[kw-pm] unique

[John Macdonald]

On Wed, Apr 19, 2006 at 05:22:50AM -0600, Dave Carr wrote:
> Found this snippet to do unique on a sorted array
> 
>  
> 
> $prev = 'nonesuch';
> 
> @uniq = grep($_ eq $prev && (($prev) = $_), @sorted);
> 
>  
> 
> How could I modify this to require a string to occur at least two times
> to be included in the output array, in other words single occurrences
> will be skipped?

You've already noted that the 'eq' needs to be 'ne' for
that code to work.


$prev = 'nonesuch';
$count = 0;
$min_count = 2;

@multiples = grep {
		$_ eq $prev
		    ?? ( ++$count == $min_count )
		    :: ( ($prev = $_), ($count = 0) )
		} @sorted;

That selects elements that have been seen exactly $min_count
times, so it skips elements that are not repeated that many
time, and only returns one copy of an element that occur
more times.

If you set $min_count to 1, it returns the unique elements as
before (but with a bit more processing overhead), if you set
it to a larger number, you can select a unique copy of every
element that occurs at least $min_count times.

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