check a vector for duplicates and save as logical in matlab

You can use the unique function in MATLAB to identify the unique elements of a vector and the ismember function to determine which elements of the vector are duplicates. Here is an example code snippet:

main.m
vec = [1 2 3 2 4 5 4];
unique_vec = unique(vec);
is_duplicate = ismember(vec, unique_vec(2:end));
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In this code, unique(vec) returns [1 2 3 4 5], which corresponds to the unique elements of the original vector vec. The second line creates a logical vector is_duplicate indicating whether each element of vec is a duplicate (i.e., appears more than once) by comparing it against all but the first element of unique_vec.

Note that is_duplicate has the same size as vec and contains true for each duplicate element and false otherwise.