In the rightmost map,

map  { [$_, ($_ eq $first ? '' : $_)] } keys %$test;

The keys in %$test are converted to a list of arrays - [ key, key ], but with the `first' key having null for the second member of the array. (which will sort first with cmp).

Then, (s)he is then sorting by the second key, which will put the `first' key at the front:

sort { $a->[1] cmp $b->[1] }

If you want a string sort to ignore case, you should change this part to something like this:

sort {  ( lc($a->[1]) cmp lc($b->[1]) )
     or (    $a->[0]  cmp    $b->[0]  ) }
[download]

So in general we compare the keys converted to lower case. Strictly speaking, this is all you need to do. The second comparison (which will only be tested if the first comparison returns 0, or equal) compares the raw keys directly. This is just to make the code a little more orderly, so you can expect it to return a consistent ordering of, eg `Case' and `case'.

So, to answer your question - the leftmost map statement is a no-op, however I suspect the coder may have intended to do this:

my @list = map { $_->[0] } ...

Then @list would be filled with the actual keys. Then it would be a correct Schwarzian transform.

Here is a much quicker and more efficient approach to sort a list and keep a key first:

my @list = sort { ( ($b eq $first) <=> ($a eq $first) )
               or (    lc($a)      cmp     lc($b)     )
               or (       $a       cmp        $b      ) }
           keys %$hash;
[download]

This gets rid of the need for all of those temporary anonymous arrays.

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