How do I get a sum of column two if the value in column one is the same?

How do I get a sum of column two if the value in column one is the same? The values below represent a segment of a much larger dataset

31128 166 31128 27 31128 0 31128 276 31128 0 31201 0 31201 2125 31201 0 31201 56 31201 0 31201 0 31201 0 31201 0 31235 2125 31235 13 31235 364 31235 1836 31235 379 31235 486

Answer 1

[Star Strider]

Use the unique and accumarray functions:

A = [31128  166
    31128  27
    31128  0
    31128  276
    31128  0
    31201  0
    31201  2125
    31201  0
    31201  56
    31201  0
    31201  0
    31201  0
    31201  0
    31235  2125
    31235  13
    31235  364
    31235  1836
    31235  379
    31235  486];

[A1u,ia,ic] = unique(A(:,1));
A2sum = accumarray(ic, A(:,2));
Result = [A1u  A2sum]

Result =
       31128         469
       31201        2181
       31235        5203

[Humblespud]

How would I get it that

Result = 
Result =
       31128            469
       31201           2130
       31235           5203

[Star Strider]

The code works by first getting the unique values in ‘A(:,1)’ and returns them in ‘A1u’. The ‘ic’ vector are the positions in ‘A(:,1)’ that correspond to each of them, so a 1 in ‘ic’ corresponds to an occurrence of ‘31128’, a 2 to ‘31201’, and so for the rest (since I assume there will be more).

The accumarray call uses the indices returned in ‘ic’ to accumulate (sum) the corrsponding values in ‘A(:,2)’, and returns that vector in ‘A2sum’. (See the documentation for accumarray for the details of all it can do.)

The ‘Result’ assignment concatenates ‘A1u’ and ‘A2sum’ to form a sort of table to make the output easier to interpret.