Compare 2 sets of numbers contained in strings - perl

Question

I have 2 scalars as below:
$a = '100 105 010';
$b = '010 105 100';
How do I compare if both has same set of values? order doesn't matter.
one way is to arrange it in ascending order and compare, is there a better way?

Answer 1

You can split each string into an array and sort and compare arrays. By hand:
use warnings;
use strict;
my $x = '100 105 1 010';
my $y = '010 105 100 2';
my #xs = sort { $a <=> $b } split ' ', $x;
my #ys = sort { $a <=> $b } split ' ', $y;
if (#xs != #ys) {
print "Differ in number of elements.\n";
}
else {
for (0..$#xs) {
print "Differ: $xs[$_] vs $ys[$_]\n" if $xs[$_] != $ys[$_];
}
}
# For boolean comparison put it in a sub
print arr_num_eq(\#xs, \#ys), "\n";
sub arr_num_eq {
my ($ra, $rb) = #_;
return 0 if #$ra != #$rb;
$ra->[$_] != $rb->[$_] && return 0 for 0..$#$ra;
return 1;
}
The sorting can be moved to the sub as well, which would then take strings. The way it stands it can be used for comparison of existing arrays as well. Please add argument checking.
There is a number of modules that have this capability. The perm from Array::Compare hides the sorting above, but internally joins sorted arrays into strings thus duplicating the work here since we started with strings. The List::AllUtils certainly offers this as well with its long list of utilities.
See this post, for example, for a few methods (just not the smart match ~~), and for benchmarks if efficiency is a concern.
Using the mentioned implementation idea from Array::Compare, per comment by ysth
sub str_num_eq {
return join(' ', sort { $a <=> $b } split / /, $_[0])
eq join(' ', sort { $a <=> $b } split / /, $_[1])
}
What the most suitable method is depends on what this is for and how it is used. Is it only a boolean comparison, or will more be done if they are found to differ? How does it come about in your program flow? What are typical sizes of strings, how often is it run? Are the strings most often the same or different, do they typically differ a lot or a little? Etc.

Answer 2

Without modules, you can use hashes:
#!/usr/bin/perl
use warnings;
use strict;
my $x = '100 105 010 2';
my $y = '010 105 100 100 1';
my (%hx, %hy);
$hx{$_}++ for split ' ', $x;
$hy{$_}++ for split ' ', $y;
for my $k (keys %hx) {
if (! exists $hy{$k}) {
print "$k missing in y\n";
} elsif ($hy{$k} != $hx{$k}) {
print "$k has different number of occurences\n";
}
delete $hy{$k};
}
print "$_ missing in x\n" for keys %hy;
$a and $b are special variables used in sort, so I renamed them to $x and $y.
split turns the strings into lists. Each hash counts how many times a member occurs in the list.
See also Perl FAQ 4.

Answer 3

Something else try with pattern matching,
This is not a straight forward but it will work.
Construct the pattern by anyone of your scalar value. Then check the another string by the constructed pattern.
my $a = '100 100 105';
my $b = '100 105 100';
my #b_ary = split(" ",$b);
my $regex = join'\b|\b', #b_ary;
my $word_length = #b_ary * 2 - 1; #Count the number of words and space.
my $rgx = qr"^(?:\b$regex\b|\s){$word_length}$"; #`{n}` match word exact n times
if($a=~m/$rgx/)
{
print "same values\n";
}
else
{
print "Not a same values\n";
}

Answer 4

The answer is already posted above. This is just in case you want to remove the white spaces and compare each number.
$x = '100 105 010';
$y = '010 105 100';
join("",sort split "",join("",split " ",$x)) eq join("",sort split "",join("",split " ",$y));