Perl need the right grep operator to match value of variable - perl

Question

I want to see if I have repeated items in my array, there are over 16.000 so will automate it
There may be other ways but I started with this and, well, would like to finish it unless there is a straightforward command. What I am doing is shifting and pushing from one array into another and this way, check the destination array to see if it is "in array" (like there is such a command in PHP).
So, I got this sub routine and it works with literals, but it doesn't with variables. It is because of the 'eq' or whatever I should need. The 'sourcefile' will contain one or more of the words of the destination array.
// Here I just fetch my file
$listamails = <STDIN>;
# Remove the newlines filename
chomp $listamails;
# open the file, or exit
unless ( open(MAILS, $listamails) ) {
print "Cannot open file \"$listamails\"\n\n";
exit;
}
# Read the list of mails from the file, and store it
# into the array variable #sourcefile
#sourcefile = <MAILS>;
# Close the handle - we've read all the data into #sourcefile now.
close MAILS;
my #destination = ('hi', 'bye');
sub in_array
{
my ($destination,$search_for) = #_;
return grep {$search_for eq $_} #$destination;
}
for($i = 0; $i <=100; $i ++)
{
$elemento = shift #sourcefile;
if(in_array(\#destination, $elemento))
{
print "it is";
}
else
{
print "it aint there";
}
}
Well, if instead of including the $elemento in there I put a 'hi' it does work and also I have printed the value of $elemento which is also 'hi', but when I put the variable, it does not work, and that is because of the 'eq', but I don't know what else to put. If I put == it complains that 'hi' is not a numeric value.

Answer 1

When you want distinct values think hash.
my %seen;
#seen{ #array } = ();
if (keys %seen == #array) {
print "\#array has no duplicate values\n";
}

Answer 2

It's not clear what you want. If your first sentence is the only one that matters ("I want to see if I have repeated items in my array"), then you could use:
my %seen;
if (grep ++$seen{$_} >= 2, #array) {
say "Has duplicates";
}
You said you have a large array, so it might be faster to stop as soon as you find a duplicate.
my %seen;
for (#array) {
if (++$seen{$_} == 2) {
say "Has duplicates";
last;
}
}

Answer 3

By the way, when looking for duplicates in a large number of items, it's much faster to use a strategy based on sorting. After sorting the items, all duplicates will be right next to each other, so to tell if something is a duplicate, all you have to do is compare it with the previous one:
#sorted = sort #sourcefile;
for (my $i = 1; $i < #sorted; ++$i) { # Start at 1 because we'll check the previous one
print "$sorted[$i] is a duplicate!\n" if $sorted[$i] eq $sorted[$i - 1];
}
This will print multiple dupe messages if there are multiple dupes, but you can clean it up.

Answer 4

As eugene y said, hashes are definitely the way to go here. Here's a direct translation of the code you posted to a hash-based method (with a little more Perlishness added along the way):
my #destination = ('hi', 'bye');
my %in_array = map { $_ => 1 } #destination;
for my $i (0 .. 100) {
$elemento = shift #sourcefile;
if(exists $in_array{$elemento})
{
print "it is";
}
else
{
print "it aint there";
}
}
Also, if you mean to check all elements of #sourcefile (as opposed to testing the first 101 elements) against #destination, you should replace the for line with
while (#sourcefile) {
Also also, don't forget to chomp any values read from a file! Lines read from a file have a linebreak at the end of them (the \r\n or \n mentioned in comments on the initial question), which will cause both eq and hash lookups to report that otherwise-matching values are different. This is, most likely, the reason why your code is failing to work correctly in the first place and changing to use sort or hashes won't fix that. First chomp your input to make it work, then use sort or hashes to make it efficient.