# Cumulative Summation down a matrix in loop

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IDN on 9 Feb 2022
Commented: Adam Danz on 10 Feb 2022
Hello!
I have 2 matrix, I would like to sum Matrix B values cummulative given condition. The condition is that it starts to sum once Matrix A = -1 and stops when Matrix A = 1 and it goes on and on all the way down to the end of the data set. Thanks for the help!
Matrix A Matrix B CumSum
0
0
0
-1 0
-1 0.02
-1 -12.09
-1 6.61
1 1.1 -4.36 CumSum
0 0
-1 0
-1 -6.8
-1 -26.87
-1 2.67
-1 -9.99
-1 9.28
-1 -3.17
1 8.6 7.39 CumSum
0
0
0
##### 2 CommentsShowHide 1 older comment
IDN on 9 Feb 2022
those are the totals when cumum runs by summing values in Matrix B. So -4.36 and -26.28 is the expected answer when all set an done. Thanks for helping!

Adam Danz on 9 Feb 2022
Edited: Adam Danz on 9 Feb 2022
If and only if the groups marked by A=-1 to A=1 are not interruped by any other values in A and a 1 does not appear before the first -1, the solution is,
Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.
T = 20×3 table
MatrixA MatrixB CumSum _______ _______ ______ 0 NaN NaN 0 NaN NaN 0 NaN NaN -1 0 NaN -1 0.02 NaN -1 -12.09 NaN -1 6.61 NaN 1 1.1 -4.36 0 0 NaN -1 0 NaN -1 -6.8 NaN -1 -26.87 NaN -1 2.67 NaN -1 -9.99 NaN -1 9.28 NaN -1 -3.17 NaN
startIdx = find([false;diff(T.MatrixA==-1)==1]);
stopIdx = find([false;diff(T.MatrixA==1)==1]);
groupSums = arrayfun(@(start,stop)sum(T.MatrixB(start:stop)),startIdx,stopIdx)
groupSums = 2×1
-4.3600 -26.2800
Or perhaps you want,
T.CumSum(stopIdx) = groupSums
T = 20×3 table
MatrixA MatrixB CumSum _______ _______ ______ 0 NaN NaN 0 NaN NaN 0 NaN NaN -1 0 NaN -1 0.02 NaN -1 -12.09 NaN -1 6.61 NaN 1 1.1 -4.36 0 0 NaN -1 0 NaN -1 -6.8 NaN -1 -26.87 NaN -1 2.67 NaN -1 -9.99 NaN -1 9.28 NaN -1 -3.17 NaN
Adam Danz on 10 Feb 2022
Just saw your message now. Glad you worked it out. That line merely places data within the table T so nothing should be coming out horizontally.

Highphi on 9 Feb 2022
matrixA = [0 0 0 -1 -1 -1 -1 1 0 -1 -1 -1 -1 -1 -1 -1 1 0 0 0]'; % for ref
matrixB = [0 0 0 0 0.02 -12.09 6.61 1.1 0 0 -6.8 -26.87 2.67 -9-99 9.28 -3.17 8.6 0 0 0]'; % for ref
state = 0;
matrixSums = zeros(size(matrixA,1), 1);
for i = 1:size(matrixA, 1)
temp = matrixA(i);
if (temp == -1) && (state == 0)
state = 1;
cumSum = matrixB(i);
elseif (state == 1) && (temp ~= 1)
cumSum = cumSum + matrixB(i);
elseif (state == 1) && (temp == 1)
cumSum = cumSum + matrixB(i);
matrixSums(i) = cumSum;
state = 0;
end
end
outMat = [matrixA, matrixB, matrixSums]
outMat = 20×3
0 0 0 0 0 0 0 0 0 -1.0000 0 0 -1.0000 0.0200 0 -1.0000 -12.0900 0 -1.0000 6.6100 0 1.0000 1.1000 -4.3600 0 0 0 -1.0000 0 0
##### 2 CommentsShowHide 1 older comment
Highphi on 9 Feb 2022
you shouldn't need a toolbox, it's just a variable to indicate your status

R2020a

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