Comments on: Nested Maps in Perl

By: tajuma

tajuma — Thu, 07 Jun 2012 10:08:40 +0000

Ouch, something ate half of the perl code in my previous comment, new try

map { &{ sub { map { $_[0] . $_ } qw(a b c d e) } }($_) } (1..5)

By: tajuma

tajuma — Thu, 07 Jun 2012 09:59:49 +0000

You can pass the outer $_ as a parameter to the inner map put inside a sub, and then refer the outer $_ in the inner as $_[0]:

map { qw(a b c d e) } }($_) } (1..5)

By: vol7ron

vol7ron — Tue, 10 Apr 2012 19:06:53 +0000

my $x = { map { $t->[0]->[$_] => $t->[1]->[$_] } 0..$#{$t->[0]} };
#hashref

By: vol7ron

vol7ron — Tue, 10 Apr 2012 19:04:47 +0000

my $t = [['a'..'e'],[1..5]]; my @x = map { $t->[0]->[$_] => $t->[1]->[$_] } 0..$#{$t->[0]}; There might be a better way than the above, but this is an alternative.

By: Using the diamond operator to find the Cartesian product of two lists. « Discovering Perl

Mon, 18 Oct 2010 21:00:27 +0000

[...] should go where they are due: I discovered this construct while reading juster’s comment on [...]

By: Jared

Jared — Wed, 06 Oct 2010 21:33:55 +0000

Hey juster, I knew about this trick in shell, but I didn't know it worked in perl's glob. And it's portable too!

$ c:/strawberry/perl/bin/perl test-juster.pl 
a1a2a3a4a5b1b2b3b4b5c1c2c3c4c5d1d2d3d4d5e1e2e3e4e5
$

By: Naveed Massjouni

Naveed Massjouni — Tue, 05 Oct 2010 02:29:25 +0000

@juster, that is very clever

By: juster

juster — Mon, 04 Oct 2010 21:34:32 +0000

I know this isn’t exactly what you asked for but I found this interesting when I discovered this feature of glob:

my @x = glob( ‘{a,b,c,d,e}{1,2,3,4,5}’ );

Hehe!

By: Jared

Jared — Mon, 04 Oct 2010 14:17:55 +0000

@Naveed – oh yes, the inner map is inside the outer map’s lexical scope so it is possible to my declare the variable inside the map. That makes it a lot neater already.

@zloyrusskiy – The $_{first}, $_{second}, etc… from List::Gen looks like a good generalisation of the technique I presented in my post. It would be nice if it was available in core Perl.

By: zloyrusskiy

zloyrusskiy — Mon, 04 Oct 2010 06:49:14 +0000

You can look at List::Gen module, it has mapkey() and cartesian() functions for that.

I think that Perl needs thats feature in future.