: It now catches all matches if there is a tie between words (I added "CAKER" to the list to test).
#! usr/bin/perl
use strict;
use warnings;
my #wordlist = qw( BAKER SALER BALER CARER RUFFR CAKER);
my %wordcomparison;
#foreach word, break it into letters, then compare it against all other words
#break all other words into letters and loop through the letters (both words have same amount), adding to the count of matched characters each time there's a match
foreach my $word (#wordlist) {
my #letters = split(//, $word);
foreach my $otherword (#wordlist) {
my $count;
next if $otherword eq $word;
my #otherwordletters = split (//, $otherword);
foreach my $i (0..$#letters) {
$count++ if ( $letters[$i] eq $otherwordletters[$i] );
}
$wordcomparison{"$word"}{"$otherword"} = $count;
}
}
# sort (unnecessary) and loop through the keys of the hash (words in your list)
# foreach key, loop through the other words it compares with
#Add a new key: total, and sum up all the matched characters.
foreach my $word (sort keys %wordcomparison) {
foreach ( sort keys %{ $wordcomparison{$word} }) {
$wordcomparison{$word}{total} += $wordcomparison{$word}{$_};
}
}
#Want $word with highest total
my #max_match = (sort { $wordcomparison{$b}{total} <=> $wordcomparison{$a}{total} } keys %wordcomparison );
#This is to get all if there is a tie:
my $maximum = $max_match[0];
foreach (#max_match) {
print "$_\n" if ($wordcomparison{$_}{total} >= $wordcomparison{$maximum}{total} )
}
The output is simply: CAKER BALER and BAKER.
The hash %wordcomparison looks like:
'SALER'
{
'RUFFR' => 1,
'BALER' => 4,
'BAKER' => 3,
'total' => 11,
'CARER' => 3
};
You can do this, using a dirty regex trick to execute code if a letter matches in its place, but not otherwise, thankfully it's quite easy to build the regexes as you go:
An example regular expression is:
(?:(C(?{ $c++ }))|.)(?:(A(?{ $c++ }))|.)(?:(R(?{ $c++ }))|.)(?:(E(?{ $c++ }))|.)(?:(R(?{ $c++ }))|.)
This may or may not be fast.
use 5.12.0;
use warnings;
use re 'eval';
my #words = qw(BAKER SALER BALER CARER RUFFR);
my ($best, $count) = ('', 0);
foreach my $word (#words) {
our $c = 0;
foreach my $candidate (#words) {
next if $word eq $candidate;
my $regex_str = join('', map {"(?:($_(?{ \$c++ }))|.)"} split '', $word);
my $regex = qr/^$regex_str$/;
$candidate =~ $regex or die "did not match!";
}
say "$word $c";
if ($c > $count) {
$best = $word;
$count = $c;
}
}
say "Matching: first best: $best";
Using xor trick will be fast but assumes a lot about the range of characters you might encounter. There are many ways in which utf-8 will break with that case.
Many thanks to all the contributers! You've certainly shown me that I still have a lot to learn, but you have also helped me tremendously in working out my own answer. I'm just putting it here for reference and possible feedback, since there are probably better ways of doing it. To me this was the simplest and most straight forward approach I could find on my own. Enjøy! :)
#!/usr/bin/perl
use strict;
use warnings;
# a list of words for testing
my #list = qw(
BAKER
SALER
BALER
CARER
RUFFR
);
# populate two dimensional array with the list,
# so we can compare each letter with the other letters on the same row more easily
my $list_length = #list;
my #words;
for (my $i = 0; $i < $list_length; $i++) {
my #letters = split(//, $list[$i]);
my $letters_length = #letters;
for (my $j = 0; $j < $letters_length; $j++) {
$words[$i][$j] = $letters[$j];
}
}
# this gives a two-dimensionla array:
#
# #words = ( ["B", "A", "K", "E", "R"],
# ["S", "A", "L", "E", "R"],
# ["B", "A", "L", "E", "R"],
# ["C", "A", "R", "E", "R"],
# ["R", "U", "F", "F", "R"],
# );
# now, on to find the word with most letters in common with the other on the same row
# add up the score for each letter in each word
my $word_length = #words;
my #letter_score;
for my $i (0 .. $#words) {
for my $j (0 .. $#{$words[$i]}) {
for (my $k = 0; $k < $word_length; $k++) {
if ($words[$i][$j] eq $words[$k][$j]) {
$letter_score[$i][$j] += 1;
}
}
# we only want to add in matches outside the one we're testing, therefore
$letter_score[$i][$j] -= 1;
}
}
# sum each score up
my #scores;
for my $i (0 .. $#letter_score ) {
for my $j (0 .. $#{$letter_score[$i]}) {
$scores[$i] += $letter_score[$i][$j];
}
}
# find the highest score
my $max = $scores[0];
foreach my $i (#scores[1 .. $#scores]) {
if ($i > $max) {
$max = $i;
}
}
# and print it all out :D
for my $i (0 .. $#letter_score ) {
print "$list[$i]: $scores[$i]";
if ($scores[$i] == $max) {
print " <- best";
}
print "\n";
}
When run, the script yields the following:
BAKER: 11
SALER: 11
BALER: 12 <- best
CARER: 10
RUFFR: 4

Difference of Two Arrays Using Perl

I have two arrays. I need to check and see if the elements of one appear in the other one.
Is there a more efficient way to do it than nested loops? I have a few thousand elements in each and need to run the program frequently.
Another way to do it is to use Array::Utils
use Array::Utils qw(:all);
my #a = qw( a b c d );
my #b = qw( c d e f );
# symmetric difference
my #diff = array_diff(#a, #b);
# intersection
my #isect = intersect(#a, #b);
# unique union
my #unique = unique(#a, #b);
# check if arrays contain same members
if ( !array_diff(#a, #b) ) {
# do something
}
# get items from array #a that are not in array #b
my #minus = array_minus( #a, #b );
perlfaq4 to the rescue:
How do I compute the difference of two arrays? How do I compute the intersection of two arrays?
Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:
#union = #intersection = #difference = ();
%count = ();
foreach $element (#array1, #array2) { $count{$element}++ }
foreach $element (keys %count) {
push #union, $element;
push #{ $count{$element} > 1 ? \#intersection : \#difference }, $element;
}
If you properly declare your variables, the code looks more like the following:
my %count;
for my $element (#array1, #array2) { $count{$element}++ }
my ( #union, #intersection, #difference );
for my $element (keys %count) {
push #union, $element;
push #{ $count{$element} > 1 ? \#intersection : \#difference }, $element;
}
You need to provide a lot more context. There are more efficient ways of doing that ranging from:
Go outside of Perl and use shell (sort + comm)
map one array into a Perl hash and then loop over the other one checking hash membership. This has linear complexity ("M+N" - basically loop over each array once) as opposed to nested loop which has "M*N" complexity)
Example:
my %second = map {$_=>1} #second;
my #only_in_first = grep { !$second{$_} } #first;
# use a foreach loop with `last` instead of "grep"
# if you only want yes/no answer instead of full list
Use a Perl module that does the last bullet point for you (List::Compare was mentioned in comments)
Do it based on timestamps of when elements were added if the volume is very large and you need to re-compare often. A few thousand elements is not really big enough, but I recently had to diff 100k sized lists.
You can try Arrays::Utils, and it makes it look nice and simple, but it's not doing any powerful magic on the back end. Here's the array_diffs code:
sub array_diff(\#\#) {
my %e = map { $_ => undef } #{$_[1]};
return #{[ ( grep { (exists $e{$_}) ? ( delete $e{$_} ) : ( 1 ) } #{ $_[0] } ), keys %e ] };
}
Since Arrays::Utils isn't a standard module, you need to ask yourself if it's worth the effort to install and maintain this module. Otherwise, it's pretty close to DVK's answer.
There are certain things you must watch out for, and you have to define what you want to do in that particular case. Let's say:
#array1 = qw(1 1 2 2 3 3 4 4 5 5);
#array2 = qw(1 2 3 4 5);
Are these arrays the same? Or, are they different? They have the same values, but there are duplicates in #array1 and not #array2.
What about this?
#array1 = qw( 1 1 2 3 4 5 );
#array2 = qw( 1 1 2 3 4 5 );
I would say that these arrays are the same, but Array::Utils::arrays_diff begs to differ. This is because Array::Utils assumes that there are no duplicate entries.
And, even the Perl FAQ pointed out by mob also says that It assumes that each element is unique in a given array. Is this an assumption you can make?
No matter what, hashes are the answer. It's easy and quick to look up a hash. The problem is what do you want to do with unique values.
Here's a solid solution that assumes duplicates don't matter:
sub array_diff {
my #array1 = #{ shift() };
my #array2 = #{ shift() };
my %array1_hash;
my %array2_hash;
# Create a hash entry for each element in #array1
for my $element ( #array1 ) {
$array1_hash{$element} = #array1;
}
# Same for #array2: This time, use map instead of a loop
map { $array_2{$_} = 1 } #array2;
for my $entry ( #array2 ) {
if ( not $array1_hash{$entry} ) {
return 1; #Entry in #array2 but not #array1: Differ
}
}
if ( keys %array_hash1 != keys %array_hash2 ) {
return 1; #Arrays differ
}
else {
return 0; #Arrays contain the same elements
}
}
If duplicates do matter, you'll need a way to count them. Here's using map not just to create a hash keyed by each element in the array, but also count the duplicates in the array:
my %array1_hash;
my %array2_hash;
map { $array1_hash{$_} += 1 } #array1;
map { $array2_hash{$_} += 2 } #array2;
Now, you can go through each hash and verify that not only do the keys exist, but that their entries match
for my $key ( keys %array1_hash ) {
if ( not exists $array2_hash{$key}
or $array1_hash{$key} != $array2_hash{$key} ) {
return 1; #Arrays differ
}
}
You will only exit the for loop if all of the entries in %array1_hash match their corresponding entries in %array2_hash. Now, you have to show that all of the entries in %array2_hash also match their entries in %array1_hash, and that %array2_hash doesn't have more entries. Fortunately, we can do what we did before:
if ( keys %array2_hash != keys %array1_hash ) {
return 1; #Arrays have a different number of keys: Don't match
}
else {
return; #Arrays have the same keys: They do match
}
You can use this for getting diffrence between two arrays
#!/usr/bin/perl -w
use strict;
my #list1 = (1, 2, 3, 4, 5);
my #list2 = (2, 3, 4);
my %diff;
#diff{ #list1 } = undef;
delete #diff{ #list2 };
You want to compare each element of #x against the element of the same index in #y, right? This will do it.
print "Index: $_ => \#x: $x[$_], \#y: $y[$_]\n"
for grep { $x[$_] != $y[$_] } 0 .. $#x;
...or...
foreach( 0 .. $#x ) {
print "Index: $_ => \#x: $x[$_], \#y: $y[$_]\n" if $x[$_] != $y[$_];
}
Which you choose kind of depends on whether you're more interested in keeping a list of indices to the dissimilar elements, or simply interested in processing the mismatches one by one. The grep version is handy for getting the list of mismatches. (original post)
n + n log n algorithm, if sure that elements are unique in each array (as hash keys)
my %count = ();
foreach my $element (#array1, #array2) {
$count{$element}++;
}
my #difference = grep { $count{$_} == 1 } keys %count;
my #intersect = grep { $count{$_} == 2 } keys %count;
my #union = keys %count;
So if I'm not sure of unity and want to check presence of the elements of array1 inside array2,
my %count = ();
foreach (#array1) {
$count{$_} = 1 ;
};
foreach (#array2) {
$count{$_} = 2 if $count{$_};
};
# N log N
if (grep { $_ == 1 } values %count) {
return 'Some element of array1 does not appears in array2'
} else {
return 'All elements of array1 are in array2'.
}
# N + N log N
my #a = (1,2,3);
my #b=(2,3,1);
print "Equal" if grep { $_ ~~ #b } #a == #b;
Not elegant, but easy to understand:
#!/usr/local/bin/perl
use strict;
my $file1 = shift or die("need file1");
my $file2 = shift or die("need file2");;
my #file1lines = split/\n/,`cat $file1`;
my #file2lines = split/\n/,`cat $file2`;
my %lines;
foreach my $file1line(#file1lines){
$lines{$file1line}+=1;
}
foreach my $file2line(#file2lines){
$lines{$file2line}+=2;
}
while(my($key,$value)=each%lines){
if($value == 1){
print "$key is in only $file1\n";
}elsif($value == 2){
print "$key is in only $file2\n";
}elsif($value == 3){
print "$key is in both $file1 and $file2\n";
}
}
exit;
__END__
Try to use List::Compare. IT has solutions for all the operations that can be performed on arrays.

find extra, missing, invalid strings when comparing two lists in perl

List-1 List-2
one one
two three
three three
four four
five six
six seven
eight eighttt
nine nine
Looking to output
one | one PASS
two | * FAIL MISSING
three | three PASS
* | three FAIL EXTRA
four | four PASS
five | * FAIL MISSING
six | six PASS
* | seven FAIL EXTRA
eight | eighttt FAIL INVALID
nine | nine PASS
Actually the return from my current solution is a reference to the two modified lists and a reference to a "fail" list describing the failure for the index as either "no fail", "missing", "extra", or "invalid" which is also (obviously) fine output.
My current solution is:
sub compare {
local $thisfound = shift;
local $thatfound = shift;
local #thisorig = #{ $thisfound };
local #thatorig = #{ $thatfound };
local $best = 9999;
foreach $n (1..6) {
local $diff = 0;
local #thisfound = #thisorig;
local #thatfound = #thatorig;
local #fail = ();
for (local $i=0;$i<scalar(#thisfound) || $i<scalar(#thatfound);$i++) {
if($thisfound[$i] eq $thatfound[$i]) {
$fail[$i] = 'NO_FAIL';
next;
}
if($n == 1) { # 1 2 3
next unless __compare_missing__();
next unless __compare_extra__();
next unless __compare_invalid__();
} elsif($n == 2) { # 1 3 2
next unless __compare_missing__();
next unless __compare_invalid__();
next unless __compare_extra__();
} elsif($n == 3) { # 2 1 3
next unless __compare_extra__();
next unless __compare_missing__();
next unless __compare_invalid__();
} elsif($n == 4) { # 2 3 1
next unless __compare_extra__();
next unless __compare_invalid__();
next unless __compare_missing__();
} elsif($n == 5) { # 3 1 2
next unless __compare_invalid__();
next unless __compare_missing__();
next unless __compare_extra__();
} elsif($n == 6) { # 3 2 1
next unless __compare_invalid__();
next unless __compare_extra__();
next unless __compare_missing__();
}
push #fail,'INVALID';
$diff += 1;
}
if ($diff<$best) {
$best = $diff;
#thisbest = #thisfound;
#thatbest = #thatfound;
#failbest = #fail;
}
}
return (\#thisbest,\#thatbest,\#failbest)
}
sub __compare_missing__ {
my $j;
### Does that command match a later this command? ###
### If so most likely a MISSING command ###
for($j=$i+1;$j<scalar(#thisfound);$j++) {
if($thisfound[$j] eq $thatfound[$i]) {
$diff += $j-$i;
for ($i..$j-1) { push(#fail,'MISSING'); }
#end = #thatfound[$i..$#thatfound];
#thatfound = #thatfound[0..$i-1];
for ($i..$j-1) { push(#thatfound,'*'); }
push(#thatfound,#end);
$i=$j-1;
last;
}
}
$j == scalar(#thisfound);
}
sub __compare_extra__ {
my $j;
### Does this command match a later that command? ###
### If so, most likely an EXTRA command ###
for($j=$i+1;$j<scalar(#thatfound);$j++) {
if($thatfound[$j] eq $thisfound[$i]) {
$diff += $j-$i;
for ($i..$j-1) { push(#fail,'EXTRA'); }
#end = #thisfound[$i..$#thisfound];
#thisfound = #thisfound[0..$i-1];
for ($i..$j-1) { push (#thisfound,'*'); }
push(#thisfound,#end);
$i=$j-1;
last;
}
}
$j == scalar(#thatfound);
}
sub __compare_invalid__ {
my $j;
### Do later commands match? ###
### If so most likely an INVALID command ###
for($j=$i+1;$j<scalar(#thisfound);$j++) {
if($thisfound[$j] eq $thatfound[$j]) {
$diff += $j-$i;
for ($i..$j-1) { push(#fail,'INVALID'); }
$i=$j-1;
last;
}
}
$j == scalar(#thisfound);
}
But this isn't perfect ... who wants to simplify and improve? Specifically ... within a single data set, one order of searching is better for a subset and another order is better for a different subset.
If the arrays contain duplicate values, the answer is quite a bit more complicated than that.
See e.g. Algorithm::Diff or read about Levenshtein distance.
From perlfaq4's answer to How can I tell whether a certain element is contained in a list or array?:
(portions of this answer contributed by Anno Siegel and brian d foy)
Hearing the word "in" is an indication that you probably should have used a hash, not a list or array, to store your data. Hashes are designed to answer this question quickly and efficiently. Arrays aren't.
That being said, there are several ways to approach this. In Perl 5.10 and later, you can use the smart match operator to check that an item is contained in an array or a hash:
use 5.010;
if( $item ~~ #array )
{
say "The array contains $item"
}
if( $item ~~ %hash )
{
say "The hash contains $item"
}
With earlier versions of Perl, you have to do a bit more work. If you are going to make this query many times over arbitrary string values, the fastest way is probably to invert the original array and maintain a hash whose keys are the first array's values:
#blues = qw/azure cerulean teal turquoise lapis-lazuli/;
%is_blue = ();
for (#blues) { $is_blue{$_} = 1 }
Now you can check whether $is_blue{$some_color}. It might have been a good idea to keep the blues all in a hash in the first place.
If the values are all small integers, you could use a simple indexed array. This kind of an array will take up less space:
#primes = (2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31);
#is_tiny_prime = ();
for (#primes) { $is_tiny_prime[$_] = 1 }
# or simply #istiny_prime[#primes] = (1) x #primes;
Now you check whether $is_tiny_prime[$some_number].
If the values in question are integers instead of strings, you can save quite a lot of space by using bit strings instead:
#articles = ( 1..10, 150..2000, 2017 );
undef $read;
for (#articles) { vec($read,$_,1) = 1 }
Now check whether vec($read,$n,1) is true for some $n.
These methods guarantee fast individual tests but require a re-organization of the original list or array. They only pay off if you have to test multiple values against the same array.
If you are testing only once, the standard module List::Util exports the function first for this purpose. It works by stopping once it finds the element. It's written in C for speed, and its Perl equivalent looks like this subroutine:
sub first (&#) {
my $code = shift;
foreach (#_) {
return $_ if &{$code}();
}
undef;
}
If speed is of little concern, the common idiom uses grep in scalar context (which returns the number of items that passed its condition) to traverse the entire list. This does have the benefit of telling you how many matches it found, though.
my $is_there = grep $_ eq $whatever, #array;
If you want to actually extract the matching elements, simply use grep in list context.
my #matches = grep $_ eq $whatever, #array;
sub compare {
local #d = ();
my $this = shift;
my $that = shift;
my $distance = _levenshteindistance($this, $that);
my #thisorig = #{ $this };
my #thatorig = #{ $that };
my $s = $#thisorig;
my $t = $#thatorig;
#this = ();
#that = ();
#fail = ();
while($s>0 || $t>0) {
# deletion, insertion, substitution
my $min = _minimum($d[$s-1][$t],$d[$s][$t-1],$d[$s-1][$t-1]);
if($min == $d[$s-1][$t-1]) {
unshift(#this,$thisorig[$s]);
unshift(#that,$thatorig[$t]);
if($d[$s][$t] > $d[$s-1][$t-1]) {
unshift(#fail,'INVALID');
} else {
unshift(#fail,'NO_FAIL');
}
$s -= 1;
$t -= 1;
} elsif($min == $d[$s][$t-1]) {
unshift(#this,'*');
unshift(#that,$thatorig[$t]);
unshift(#fail,'EXTRA');
$t -= 1;
} elsif($min == $d[$s-1][$t]) {
unshift(#this,$thisorig[$s]);
unshift(#that,'*');
unshift(#fail,'MISSING');
$s -= 1;
} else {
die("Error! $!");
}
}
return(\#this, \#that, \#fail);
}
sub _minimum {
my $ret = 2**53;
foreach $in (#_) {
$ret = $ret < $in ? $ret : $in;
}
$ret;
}
sub _levenshteindistance {
my $s = shift;
my $t = shift;
my #s = #{ $s };
my #t = #{ $t };
for(my $i=0;$i<scalar(#s);$i++) {
$d[$i] = ();
}
for(my $i=0;$i<scalar(#s);$i++) {
$d[$i][0] = $i # deletion
}
for(my $j=0;$j<scalar(#t);$j++) {
$d[0][$j] = $j # insertion
}
for(my $j=1;$j<scalar(#t);$j++) {
for(my $i=1;$i<scalar(#s);$i++) {
if ($s[$i] eq $t[$j]) {
$d[$i][$j] = $d[$i-1][$j-1];
} else {
# deletion, insertion, substitution
$d[$i][$j] = _minimum($d[$i-1][$j]+1,$d[$i][$j-1]+1,$d[$i-1][$j-1]+1);
}
}
}
foreach $a (#d) {
#a = #{ $a };
foreach $b (#a) {
printf STDERR "%2d ",$b;
}
print STDERR "\n";
}
return $d[$#s][$#t];
}
The trick in Perl (and similar languages) is the hash, which doesn't care about order.
Suppose that the first array is the one that hold the valid elements. Construct a hash with those values as keys:
my #valid = qw( one two ... );
my %valid = map { $_, 1 } #valid;
Now, to find the invalid elements, you just have to find the ones not in the %valid hash:
my #invalid = grep { ! exists $valid{$_} } #array;
If you want to know the array indices of the invalid elements:
my #invalid_indices = grep { ! exists $valid{$_} } 0 .. $#array;
Now, you can expand that to find the repeated elements too. Not only do you check the %valid hash, but also keep track of what you have already seen:
my %Seen;
my #invalid_indices = grep { ! exists $valid{$_} && ! $Seen{$_}++ } 0 .. $#array;
The repeated valid elements are the ones with a value in %Seen that is greater than 1:
my #repeated_valid = grep { $Seen{$_} > 1 } #valid;
To find the missing elements, you look in %Seen to check what isn't in there.
my #missing = grep { ! $Seen{$_ } } #valid;
From perlfaq4's answer to How do I compute the difference of two arrays? How do I compute the intersection of two arrays?:
Use a hash. Here's code to do both and more. It assumes that each element is unique in a given array:
#union = #intersection = #difference = ();
%count = ();
foreach $element (#array1, #array2) { $count{$element}++ }
foreach $element (keys %count) {
push #union, $element;
push #{ $count{$element} > 1 ? \#intersection : \#difference }, $element;
}
Note that this is the symmetric difference, that is, all elements in either A or in B but not in both. Think of it as an xor operation.

How do I store a duplicate value from an array or hash in Perl?

Let's make this very easy. What I want:
#array = qw/one two one/;
my #duplicates = duplicate(#array);
print "#duplicates"; # This should now print 'one'.
How to print duplicate values of a array/hash?
sub duplicate {
my #args = #_;
my %items;
for my $element(#args) {
$items{$element}++;
}
return grep {$items{$_} > 1} keys %items;
}
# assumes inputs can be hash keys
#a = (1, 2, 3, 3, 4, 4, 5);
# keep count for each unique input
%h = ();
map { $h{$_}++ } #a;
# duplicate inputs have count > 1
#dupes = grep { $h{$_} > 1 } keys %h;
# should print 3, 4
print join(", ", sort #dupes), "\n";
The extra verbose, extra readable version of what you want to do:
sub duplicate {
my %value_hash;
foreach my $val (#_) {
$value_hash{$val} +=1;
}
my #arr;
while (my ($val, $num) = each(%value_hash)) {
if ($num > 1) {
push(#arr, $val)
}
}
return #arr;
}
This can be shortened considerably, but I intentionally left it verbose so that you can follow along.
I didn't test it, though, so watch out for my typos.
Use a dictionary, put the value in the key, and the count in the value.
Ah, just noticed you've tagged as perl
while ([...]) {
$hash{[dbvalue]}++
}
Unspecified in the question is the order in which the duplicates should be returned.
I can think of several possibilities: don't care; by order of first/second/last occurrence in the input list; sorted.
I'm going golfing!
sub duplicate {
my %count;
grep $count{$_}++, #_;
}
#array = qw/one two one/;
my #duplicates = duplicate(#array);
print "#duplicates"; # This should now print 'one'.
# or if returning *exactly* 1 occurrence of each duplicated item is important
sub duplicate {
my %count;
grep ++$count{$_} == 2, #_;
}