Converts two or more factors into a new factor whose value is 0 where the original factors are not all equal, and nonzero otherwise.
One or more factors
Used mainly in regression models for data classified by
two or more factors with the same levels. By default,
operates on k-level factors to produce a new factor having k+1 levels;
binary = TRUE is specified, the result is a coarser binary
variable equal to 1 where all of the input factors are equal and 0
Either a factor (if
binary = FALSE) or a 0-1 numeric vector
binary = TRUE).
David Firth and Heather Turner
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