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compress lists with mean for equal elements

• To: mathgroup at smc.vnet.net
• Subject: [mg100987] compress lists with mean for equal elements
• From: vJD <ephorie at gmail.com>
• Date: Fri, 19 Jun 2009 20:46:40 -0400 (EDT)

I have a nested list of this form:

{{{1, 13}, 97.6493}, {{1, 13}, 97.9511}, {{1, 14}, 99.3002}, {{1, 14},
99.4602}, {{1, 14}, 99.6193}, {{1, 15}, 100.513}, {{1, 15}, 101.149},
{{1, 15}, 101.483}, {{1, 15}, 101.494}, {{1, 16}, 101.51}, {{1, 16},
101.895}}

I want to shrink the list in the way that I calculate the mean over
the second part for all elements where the first part is equal. so
e.g. the first element of the new list will be {{1,13}, 97.8002},
because they both have {1,13} and the mean of 97.6493 and 97.9511 is
97.8002.

The problem is that there is no fixed number for the equal elements
(so e.g. two elements with {1,13}, three elements with {1,14} and so
on). The number is random.

Can anybody please provide me with a statement or hint how to
accomplish that task.

Thank you very much

Regards,
Holger

• Follow-Ups:
  • Re: compress lists with mean for equal elements
    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>