How to find the index of splitapply

4 views (last 30 days)
I have this code where I split the data into intervals and I look to find the maximum value for each interval as below. I need to find the indexes of the maximum values (Result) as well to collect more information from the original matrix (data). For simplify I created the following example.
x = round(Data(:,18),0);
y = Data(:,17);
[uv,~,idx] = unique(x);
[Result] = splitapply(@max, y, idx);
How can I find the indexes correspond to the Result to get more information from the original data.
Thank you so much for your help.

Accepted Answer

Matt J
Matt J on 29 Apr 2019
Edited: Matt J on 29 Apr 2019
The indices within each group or the indices over all of y? If the former,
indices = splitapply(@maxIndex, y, idx);
function out=maxIndex(z)
[~,out]=max(z);
end
  7 Comments
Matt J
Matt J on 30 Apr 2019
Edited: Matt J on 30 Apr 2019
That is why I asked you at the beginning if you meant, "The indices within each group or the indices over all of y?" If you meant the former, then your first set of results is correct. For example, if I extract all the YY for which idx==1, I obtain,
group=[10,30]
and clearly the maximum over the group occurs at the second element, so indices=2 is the correct output.
However, since It is now clear that you meant "the indices over all of y", here is the solution for that,
XX = [1 2 3 4 5 1 3].';
YY = [10 10 10 20 20 30 20].';
[uv,~,idx] = unique(XX,'stable');
II=(1:numel(XX)).';
S = splitapply(@(xy)maxIndex(xy), [II,YY], idx);
[Result,indices]=deal(S(:,1),S(:,2))
m = [uv, Result, indices]
function out=maxIndex(xy)
[ymax,loc]=max(xy(:,2),[],1);
out=[ymax,xy(loc,1)];
end
Yaser Khojah
Yaser Khojah on 30 Apr 2019
Dear Matt J thanks a lot for your help and that helps a lot :)

Sign in to comment.

More Answers (0)

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!