Re^2: if block inside map

Just to elaborate a little. You can also leave off the else branch, in which case map would return the empty string (not sure why not undef) when the if-condition isn't true:

my @x = map { if ($_ > 0) { $_*2 } } (-2 .. 2);
use Data::Dumper;  print Dumper \@x;

__END__
$VAR1 = [
          '',
          '',
          '',
          2,
          4
        ];
[download]

When you don't want to return anything in those cases, you can use the empty list ():

my @x = map { if ($_ > 0) { $_*2 } else { () } } (-2 .. 2);
# or: my @x = map { $_ > 0 ? $_*2 : () } (-2 .. 2);
use Data::Dumper;  print Dumper \@x;

__END__
$VAR1 = [
          2,
          4
        ];
[download]

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Re^3: if block inside map by AnomalousMonk (Archbishop) on Nov 11, 2011 at 21:14 UTC
You can also leave off the else branch, in which case map would return the empty string (not sure why not undef) when the if-condition isn't true... (Emphasis added) See Re: Map Function Weirdness and Re: Map Function Weirdness (and ikegami's elaboration thereto Re^2: Map Function Weirdness) to Map Function Weirdness.	[reply]
Re^4: if block inside map by Eliya (Vicar) on Nov 11, 2011 at 23:57 UTC
Thanks for the pointer. I must admit that thread somehow happened to sneak out from under my radar :) Personally, I would consider it more "natural" if an if-construct without an else clause (when used in an "expression context") would sematically behave more like a ternary `cond ? ... : undef` (instead of `cond ? ... : cond`), but if you look at it from the perspective of what is evaluated last, it's of course perfectly clear why things behave as they do. (Yes, I'm aware that if-constructs in Perl - unlike in some other languages - don't evaluate to anything itself (as a whole), i.e. they are not expressions — so no need to comment on that.)	[reply] [d/l] [select]