MATLAB: Please your help is needed. I have the following 3-D array and would like to sum the values in second column and the third column based on their index values in frist column.

Question

          % |Bus | PGi | QGi | 
 M =        [1     10       0;
             1     10       0;
             1     76    14.1; 
             1     76    14.1;
             2     10       0;
             2     10       0;
             2     76     7.0;
             2     76     7.0;
             7     80    17.2;
             7     80    17.2;
             7     80    17.2;
            13   95.1    40.7;
            13   95.1    40.7;
            13   95.1    40.7;
            15     12       0;
            15     12       0;
            15     12       0;
            15     12       0;
            15     12       0;
            15    155    0.05;
            16    155   25.22;
            18    400   137.4;
            21    400   108.2;
            22     50   -4.96;
            22     50   -4.96;
            22     50   -4.96;
            22     50   -4.96;
            22     50   -4.96;
            22     50   -4.96;
            23    155   31.79;
            23    155   31.79;
            23    350   71.78];

Answer 1

Since you've got some sort of label attached to the 3 columns of your array, another option to Stephen's answer is to convert the array to a table which is ideally suited for this:

t = array2table(M, 'VariableNames', {'Bus', 'Pgi', 'QGi'})

It is then trivial to calculate the sum per Bus:

varfun(@sum, t, 'GroupingVariables', 'Bus')  %apply sum to each variable of the table, grouping by 'Bus'