Documentation of extract_subpopulations is not up-to-date

[cells2numbers]

The documentation of extract_subpopulations says

extract_subpopulations extracts the clusters enriched/de-enriched in a given set w.r.t a reference set. 

Actually, the cluster centers are calculated using data points from the reference and the population data frame.

[shntnu]

How is this?

@cells2numbers @mrohban

#' \code{extract_subpopulations} extracts clusters from population and reference sets 
#' and reports the frequency of points in each cluster for the sets

[cells2numbers]

That is actually what it is doing :)

[shntnu]

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