Re: Summing over like elements
- To: mathgroup at smc.vnet.net
- Subject: [mg13865] Re: [mg13855] Summing over like elements
- From: wself at viking.emcmt.edu (Will Self)
- Date: Wed, 2 Sep 1998 01:30:59 -0400
- Sender: owner-wri-mathgroup at wolfram.com
Mitch asks for the following:
>I have a 2 column array. Column 1 has some values, many of which are
>repeated. Column 2 has probabilities of these values.
>
>I would like to sum the probabilities for each unique element in column
>1. For example:
>
>{{1, .5} , {2, .2} , {1, .1}} should give me:
>
>{{1, .6} , {2, .2}}
Mitch, this will do it:
In[1]:= mm={{1, .5} , {2, .2} , {1, .1}}
Out[1]= {{1, 0.5}, {2, 0.2}, {1, 0.1}}
In[2]:= Function[x,{x,Plus@@(#[[2]]&/@Select[mm,#[[1]]==x&])}]/@
Union[#[[1]]&/@mm]
Out[2]= {{1, 0.6}, {2, 0.2}}
Will