Cumulative Summation down a matrix in loop

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

[Turlough Hughes]

Do you mean -4.36 and -26.28?

[IDN]

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!

Answer 1

[Adam Danz]

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,

 T = readtable('Sum Sample.xlsx')

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 

[IDN]

Perfect thanks!

[IDN]

One last question...T.CumSum(stopIdx) = groupSums comes out horizontally and transpose doesnt seem to work? how can i make it to go vertically?

[IDN]

Got it!

[Adam Danz]

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.

Answer 2

[Highphi]

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

[IDN]

Thanks, this looks good as well...i just dont have the toolbox required for the "state" functionality

[Highphi]

you shouldn't need a toolbox, it's just a variable to indicate your status