Extract parents from the ancestor sets

Faithful port of rcd.py's extract_parents() (original 318-343 lines).

Usage

extract_parents(X, M, cor_alpha)

Arguments

X

(uncentered) data matrix

M

ancestor-set list from extract_ancestors()

cor_alpha

correlation-test significance level

Value

list of length ncol(X); each element is a sorted integer vector of parent indices (subset of the corresponding ancestor set)