1

I need some help please. Let's say I have a matrix:

   4 5 6 6
a= 2 7 9 1
   9 0 4 5

I want to find the sum of row 2, without including the minimum value of row 2 (that's 1), I have tried this:

sum(a(2,:)~=1)

but it does not work. Can someone help?

2

Another way to do this without indexing is to subtract the minimum off of the sum,

sum(a(2, :)) - min(a(2, :))
0

Your code

sum(a(2,:)~=1)

tells you how many entries in the second row are not the minimum of 1. That's because the argument to sum,

>> a(2,:)~=1
ans = 
     1     1     1     0

is a logical array that indicates whether each of the numbers in that row is different from 1, and the logical values false and true are interpreted as numbers 0 and 1 by sum.

What you want to do is use these values for logical indexing into the row, and summing only the selected elements

ind = a(2,:)~=1;
sum(a(2,ind))

or shorter

sum(a(2,a(2,:)~=1))

Of course for generality it would be better to replace 1 by the expression min(a(2,:))

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.