SUM of selected elements in Matrix

i have matrix

M = [1 1 2 60;

2 3 2 90;

3 1 3 240;

4 2 3 200;

5 3 3 160]

i want to select 1 from 2nd column and acoording to that i want to SUM of 60 and 240. same way i want to select 3 from 2nd column and SUM of 90 and 160.

how to creat?

Answer 1

[Ameer Hamza]

Are you looking for something like this

M = [1  1  2   60;
    2  3  2   90;
    3  1  3  240;
    4  2  3 200;
    5  3  3 160];

result = splitapply(@sum, M(:,4), M(:,2))

Result

>> result
result =
   300
   200
   250

[ANAND ASP]

yes exactly, thank you so much...

could you pass formula for subtraction

i want to select 2 from 2nd column and 3rd column and i want

sum like : + 200

- 60

- 90

= 50

[Ameer Hamza]

In that case, you can just use logical indexing

M = [1  1  2   60;
    2  3  2   90;
    3  1  3  240;
    4  2  3 200;
    5  3  3 160];

idx1 = M(:,2)==2;
idx2 = M(:,3)==2;

result = sum(M(idx1,4))-sum(M(idx2,4))