Partitions of a set

How to calculate partitions of a finite set of positive integers of given length, like {1,2,...5} How to calculate partitions this set that has 4 partition sets. E.g.{1,2},{3},{4},{5}

[Walter Roberson]

Duplicates https://www.mathworks.com/matlabcentral/answers/479236-partitions-of-a-set