Summing list subsets
- To: mathgroup at smc.vnet.net
- Subject: [mg30711] Summing list subsets
- From: "Mark Coleman" <mcoleman at bondspace.com>
- Date: Sat, 8 Sep 2001 02:55:38 -0400 (EDT)
- Organization: BondSpace, Inc.
- Sender: owner-wri-mathgroup at wolfram.com
Greetings:
Consider two lists:
x = {a,a,b,b,b,b,c,d,d,d,d,d,} and y = {1,1,2,2,2,2,3,4,4,4,4,4}
I would like to have a function that returns the sum (or any other function)
of each unique element of x, given the corresponding value in y. That is,
for a 'Sum', the result would be
z={{a,2},{b,8},{c,3},{d,20}}
This is similar in spirit to a common database aggregation problem.
Any ideas?
Thanks.
-Mark