Sum elements in a list with conditions
- To: mathgroup at smc.vnet.net
- Subject: [mg69828] Sum elements in a list with conditions
- From: "Guillermo Sanchez" <guillermo.sanchez at hotmail.com>
- Date: Sat, 23 Sep 2006 23:45:50 -0400 (EDT)
Dear group
I have a pair of elements list. The second elements of the list should
be summed when the first element of the pairs are equals. Example
Given
{{a1, b1},{a2,b2},{a2,b3},{a2,b4},{a3, b5}, {a3, b6}}
the output should be
{{a1, b1},{a2, b2+b3+b4},{a3, b5+b6}}
Thanks
Guillermo