CODEWITHSUNDEEP
perl
Philippe A.
Philippe A.

Reputation: 2955

What is the most efficient method to iterate over a Perl array?

I am reading an ordered file for which I must count by-hour, by-minute or by-second occurrences. If requested, I must print times with 0 occurrences (normalized output) or skip them (non-normalized output). The output must obviously be ordered.

I first thought using an array. When the output is non normalized, I am doing roughly the equivalent of:

@array[10] = 100;
@array[10000] = 10000;

And to print the result:

foreach (@array) {
  print if defined;
}

Is there a way to reduce iterations to only elements defined in the array? In the previous example, that would mean doing only two iterations, instead of 10000 as using $#array implies. Then I would also need a way to know the current array index in a loop. Does such a thing exist?

I am thinking more and more to use a hash instead. Using a hash solves my problem and also eliminates the need to convert hh:mm:ss times to index and vice-versa.

Or do you have a better solution to suggest for this simple problem?

Upvotes: 1

Views: 254

Answers (2)

choroba
choroba

Reputation: 241808

You can also remember just the pairs of numbers in an array:

#!/usr/bin/perl
use warnings;
use strict;

my @ar = ( [  10, 100 ],
           [ 100,  99 ],
           [  12,   1 ],
           [  13,   2 ],
           [  15,   1 ],
         );

sub normalized {
    my @ar = sort { $a->[0] <=> $b->[0] } @_;
    map "@$_", @ar;
}

sub non_normalized {
    my @ar = sort { $a->[0] <=> $b->[0] } @_;
    unshift @ar, [0, 0] unless $ar[0][0] == 0;
    my @return;
    for my $i (0 .. $#ar) {
        push @return, "@{ $ar[$i] }";
        push @return, $_ . $" . 0 for 1 + $ar[$i][0] .. $ar[$i + 1][0] - 1;
    }
    return @return;
}


print join "\n", normalized(@ar), q();
print "\n";
print join "\n", non_normalized(@ar), q();

Upvotes: 2

Phil H
Phil H

Reputation: 20131

Yes, use a hash. You can iterate over the ordered array of the keys of the hash if your keys sort correctly.

Upvotes: 6

Related Questions