# Find elements from a matrix and sum variables from other matrix

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nlm on 9 Feb 2019
Commented: nlm on 10 Feb 2019
Hi,
I have a matrix of lat long (406, 964) say A, and B. I also have a huge matrix of length 36000 and 3 variables (lat, long, intensity), say C. The lat lon in C have repeated values. I need to find only the elements of A and B that match in C, but also sum the intensity values of all those matching coordinates.
Thank you. Look forward to you help.
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### Accepted Answer

Matt J on 9 Feb 2019
T=array2table(C);
Gs = groupsummary(T,{'C1','C2'},@sum);
Gs = table2array(Gs(:,[1,2,4]));
bool=ismember(Gs(:,1),A) & ismember(Gs(:,2),B);
result=Gs(bool,:),
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nlm on 10 Feb 2019
I have a matrix of lat lon count, where for same lat lon, the count variable range between 1 to 4.
I need to have something like this,
LAT LON cnt = 1 cnt=2 cnt=3 cnt =4
12.4 91.4 1 0 3 0
31.4 45.6 2 4 0 9
45.9 91.5 10 0 9 20
I tried table, I could not figure out.

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### More Answers (1)

Matt J on 9 Feb 2019
Na=numel(A);
Nb=numel(B);
[~,Ia]=ismember(C(:,1),A(:));
[~,Ib]=ismember(C(:,2),B(:));
result = accumarray([Ia,Ib],C(:,3),[Na,Nb]);
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nlm on 9 Feb 2019
This issued an error,
"Error using accumarray
Requested 391384x391384 (1141.3GB) array exceeds maximum array size preference."

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