Re: Howto sum up a list?
- To: mathgroup at smc.vnet.net
- Subject: [mg106970] Re: [mg106913] Howto sum up a list?
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Fri, 29 Jan 2010 07:50:39 -0500 (EST)
- Reply-to: hanlonr at cox.net
myList = {{eggs, 4}, {milk, 1}, {eggs, 1}, {milk, 1}}; {#[[1, 1]], Total[#[[All, 2]]]} & /@ GatherBy[myList, First] {{eggs, 5}, {milk, 2}} {#, Total[Cases[myList, {#, n_} :> n]]} & /@ Union[myList[[All, 1]]] {{eggs, 5}, {milk, 2}} myList //. {s___, {t_, j_}, m___, {t_, k_}, e___} :> {s, {t, j + k}, m, e} {{eggs, 5}, {milk, 2}} Bob Hanlon ---- Jonas Stein <news at jonasstein.de> 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. -- Jonas Stein <news at jonasstein.de>