```Date: May 23, 2013 3:55 AM
Author: Bob Hanlon
Subject: Re: Average the same elements of the list

data = {{{a1, b1, c1}, d1}, {{a2, b2, c2}, d2},   {{a1, b1, c1}, d3}, {{a2, b2, c2}, d4},   {{a1, b1, c1}, d5}, {{a3, b3, c3}, d7}};For v7 and latersol = Plus @@ #/Length[#] & /@  GatherBy[data, First]{{{a1, b1, c1}, (1/3)*(d1 + d3 + d5)},   {{a2, b2, c2}, (d2 + d4)/2}, {{a3, b3, c3}, d7}}or (probably faster for longer lists)sol == ({#[[1, 1]], Mean[#[[All, 2]]]} & /@   GatherBy[data, First])TrueFor v3 or latersol == (Plus @@ #/Length[#] & /@   Split[data // Sort, #1[[1]] == #2[[1]] &])TrueBob HanlonOn Wed, May 22, 2013 at 2:18 AM, BBabic <bipsich101@gmail.com> wrote:> Hello,> I have list which is something like> data={> {{a1,b1,c1},d1},{{a2,b2,c2},d2}}> I would like to get new list which gets average of the second elements if> the first elements in the sublists are all the same.> Namely if a1=a2,b1=b2,c1=c2> new list would look like> datanew={{a1,b1,c1},Mean[{d1,d2}]> Is there an elegant way to do this ?> Thanks!>>
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