Re: Howto sum up a list?

*To*: mathgroup at smc.vnet.net*Subject*: [mg106939] Re: [mg106913] Howto sum up a list?*From*: Fred Simons <f.h.simons at tue.nl>*Date*: Fri, 29 Jan 2010 07:45:03 -0500 (EST)*References*: <201001280743.CAA23521@smc.vnet.net>

Jonas Stein wrote: > How can i sum up the list: > > MyList = {{eggs, 4}, {milk, 1}, {eggs, 1}, {milk, 1}} > > I want to get something like: > > {{eggs, 5},{milk, 2}} > > I tyied Tally[], but that ignored the factor 4 in {eggs, 4} > > Thank you. > > In this particular case, with each sublist consisting of a name and a number, the following can be used: List @@@ List @@ Times @@ Power @@@ MyList More general is {#[[1, 1]], Total[#[[All, 2]]]} & /@ SplitBy[Sort[MyList], First] Kind regards, Fred Simons Eindhoven University of Technology

**References**:**Howto sum up a list?***From:*Jonas Stein <news@jonasstein.de>