Sum of a list of numbers if they're a certain value or not
23 views (last 30 days)
Show older comments
I have a list of numbers, and I'm trying to determine the sum of all of the numbers that have a value less than 55. I know that this will involve some sort of logic set-up, but I'm not familiar with how to set it up exactly. Any help is really appreciated.
0 Comments
Accepted Answer
bym
on 4 Dec 2011
Or even (without using sum)
x.'*(x<55)
[edit]
for x being a matrix
x = randi(100,20,20);
sx = x(:).'*(x(:)<55);
4 Comments
bym
on 5 Dec 2011
reading from left to right the line x(:).'*(x(:)<55);
x(:) returns all elements of x in a column (see doc colon)
.' transposes x(:)from column to row
* is matrix multiply
(x(:)<55) returns a column of 1's & 0's (1 is true x(n),55)
in summary, you are transforming the matrix in to 1 row and matrix multiplying it by a column of boolean values generated by the logical test. The addition is implicit in the matrix multiply
More Answers (2)
Walter Roberson
on 4 Dec 2011
Alternatives:
sum(x .* (x <= 55))
or
sum(x(find(x<=55)))
8 Comments
Image Analyst
on 5 Dec 2011
No, that's not it. It works just fine with <=. I just changed it to less than because that's what you said. But <= will also work fine - just try it. There must have been some other reason that you're not telling us and we don't know because you didn't share your code.
See Also
Categories
Find more on Matrix Indexing in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!