When I was learning map and grep, it helped me to see the equivalent of them in normal perl code.
my @a = map { transformation($_) } @b;
# same as
my @a;
push @a, tranformation($_) for @b;
@a
And
my @a = grep { condition($_) } @b;
# same as
my @a;
for (@b) {
push @b, $_ if condition($_);
}
@a
If you see yourself using one of those patterns, you can likely use map or grep instead.
And as a final note, you can use both without a block if you want to use only one expression:
my @even = grep $_ % 2 == 0, @numbers;
my @odd = map $_ * 2 +1, @numbers;
In particular that allows you to write
my @numbers = grep /^[0-9]+$/, @words;
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