How to do a group by in matlab
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Hi, I have the following data:
data=[10 1 2 3; 11 4 5 6;10 0 20 30; 11 4 5 6; 12 7 8 9; 17 40 50 60]
I want to look for:
lookfor=[10;11]
and get the following result:
anwser=[10 1 22 33; 11 8 10 12]
So it's a group by...
I'm looking for a dynamic anwser, data matrix and lookfor matrix will vary and be much more bigger.
thank you in advance for your precious anwsers.
댓글 수: 2
Azzi Abdelmalek
2013년 5월 26일
편집: Azzi Abdelmalek
2013년 5월 26일
It's grouped by what? how did you get 1,22 and 33?
채택된 답변
Azzi Abdelmalek
2013년 5월 26일
편집: Azzi Abdelmalek
2013년 5월 26일
data=[10 1 2 3; 11 4 5 6;10 0 20 30; 11 4 5 6; 12 7 8 9; 17 40 50 60]
lookfor=[10;11];
a=arrayfun(@(x) data(find(data(:,1)==x),:),lookfor,'un',0);
b=cell2mat(cellfun(@(x) [x(1) sum(x(:,2:end),1)],a,'un',0))
%or
data=[10 1 2 3; 11 4 5 6;10 0 20 30; 11 4 5 6; 12 7 8 9; 17 40 50 60]
lookfor=[10;11]
for k=1:numel(lookfor)
ii=data(ismember(data(:,1),lookfor(k)),:);
res(k,:)=[ii(1,1) sum(ii(:,2:end))];
end
res
댓글 수: 9
Azzi Abdelmalek
2013년 5월 27일
편집: Azzi Abdelmalek
2013년 5월 27일
You should clear the variable res
clear res
% or better, pre-allocate
res=zeros(numel(lookfor),size(data,2))
추가 답변 (2개)
Andrei Bobrov
2013년 5월 27일
[i1,i2] = ismember(data(:,1),lookfor);
d2 = data(i1,2:end);
[j1,j2] = ndgrid(i2(i1),1:size(d2,2));
anwser = [lookfor,accumarray([j1(:),j2(:)],d2(:))];
댓글 수: 0
Lola Davidson
2024년 6월 3일
For those still stumbling on this, MATLAB now has several more functions to help with grouping workflows, including groupsummary and pivot.
For this problem, if you are expecting several different lookfor values on the same dataset, it may be faster to compute all the sums with groupsummary in one go:
[sums,grps] = groupsummary(data(:,2:end),data(:,1),"sum");
out = [grps sums]
On the other hand, if you only want to compute a small subset of the grouped sums per dataset, it may be quicker to filter down with ismember first, as others have mentioned.
idx = ismember(data(:,1),lookfor);
[sums,grps] = groupsummary(data(idx,2:end),data(idx,1),"sum");
out = [grps sums]
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