# $Id: README,v 2.4 2011/09/14 16:35:05 ksb Exp $

Only unique elements (oue) is a filter that represents the
common perl idiom where we touch a key in a hash for each
element to "next" a loop to avoid duplicate processing.

This has a clear advantage over "sort -u", we start working on
the first element almost immediately.  It also has some very clever
uses in an xapply pipe-line.

$ data-source | oue | xapply -f 'template' -
The obvious one, process only the unique input items, less obvious
is that is starts almost as soon as "data-source" outputs the first
line.

$ data-source | xapply -f -P5 -m 'template' - | oue
Still pretty obvious, only output the unique results.

$ MY_HASH=/tmp/$$.$((RANDOM%100))
$ export MY_HASH
$ oue -D $MY_HASH /dev/null
$ data-source | xapply -P7 'template | oue -D$MY_HASH' -
$ rm $MY_HASH

A little less obvious, we lock the common tied-hash before we update it,
so this only outputs unique elements, but from any of the 7 xapply
children in some order.  Some applications might put the '-m' in the xapply
flags (I would).

In ksh you can use oue as a co-process, if you are careful.

--
ksb, Sep 2011, xapply@ksb.npcguild.org