How can I take the values of one array, map the values as indices to another array, then generate a thrid array with the sum of former's elements??

I know the question is a bit confusing, so let me illustrate what i am trying to do with an example:

A = [ 2 1 4 2 3 2 4 0 ]

B = [ 1 1.5 2 1.5 2.5 3 1 ]

Now what I need is C = [ 1.5 5.5 2.5 3 ] Here is an explanation:

      A[2] = 1 ,                     so B[2] =             C[1]
      A[1], A[4], A[6] = 2,          so B[1]+B[4]+B[6]=    C[2]
      A[5] = 3                       so B[5] =             C[3]
      A[3], A[7] = 4                 so B[3]+B[5] =        C[4]

The index elements from A with common values (or a particular value) are mapped to B(same indices), then the elements with those indices in B are added (if one value, directly become elements in C) to get array C such that the values of A are indices of C.

Edited: A[8] = 0, so neglect that value.

Answer 1

[Greg Dionne]

You can use ACCUMARRAY. ACCUMARRAY is designed to take column vectors, not row vectors. So use this:

accumarray(A(:),B(:),[max(A) 1])'

Hope this helps!

-Greg

[Kirtiman]

I tried it and got this -

Error using accumarray First input SUBS must contain positive integer subscripts.

Error in Sysmodel (line 69) APload=accumarray(index(:), Userload(:), [max(index) 1])';

[Kirtiman]

Is it because index is a 1x93 double?

[Greg Dionne]

Probably because you have values in index(:) less than or equal to zero.

[Kirtiman]

Yes, index does have values equal to 0, what can be done to resolve this error?

[Image Analyst]

What do you want the value of C to be if the value in A is 0? There is no zeroeth column of B. Do you just want to add 1 to index (A) before you start?

[Kirtiman]

If the value in A is 0, then i don't want to consider it, i.e. i want that value to be neglected.

[Roger Stafford]

Then do this:

   t = A>0;
   C = accumarray(A(t),B(t),[max(A) 1])';

or even this:

   t = (A>0)&(A==round(A));
   C = accumarray(A(t),B(t),[max(A) 1])';

if A has negative or fractional values.

[Kirtiman]

Then what I get is this:

Error using accumarray Second input VAL must be a vector with one element for each row in SUBS, or a scalar.

Error in Sysmodel (line 69) APload=accumarray(index(t), Userload(t), [max(index) 1])';

[Roger Stafford]

Assuming A and B are still row vectors, try this:

   t = A>0;
   C = accumarray(A(t)',B(t)')';

[Kirtiman]

Thanks Greg and Roger. I removed elements containing zeros and then used method suggested by Greg.