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n-dim array generator

by jo37 (Pilgrim)
on Jun 16, 2020 at 19:54 UTC ( #11118149=perlmeditation: print w/replies, xml ) Need Help??

Every now and then I need to create a n-dimensional array from some given formula, where n almost always is 1 or 2.
I've been searching for a module providing such functionality without success. It would be a surprise if there really wasn't such a thing.

But so I rolled my own and came to this:

# arg_1 to arg_n specify size in dimension k, # last arg is a reference to a sub # - expecting n arguments x1 ... xn # - returning the desired value at $na->[x1]...[xn] sub narray { my $size = shift; my $val = pop; my $na; for my $i (0 .. $size - 1) { $na->[$i] = @_ ? narray(@_, sub {&$val($i, @_)}) : &$val($i); } $na; }
which can be used in various ways and is not limited in dimension:
$ar = narray(3, sub {$_[0]}); # [0, 1, 2] $mr = narray(3, 3, sub {$_[0] == $_[1] || 0}); # [[1, 0, 0], [0, 1, 0], [0, 0, 1]]
just to get an idea.

Does anybody know of a module providing something similar?
Otherwise: Is this of use for someone else or would it even fit into something existing?

UPDATE 1: This would be more perlish if the sub ref argument came first and the sub itself was prototyped:

sub narray (&@); $ar = narray {$_[0]} 3;

UPDATE 2: Incorporating LanX's suggestion of using map into UPDATE 1 results in:

sub narray (&@); sub narray (&@) { my $val = shift; my $size = shift; [map {my $i = $_; @_ ? narray {&$val($i, @_)} @_ : &$val($i)} (0 . +. $size - 1)]; } my $na = narray {"<@_>"} 3, 2 # [['<0 0>', '<0 1>'], ['<1 0>', '<1 1>'], ['<2 0>', '<2 1>']]

Greetings,
-jo

$gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$

Replies are listed 'Best First'.
Re: n-dim array generator
by LanX (Cardinal) on Jun 17, 2020 at 13:01 UTC
    TIMTOWTDI

    I'm also showing the classic hard-coded approach with nested loops and auto-vivification for comparison.

    use strict; use warnings; use Data::Dump qw/pp dd/; use Test::More; sub matrix (&@){ my $code = shift; my $rec; my @coor; my $idx; $rec = sub { my $level = shift; return $code->(@coor) unless @_; my $max = shift; my $arr = [ map { $coor[$level] = $_; $rec->($level+1,@_) } 0 .. $max ]; return $arr; }; $rec->(0,@_); } my $a_matrix = matrix {"<@_>"} 3,2,1; my @classic; for my $x (0..3) { for my $y (0..2) { for my $z (0..1) { $classic[$x][$y][$z] = "<$x $y $z>"; } } } #pp \@classic; is_deeply($a_matrix,\@classic,"same matrix"); pp $a_matrix; done_testing;

    ok 1 - same matrix [ [ ["<0 0 0>", "<0 0 1>"], ["<0 1 0>", "<0 1 1>"], ["<0 2 0>", "<0 2 1>"], ], [ ["<1 0 0>", "<1 0 1>"], ["<1 1 0>", "<1 1 1>"], ["<1 2 0>", "<1 2 1>"], ], [ ["<2 0 0>", "<2 0 1>"], ["<2 1 0>", "<2 1 1>"], ["<2 2 0>", "<2 2 1>"], ], [ ["<3 0 0>", "<3 0 1>"], ["<3 1 0>", "<3 1 1>"], ["<3 2 0>", "<3 2 1>"], ], ] 1..1

    Cheers Rolf
    (addicted to the Perl Programming Language :)
    Wikisyntax for the Monastery

      The recursion can be simplified, since $level depends on the length of the remaining dimensions in @_.

      I also used a "fancy" trick with $cursor as ref to the @coor array.

      (EDIT: Of course there is still more room for improvement, it depends if clarity or speed matters)

      use strict; use warnings; use Data::Dump qw/pp dd/; use Test::More; sub matrix2 (&@){ my $code = shift; my @coor; my $depth = @_; my $rec; $rec = sub { return $code->(@coor) unless @_; my $level = $depth - @_; my $max = shift; my $cursor = \$coor[$level]; my $arr = [ map { $$cursor = $_; $rec->(@_) } 0 .. $max ]; return $arr; }; $rec->(@_); } my $a_matrix = matrix2 {"<@_>"} 3,2,1; my @classic; for my $x (0..3) { for my $y (0..2) { for my $z (0..1) { $classic[$x][$y][$z] = "<$x $y $z>"; } } } is_deeply($a_matrix,\@classic,"same matrix"); pp \@classic; done_testing;

      ok 1 - same matrix [ [ ["<0 0 0>", "<0 0 1>"], ["<0 1 0>", "<0 1 1>"], ["<0 2 0>", "<0 2 1>"], ], [ ["<1 0 0>", "<1 0 1>"], ["<1 1 0>", "<1 1 1>"], ["<1 2 0>", "<1 2 1>"], ], [ ["<2 0 0>", "<2 0 1>"], ["<2 1 0>", "<2 1 1>"], ["<2 2 0>", "<2 2 1>"], ], [ ["<3 0 0>", "<3 0 1>"], ["<3 1 0>", "<3 1 1>"], ["<3 2 0>", "<3 2 1>"], ], ] 1..1

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery

        Sure, there are several ways to implement it. That's not what I'm actually interested in - from the usage point of view it doesn't matter too much. Such a piece of code is just not enough that would justify it's own module. If only any of these were available as an export!

        Greetings,
        -jo

        $gryYup$d0ylprbpriprrYpkJl2xyl~rzg??P~5lp2hyl0p$
      and here a variation using a for-loop instead of a map, probably easier to grasp:

      use strict; use warnings; use Data::Dump qw/pp dd/; use Test::More; sub matrix3 (&@){ my ($code,@dims) = @_; my @coor =(undef)x@dims; my $rec; $rec = sub { my @dims =@_; return $code->(@coor) unless @dims; my $level = - @dims; my $max = shift @dims; my $cursor = \$coor[$level]; my @arr; for ( 0 .. $max ) { $$cursor = $_; $arr[$_] = $rec->(@dims); } return \@arr; }; return $rec->(@dims); } my $a_matrix = matrix3 {"<@_>"} 3,2,1; my @classic; for my $x (0..3) { for my $y (0..2) { for my $z (0..1) { $classic[$x][$y][$z] = "<$x $y $z>"; } } } is_deeply($a_matrix,\@classic,"same matrix"); pp \@classic; done_testing;

      Cheers Rolf
      (addicted to the Perl Programming Language :)
      Wikisyntax for the Monastery

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