Why is the result of my logical indexing smaller than the original vector?

I have a vector "x" and a logical indexing vector "idx", which is the same size as "x". However, when I index into "x" using "idx", the result is a different size.

Why does this happen?

Answer 1

[MathWorks Support Team]

Logical indexing in MATLAB only returns values for the locations where indexing vector is 1, any other values from the original vector are ignored.

To acquire a result of the same size of "x" and "idx", you can consider using the "element-wise multiplication" operator ( .* ), or the "logical and" operator ( & ). For more information, please refer to the following documentation page on Matrix Indexing:

https://www.mathworks.com/help/matlab/math/matrix-indexing.html#bq7egb6-1