Re: Howto sum up a list?
- To: mathgroup at smc.vnet.net
- Subject: [mg106961] Re: Howto sum up a list?
- From: Bill Rowe <readnews at sbcglobal.net>
- Date: Fri, 29 Jan 2010 07:49:01 -0500 (EST)
On 1/28/10 at 2:43 AM, news at jonasstein.de (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}
In[1]:= myList = {{eggs, 4}, {milk, 1}, {eggs, 1}, {milk, 1}};
In[2]:= {#[[1, 1]], Total[#[[All, 2]]]} & /@ GatherBy[myList, First]
Out[2]= {{eggs, 5}, {milk, 2}}