taking data from a matrix and summing to a new vector

Im trying to take the values from a matrix, say 8 columns and 40 rows, and take column 3, 4, and 5s data and sum it up for every row and making a vertical vector of these values.

Answer 1

[Honglei Chen]

Here is an example

x = rand(40,8);
sum(x(:,[3 4 5]),2)