what dos this instruction mean

i meet this instruction when analyzing a matlab file could you help me what does it mean ?

yone=(y==i)+(y~=i)*-1;

when y is a column vector and i is fix number i=4;

what will be the size of yone in this case ?

Answer 1

[Walter Roberson]

A value of "1" where the entries are "i", and a value of "-1" where the entries are not "i", and 0 where the entries are NaN.

[Jan]

Equivalent:

yone = 2 * (y==i) - 1;