List Operations

*To*: mathgroup at smc.vnet.net*Subject*: [mg65681] List Operations*From*: "LectorZ" <lectorz at mail.ru>*Date*: Fri, 14 Apr 2006 04:32:05 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

Hi guys, My question: mylist={{1,a, b},{1,a, b},{1,a, b},{2,b,z},{2,b,z},{2,b,z},{2,b,z},....,{n,x,y},{n,x,y},{n,x,y},...{n,x,y}} The sublists are of different length. I need to calculate the product between the 2nd and 3rd element of every sublist (e.g. a*b) and then add them up according to the 1st element: sum of all products where the 1st element is 1, 2, ...n. The result should be a list like that: {{1,a*b+a*b+a*b},{2,b*z+b*z+b*z+b*z}, ...,{n, x*y+x*y+x*y+...+x*y}} Thank you for your help. LZ

**Follow-Ups**:**Re: List Operations***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>