Perl For loops

d2caetano has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Perl For loops by ikegami (Patriarch) on Jul 03, 2007 at 21:14 UTC
`my @array = map { STMT* EXPR } LIST;` [download] can be written as `my @array; for (LIST) { STMT* push @array, EXPR; }` [download] and `my @array = grep EXPR, LIST;` [download] can be written as `my @array; for (LIST) { if (EXPR) { push @array, $_; } }` [download]	[reply] [d/l] [select]
Re: Perl For loops by Util (Priest) on Jul 03, 2007 at 21:08 UTC
Untested, and probably completely wrong due to lack of `<CODE>...</CODE>` tags in the OP: `my @matrix = ( [ qw( 1 2 4 4 ) ], [ qw( 5 2 0 8 ) ], [ qw( 9 10 11 12 ) ], ); my @t; foreach my $column_num ( 0 .. $#{ $matrix[0] } ) { my @slice = map { $_->[$column_num] } @matrix; my @r; foreach my $n ( @slice ) { last if $n == 0; push @r, $n; } push @t, [@r]; }` [download]	[reply] [d/l] [select]
Re: Perl For loops by cdarke (Prior) on Jul 03, 2007 at 20:28 UTC
Why? What are you trying to achieve? It would help for readability if you used code tags. map returns a new list, whereas for allows modification of an existing one. You need to take the input list in your map and use that as the for list. You then need to push your result onto the output array. But if your code works, then why rewrite it to use for?	[reply]
Re^2: Perl For loops by naikonta (Curate) on Jul 04, 2007 at 01:48 UTC
map returns a new list, whereas for allows modification of an existing one It sounds like contracdicting although, perhaps, you didn't mean it. The map operator allows modification as well since `$_` would be a reference to the corresponding elements of existing array. `$ perl -wle 'my @ar = qw(one two three); print "@ar"; my @new = map { +$_ = uc } @ar; print "@new"; print "@ar"' one two three ONE TWO THREE ONE TWO THREE` [download] Open source softwares? Share and enjoy. Make profit from them if you can. Yet, share and enjoy!	[reply] [d/l] [select]
Re^3: Perl For loops by cdarke (Prior) on Jul 04, 2007 at 10:42 UTC
True. Apologies.	[reply]
Re: Perl For loops by aufflick (Deacon) on Jul 04, 2007 at 06:41 UTC
This code doesn't need to be so complicated - for instance why is there an `and` in there? If the values are always simple integers then the whole $z thing is just testing for equality with 0. Given that, the loop is just aborting once a 0 values is hit. We also know that the length of the outer array in the result is the count of the first inner array in the matrix. Thus: `my @matrix=([qw(1 2 4 4)],[qw(5 2 0 8)],[qw(9 10 11 12)],); my @t; for my $i (0..$#{$matrix[0]}) { for my $j (0..$#matrix) { last if $matrix[$j][$i] == 0; $t[$i][$j] = $matrix[$j][$i]; } }` [download] The result of both your code and mine is the same: `$VAR1 = [ [ 1, 5, 9 ], [ 2, 2, 10 ], [ 4 ], [ 4, 8, 12 ], ]` [download] Update: I must have missed Util's comment, which is virtually identical to mine :)	[reply] [d/l] [select]
Re^2: Perl For loops by atemon (Chaplain) on Jul 04, 2007 at 07:31 UTC
Hi Monks, I don't know what is the purpose of getting it in a "for" loop. But if we are concerned only about output or $t, can't we do something like `$t = [ @matrix ]` [download] so that the entire program would be `my @matrix=([qw(1 2 4 4)],[qw(5 2 0 8)],[qw(9 10 11 12)],); my $t = [ @matrix ];` [download] Or even simpler like `my $t = [ [qw(1 2 4 4)],[qw(5 2 0 8)],[qw(9 10 11 12)], ];` [download] cheers! -VC Update: Appologies for the carelessness & waste of time.	[reply] [d/l] [select]
Re^3: Perl For loops by aufflick (Deacon) on Jul 06, 2007 at 03:34 UTC
well, because your way $t is: `[ [ 1, 2, 4, 4 ], [ 5, 2, 0, 8 ], [ 9, 10, 11, 12 ], ]` [download] when it should be: `[ [ 1, 5, 9 ], [ 2, 2, 10 ], [ 4 ], [ 4, 8, 12 ], ]` [download] kinda different...	[reply] [d/l] [select]
Re: Perl For loops by toolic (Bishop) on Jul 03, 2007 at 20:53 UTC
Look at Writeup Formatting Tips for quick guidelines on how to post code.	[reply]