It is often useful to implement algorithms using nested array operations. For example, to find the number of words in a list that start with each given character, you might do something like this in Python:
>>> a = ["foo","bar","baz"]
>>> map(lambda c: len(filter(lambda w: w.startswith(c), a)), ('a','b','c','d','e','f'))
[0, 2, 0, 0, 0, 1]
In the expression w.startswith(c)
it is trivial to distinguish between the two loop iteration variables w
and c
because they have different names.
In Perl, I would like to do something like this:
@a = ("foo", "bar", "baz");
map length(grep $_ =~ /^$_/, @a), ('a','b','c','d','e','f')
However, the obvious problem with this is that $_
refers only to the innermost grep
iteration variable (suitable for the $_
on the left), not the one for the outer map
(suitable for the /^$_/
). What is the idiomatic way to avoid this problem in Perl?