if block inside map

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

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Re: if block inside map by choroba (Cardinal) on Nov 11, 2011 at 16:23 UTC
`@x = map { if ($_ > 1) { 1 } } (-5 .. 5)` [download] But trying to read your mind, I suppose you need rather `@x = map { if ($_ > 1) { 1 } else { 0 } } (-5 .. 5)` [download] which can be also written with the ternary operator: `@x = map { $_ > 1 ? 1 : 0 } (-5 .. 5)` [download]	[reply] [d/l] [select]
Re^2: if block inside map by Eliya (Vicar) on Nov 11, 2011 at 17:42 UTC
Just to elaborate a little. You can also leave off the else branch, in which case map would return the empty string (not sure why not `undef`) when the if-condition isn't true: `my @x = map { if ($_ > 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]	[reply] [d/l] [select]
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
Re^2: if block inside map by taiko (Sexton) on Dec 08, 2015 at 11:53 UTC
ouh man, you made my day with this. Specially with ternary operator	[reply]
Re^3: if block inside map by AnomalousMonk (Archbishop) on Dec 08, 2015 at 16:59 UTC
Other ways: If you can use empty strings instead of zeros in the output list (i.e., you're not doing arithmetic with the elements of the output), then either `map { $_ > 0 }` or just `map $_ > 0,` (note the terminating comma) will do the trick: `c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "my @x = map $_ > 1, -3 .. 3; dd \@x; " ["", "", "", "", "", 1, 1]` [download] If you gotta have 0s, `\|\|` or `or` will do: `c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "my @x = map { $_ > 1 or 0 } -3 .. 3; dd \@x; " [0, 0, 0, 0, 0, 1, 1]` [download] (Note that `map $_ > 1 \|\| 0, -3 .. 3` would also work, but `map $_ > 1 or 0, -3 .. 3` will not. Can you say why? This is one reason why some Best Practices recommend avoiding the `map EXPR, LIST` form of map.) And of course, there are other ways... Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re: if block inside map by Corion (Patriarch) on Nov 11, 2011 at 16:22 UTC
Have you looked at map? What parts of it do you have problems with? What else have you tried, and how did it fail?	[reply]