Summing different set of arrays.

 7  10  2001  24  10  5  14

 7  10  2001  14  15  2  1

 7  10  2001  14  13  2  9   =x

 31  3  2002  14  9  2  6

 1  4  2002  14  19  10  3

 1  4  2002  5  30  11  12

I have this table i would like to sum all the values in column 6 corresponding to the value 14 in column 4 for only the year 2002. So 14 appears twice in 2002 column 4 and the corresponding values are 2 and 10 in column 6 and their sum is 12. So i would like my answer to be 12. So far I've written

for x(:,3)==2002

    sum(x(x(:,4)==14, 6))
end

What would I need to change around to get the value i wanted of 12. Thank you

Answer 1

[C.J. Harris]

nYear  = 2002;
nValue = 14;

x = [7  10  2001  24  10  5  1
     7  10  2001  14  15  2  1
     7  10  2001  14  13  2  9
     31  3  2002  14  9  2  6
     1  4  2002  14  19  10  3
     1  4  2002  5  30  11  12];

   nResult = sum(x((x(:,3) == nYear) & (x(:,4) == nValue),6));

Answer 2

[Guillaume]

As in all likelyhood your criteria is going to change, I would calculate the sum for each unique combination of year column 4 all at once. This is easily achieved with unique and accumarray:

db = [7  10  2001  24  10  5  1
      7  10  2001  14  15  2  1
      7  10  2001  14  13  2  9
      31  3  2002  14  9  2  6
      1  4  2002  14  19  10  3
      1  4  2002  5  30  11  12];
keycolumns = [3, 4] %columns used as primary keys
valuecolumn = 6;   %column to sum
[keyval, ~, keyindex] = unique(db(:, keycolumns), 'rows')
dbsums = [keyval, accumarray(keyindex, db(:, valuecolumn))]

Answer 3

[TastyPastry]

There's no need to use a for loop for this job. In any case, you've incorrectly set up a for loop. you need a loop control variable and some vector which represents the values the loop control variable takes on as the loop executes. You have a boolean vector.

What I'd do is set up a mask using the && operator with two conditions: x(:,3) == 2002 and x(:,4) == 14. This will find all the values of x where the 3rd column is 2002 and 4th column is 14. Then I'd just use that mask and sum the 6th column using sum. You could do it in one line:

 sum(x(x(:,3)==2002&x(:,4)==14,6))