Sum elements in a list with conditions

*To*: mathgroup at smc.vnet.net*Subject*: [mg128422] Sum elements in a list with conditions*From*: Guillermo Sanchez <guillermo.sanchez at hotmail.com>*Date*: Thu, 18 Oct 2012 02:36:46 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

I have a list of sublist of pairs. I wish sum the second elements of the sublists when the first elements are equals Example: Int[]:={{1, a}, {2, b}, {1, c}, {2, d}, {2, e}, {3, f}} I hope Out[]:= {{1, a + c}, {2, b + c + e}, {3, f}} I can do it as is it is shown below but could any body find and easier solution. list1 = {{1, a}, {2, b}, {1, c}, {2, d}, {2, e}, {3, f}}; list2 = GatherBy[list1, First]; {l1, l2} = Transpose[Plus @@@ GatherBy[list, First]]; Transpose[{l1/Length /@ list2 , l2}]

**Follow-Ups**:**Re: Sum elements in a list with conditions***From:*Adriano Pascoletti <adriano.pascoletti@uniud.it>

**Re: Sum elements in a list with conditions***From:*Fred Simons <f.h.simons@tue.nl>

**Re: Sum elements in a list with conditions***From:*Bob Hanlon <hanlonr357@gmail.com>

**Re: Sum elements in a list with conditions***From:*Sseziwa Mukasa <mukasa@gmail.com>