Many of us have written (and posted) code to build a "prefix" hash (a.k.a Trie indexes), but I wanted a quick command line to do this for word tokens over a set of short phrases. Allowing that Data::Dumper output would suffice, the solution was pretty short. (updated to fix the link to CPAN)
perl -MData::Dumper -lne '$i=\%h; for(split){$$i{$_}{N}++; $i=$$i{$_}}
 END{print Dumper(\%h)}'

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Re: One-liner to build a Trie
by graff (Chancellor) on Oct 30, 2007 at 06:00 UTC
    To elaborate a bit: the task was to look for frequent patterns in headlines of news articles, in hopes of identifying repetitive daily (hourly, weekly) reports that would tend to have formulaic content -- i.e. to isolate groups of headlines like: 
    TOP STORIES FOR WEDNESDAY, JUNE 14
TOP STORIES FOR TUESDAY, JULY 27
...
STOCK INDEXES, NYSE 11:00 GMT
STOCK INDEXES, NASDAQ 13:00 GMT
...
BASEBALL: FINAL SCORES ...
...

    [download]
    Those are made-up examples, but you get the idea: find bunches of headlines in a multi-year archive that start with the same words. Of course, the same code (with a different split regex) would create the more typical character-based trie structure.
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