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position lists

• To: mathgroup at smc.vnet.net
• Subject: [mg68688] position lists
• From: "rych" <rychphd at gmail.com>
• Date: Wed, 16 Aug 2006 03:36:19 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

have
  In: a = {1, 1, 2, 2, 1, 4}
want
  {{1, 2, 5}, {3, 4}, {0}, {6}};

more effectively than just
  In: Position[a, #] & /@ Range[4]
  Out: {{{1}, {2}, {5}}, {{3}, {4}}, {}, {{6}}}

Ideas? Known one-liners?
Thanks
Igor

• Follow-Ups:
  • Re: position lists
    • From: János <janos.lobb@yale.edu>
  • Re: position lists
    • From: Sseziwa Mukasa <mukasa@jeol.com>