get_frex: Get FREX words
In dtburk/texanaaid: An Aide for Text Analysis

Get frequent and exclusive words for a group of documents, relative to other groups, based on a probability matrix of word occurrence.

1 2	get_frex(prob_mtrx, group_num, group_membership = NULL, wt = 0.5, values = FALSE)

`prob_mtrx`	A matrix with (named) columns for words, and rows for either documents or document groups. If each row represents a document, `group_membership` must be provided.
`group_num`	An integer corresponding to the document group of interest.
`group_membership`	An integer vector specifying the group membership of documents in `prob_mtrx`.
`wt`	A value between 0 and 1 specifying the weight to be given to word exclusivity in calculating FREX.
`values`	A logical specifying whether the function should return the actual FREX values or just words in decreasing FREX order.