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Problem 640. Getting logical indexes

Created by Doug Hull

This is a basic MATLAB operation. It is for instructional purposes.


Logical indexing works like this.

thresh = 4;
vec    = [1 2 3 4 5 6 7 8];
vi     = (vec > thresh)
vi =
       0     0     0     0     1     1     1     1

Once you have this TRUE FALSE vector (I call it vi: Valid Indices)

It can be used to get the values out:

big = vec(vi)
big =
       5     6     7     8

Given a vector, vec, and a value, v, return a binary vector that represents the indices where vector, vec, is equal to scalar, v.

Note, this works just as well with scalars and matrices.


To get the indices where this comparison is true, see this Cody problem.

Problem Group

Solution Statistics

148 correct solutions 78 incorrect solutions
Last solution submitted on Oct 06, 2015