Multiplying values in one column with values in another, depending on criteria

Hi Everyone,

Suppose I have the following matrix:

A =

1.0__0.7__4.4__0.9__50.9

3.0__0.8__5.2__1.0__28.7

6.0__0.5__3.2__0.7__10.5

7.0__-0.5__3.6__0.8__87.7

Now I wish to calculate a value, which is found as follows:

1. Multiply the values in column 2, with the corresponding values in column 5, where the corresponding value in column 4 is greater than or equal to 0.8.

2. Sum the values found in step 1.

So, the answer I am looking for is:

0.7*50.9 + 0.8*28.7 + -0.5*87.7 = 14.74

What expression might do this?

Regards,

Ulrik

Answer 1

[Teja Muppirala]

One way to do it:

sum( A(:,2) .* A(:,5) .* (A(:,4) >= 0.8) )

[Teja Muppirala]

Another possibility,

idx = A(:,4) >= 0.8;

sum( A(idx,2) .* A(idx,5) )

[Ulrik Nash]

Thank you very much for the swift reply, Teja!