Re: efficient max() function from sort

Ramprasad A Padmanabhan wrote:
>
> I use sort to give the max of an array something like this 
> 
> -----
> my @z = qw(12 24 67 89 77 91 44 5 10);
> my $max = ((reverse sort{$a <=> $b} (@z))[0]);
> print "MAX = $max\n";
> -----------
> 
> but when I am interested only in a single max value, I need not sort the 
> entire array 

Eugh. Where did you get this from? Hit them hard; with spoons.

OK, let's look at what you've written and try to make it visible.

  my $max = ((reverse sort{$a <=> $b} (@z))[0]);

The parentheses around @z are superfluous are superfluous, so the inner call is

  sort {$a <=> $b} @z

Now that's cool - we're sorting an array numerically. Next?

  reverse sort {$a <=> $b} @z

Ouch. So we sort the contents of @z numerically into one list and then reverse
that list into a second. We could forget that reverse and just write

  sort {$b <=> $a} @z

but we didn't do that. Never mind. Next?

Oh. We take just the the first element of the reversed sorted list with

  (reverse sort {$a <=> $b} @z)[0]

So that's the maximum value. Fine. Now?

  (  (reverse sort {$a <=> $b} @z)[0]  )

Someone thought we needed a list, so put some parentheses round that value.

And finally

  my $max = (  (reverse sort {$a <=> $b} @z)[0]  );

Oh. So that one-element list is being evaluated in scalar context after all.

Here are my thoughts.

- It's ugly
- It does mountains of unnecessary work
- It doesn't look like it works
- Few people can explain why it works

What you meant was either

  $max = (sort {$a <=> $b} @z)[-1];

or

  use List::Util qw/max/;
  $max = max @z;

Big, hard spoons please.

Rob











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> 
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