Internal formula term manipulation functions
These are helper function used in the formula interface of
varComp.test. They either sort or split the formula terms involving ":".
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A list converted from a call.
A character scalar of a formula term to be re-ordered alphanumerically with respect to the components separated by ":".
A character vector whose elements have higher priority to be ordered to the front of the term.
The main use of
sortTerm is to transform an interaction term like "B:A" into ordered form "A:B" such that redundant terms are easier to be identified. The results will depend on the system locale.
callList2terms returns a character vector of individual terms (possibly with duplicates).
splitTerm returns a character vector of unique individual components in the
sortTerm returns a character scalar with individual components sorted.
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