Re: [PHP] Number of duplicates in an array?

2008/8/18 tedd <tedd@sperling.com>:

> Anyone have a cool method of finding duplicate items in an array and the
> number of times they appear?
>
> I'm doing it in a way that is probably less than optimum. I want to see how
> you guys solve it.

Hmm. Assuming the following inputs and outputs:

$input_array = array( 'one', 'two', 'three', 'one', 'two', 'one' );
$output_array = array( 'one' => 3, 'two' => 2, 'three' => 1 );

$input_array = array( 'one', 'two', 'three', 'one', 'two', 'one' );
$output_array = array();
foreach( $input_array as $input )
{
if ( !isset( $output_array[$input] ) )
{
$output_array[$input] = 0;
}
$output_array[$input]++;
}

Untested code.

From a CompSci PoV, input_array is a list while output_array would be
better implemented as a binary tree (with the normal caveats about
tree balancing). But given that we're working in PHP and your data
sets probably aren't that large, this is the "good enough" solution.

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