Either i. a clustering or feature allocation distribution or ii. a
collection of clusterings or feature allocations. If x is a
B-by-n matrix, each of the B rows represents a
clustering of n items using cluster labels. For clustering
b, items i and j are in the same cluster if
x[b,i] == x[b,j]. If x is a list of length B, each
element of list represents a feature allocation using a binary matrix of
n rows and an arbitrary number of columns. For feature allocation
b, items i and j share m features if, for
k = 1, 2, ..., the expression x[[b]][i,k] == x[[b]][j,k] == 1
is true exactly m times.