You don't ave an else part. Use an empty list, and it'll work. 
my @someFruit = map { if ($_ =~ m/^[ap]/) { $_;} else { (); } } @allFr
+uit;

[download]
I now get: 
no. of some fruit: 2
some fruit: apple*apricot
Just to show you that it can be made to work. I'm not sure what is inserted in your version, I would have though of undef, but I get no warnings, so likely it's a boolean false (0 as number and "" as string), same value as !1 returns.

For this particular application, it would be wiser to use grep, but you could have used ? : too. And there's no need for the $_ =~. (Or the m.) 

my @someFruit = map { m/^[ap]/ ? $_ : () } @allFruit;

[download]
my @someFruit = grep { m/^[ap]/ } @allFruit;

[download]

In reply to Re: Extracting subset from list: map unsuitable? by bart
in thread Extracting subset from list: map unsuitable? by loris

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