array confusion

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

Hi, I have totally confused myself with arrays. I have an anon 2d array (arbitrary size) that looks like this:
$a = [[1,2,3],[4,5,6]...]
and I want it to transform it to look like this:
$b = [[1,2],[3],[4,5],[6]...]

Ok in formulating my question I think I solved it:

foreach $row (0..$#A){ #array row length
  foreach $col (0 .. ($#{$A[0]} - 1) ) { #array width less one
    $b->[$row*2][$col] = $a->[$row][$col]; # copy all but last ele ove
+r
  }
  $b->[($row *2) +1][0] = $a->[$row][$#{$A[0]}]; #now copy last
  #there are twice as many rows so we double the row index
}
[download]

Solved - but is there a neater way? Array slices? z

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Re: array confusion by jwkrahn (Abbot) on May 11, 2012 at 05:55 UTC
`$ perl -e' use Data::Dumper; my $A = [[1,2,3],[4,5,6]]; print Dumper $A; @$A = map { [ splice @$_, 0, 2 ], $_ } @$A; print Dumper $A; ' $VAR1 = [ [ 1, 2, 3 ], [ 4, 5, 6 ] ]; $VAR1 = [ [ 1, 2 ], [ 3 ], [ 4, 5 ], [ 6 ] ];` [download]	[reply] [d/l]
Re^2: array confusion by tobyink (Canon) on May 11, 2012 at 06:34 UTC
Personally I find `pop` a little more readable. `use Data::Dumper; my $A = [[1,2,3],[4,5,6]]; @$A = map { $_, [pop @$_] } @$A; print Dumper($A);` [download] `perl -E'sub Monkey::do{say$_,for@_,do{($monkey=[caller(0)]->[3])=~s{::}{ }and$monkey}}"Monkey say"->Monkey::do'`	[reply] [d/l] [select]
Re^2: array confusion by zerocred (Beadle) on May 11, 2012 at 05:58 UTC
Now that... is just ingenious. And extremely quick! Thanks!!	[reply]
Re: array confusion by BrowserUk (Patriarch) on May 11, 2012 at 06:04 UTC
Solved - but is there a neater way? Neater is in the eye of the beholder: `$a = [[1,2,3],[4,5,6],[1],[1..4],[1..5]];; $b = [ map{ my @x; push @x, [ shift(@$_),shift(@$_)//() ] while @$_; @ +x } @$a ];; pp $b;; [[1, 2], [3], [4, 5], [6], [1], [1, 2], [3, 4], [1, 2], [3, 4], [5]]` [download] Oh, for a mapwhile construct in Perl. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply] [d/l]
Re^2: array confusion by zerocred (Beadle) on May 11, 2012 at 07:18 UTC
Thanks - I really gotta bone up on use and abuse of 'map'.	[reply]
Re^3: array confusion by BrowserUk (Patriarch) on May 11, 2012 at 07:22 UTC
Outta interest. Did you mean to imply that all the subarray in the input had exactly 3 elements? Is modifying the input in-place okay? With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. The start of some sanity?	[reply]
Re^4: array confusion by zerocred (Beadle) on May 11, 2012 at 09:08 UTC