Beefy Boxes and Bandwidth Generously Provided by pair Networks
Perl: the Markov chain saw
 
PerlMonks  

Re: how to loop through many arrays

by Marshall (Canon)
on Jun 19, 2011 at 05:24 UTC ( [id://910378] : note . print w/replies, xml ) Need Help??


in reply to how to loop through many arrays

I think you are looking for the maximum of each column?
Perl operates easiest on rows. So one way to do this is to transpose the 2-D array, i.e. make the columns become rows. Here is how to do that...

Update: updated code to do what I think op is asking for..used wind's row code with List::Util::reduce() for a transposed "column".

#!/usr/bin/perl -w use strict; use List::Util qw(reduce max); my @array1=(1,2,3,4,8); my @array2=(1,4,2,4,5); my @array3=(1,6,1,7,5); my @AoA = (\@array1,\@array2,\@array3); my @transposed; print "Original array:\n"; printAoA(\@AoA); ## tranpose array to make it easy to do column operations ## i.e. columns become rows foreach my $rowref (@AoA) { my $i=0; foreach my $num (@$rowref) { push @{$transposed[$i++]}, $num; } } ## Now @transposed is an array of references to what used to be ## columns. print "\nMaximum of each column...\n". "coordinates based on row 0..n, col 0..n\n"; my $col=0; foreach my $colref (@transposed) { ## you could have a loop: foreach my $num (@$colref) {} here ## below is wind's use of reduce to get the column position of ## the first maximum, perhaps you have something different in ## mind? my $max_pos = reduce {$colref->[$b] > $colref->[$a] ? $b : $a} (0. +.@$colref-1); print "Max of column index $col is $colref->[$max_pos] at array in +dex $max_pos\n"; $col++; } print "\nTransposed array:\n"; printAoA(\@transposed); sub printAoA { my $refAoA = shift; foreach my $rowref (@$refAoA) { print join(",",@$rowref),"\n"; } } __END__ Original array: 1,2,3,4,8 1,4,2,4,5 1,6,1,7,5 Maximum of each column... coordinates based on row 0..n, col 0..n Max of column index 0 is 1 at array index 0 Max of column index 1 is 6 at array index 2 Max of column index 2 is 3 at array index 0 Max of column index 3 is 7 at array index 2 Max of column index 4 is 8 at array index 0 Transposed array: 1,1,1 2,4,6 3,2,1 4,4,7 8,5,5

Replies are listed 'Best First'.
Re^2: how to loop through many arrays
by david_lyon (Sexton) on Jun 19, 2011 at 06:42 UTC

    This is incredible, thanks so much!