TF = ismember (A, B) returns a logical array TF of the same size as A containing true for each corresponding element of A that is in B and false otherwise. <undefined> elements are not equal with each other and always return false. If A and B are ordinal, they must have the same ordered set of categories. If neither A nor B are ordinal, then this restriction is relaxed and comparison is performed using the category names. Comparison between an ordinal and an unordered categorical array is not allowed. Either A or B may also be a string array, a character vector, or a cell array of character vectors containing one or multiple category names to compare against an unordered categorical array.

TF = ismember (A, B, 'rows') only applies to categorical matrices with the same number of columns, in which case the logical vector TF contains true for each row of A that is also a row in B. TF has the same number of rows as A.

[TF, index] = ismember (A, B) also returns an index array of the same size as A containing the lowest index in B for each element of A that is a member of B and 0 otherwise. If the 'rows' optional argument is used, then the returning index is a column vector with the same rows as A and it contains the lowest index in B for each row of A that is a member of B and 0 otherwise. If the 'legacy' optional argument is specified, then the highest index of matched elements is returned. Unless multiple matches exist, the 'legacy' option has no effect on the returned index.

Source Code: categorical