What is the meaning in this instrument

I want to know the meaning of this MATLAB command

>> v = unique(m(d==1,2))

where m and d are matrices with dimensions (50x2) and (50x1) respectively.

Answer 1

[Walter Roberson]

d == 1 where d is a vector, produces a logical vector as output -- a vector of true and false values.

When you use a logical vector as a subscript, that is called "logical indexing", and it selects for output all locations where the vector is true. In this context, those are used to select rows -- so the m(d==1,2) selects column 2 of all rows of m corresponding to the positions where d==1 is true.

v = unique(m(d==1,2))

acts the same as

temp = find(d==1);
v = unique(m(temp, 2))

[Alaaeldin Mohamed]

Thank you very much. It works well