我有一个这样的矩阵：
>>D=[1,0,10;3,1,12;3,1,12.5;6,1,6;6,2,11.1;]
D =
1.0000 0 10.0000
3.0000 1.0000 12.0000
3.0000 1.0000 12.5000
6.0000 1.0000 6.0000
6.0000 2.0000 11.1000
如果它们的第一列相同，我想获得第二列数据的总和。例如，我想要：
E=
1.0000 0
3.0000 2.0000
6.0000 3.0000
所以我尝试了
b = accumarray(D(:,1),D(:,2),[],[],[],true);
[i,~,v] = find(b);
E = [i,v]
但它没有用。我应该怎么办？
Use a combination of unique and accumarray this way -
[unique_ids,~,idmatch_indx] = unique(D(:,1));
%// unique_ids would have the unique numbers from first column and only
%// used to get the first column of final output, E.
%// idmatch_indx are tags put on each element corresponding to each unique_ids
%// based on the uniqueness
%// Accumulate and perform summation of elements from second column of D using
%// subscripts from idmatch_indx
E = [unique_ids accumarray(idmatch_indx,D(:,2))]
With accumarray you are generally required to input the function that you would like to use on the accumulated elements, but @sum being the default function handle, you can it leave out for this case.