in reply to finding the first unique element in an array

Instead of remembering the elements in @uniq, directly print them out:

my @uniq;
my %seen = ();

for my $i (0..$#name1)  {
        if (!$seen{$name1[$i]}) {
          push (@uniq, $name1[$i]);
          print "$name1[$i]\t$name2[$i]\t$percent[$i]\n";
        };
}

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As an aside, I've removed your C-style loop, which is error-prone, and changed it into a more perlish loop.

Your data structures also scream for a hash, as using parallel arrays also is error prone; it's not always convenient to rearrange your data into concentrated data structures, especially if the arrays get filled from separate data streams.

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Re^2: finding the first unique element in an array
by Anonymous Monk on Jul 19, 2005 at 10:02 UTC
    As an aside, I've removed your C-style loop, which is error-prone
    Error-prone is in the eye of the beholder, and the C-style loop avoids the ugly $#array syntax.
    Your data structures also scream for a hash, as using parallel arrays also is error prone
    That would be a array of hashes then. But that has a severe drawback: it uses a lot of memory. Aggregates have a lot of overhead in Perl. The three parallel arrays only use three aggregates - regardless of the number of entities stored. Putting each entity in its own hash gives you an aggregate for each entity (that is, for each element of the original @name1). And that adds up. Fast.

    Below is a program that shows the difference in memory usage . The hashes solution uses almost two and a half times the amount of memory. 

    #!/usr/bin/perl

use strict;
use warnings;
use Devel::Size qw 'total_size';

my $size = 100_000;
    
my (@name1, @name2, @percent);
my @big;

sub r_name {  # Make a random name.
    my $r = "";
    $r .= ('a' .. 'z')[rand 26] for 1 .. 3 + rand(5);
    return $r;
}

for (1 .. $size) {
    my $name1 = r_name;
    my $name2 = r_name;
    my $perc  = rand(100);

    push @name1, $name1;
    push @name2, $name2;
    push @percent, $perc;

    push @big, {name1 => $name1, name2 => $name2, percent => $perc};
}   

my $size_3 = total_size(\@name1) + total_size(\@name2) + total_size(\@
+percent);
my $size_1 = total_size(\@big);

printf "Three arrays:  %10d (%6.2f)\n",  $size_3, $size_3 / $size;
printf "One structure: %10d (%6.2f)\n",  $size_1, $size_1 / $size;
    
__END__
Three arrays:     9573279 ( 95.73)
One structure:   23724662 (237.25)

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Re^2: finding the first unique element in an array
by Limbic~Region (Chancellor) on Jul 19, 2005 at 14:45 UTC
    Corion,
    There is at least 1 problem with this code (and possibly 2). 
    if (!$seen{$name1[$i]}) {

should be

if ( ! $seen{$name1[$i]}++ ) {

    [download]
    Without the post-increment, everything would be pushed to the unique array. The second possible problem is one of interpretation. I read the original post to mean that there would be some unique entries in a list containing duplicates and the object was to find the first one. If that interpretation is correct - then you have to wait until after going through the first array in its entirety before you can know if an item is unique or not.

    Cheers - L~R

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