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











Is there a more efficient alternative to this

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