Convert a formula to a named character vector in analogy tasks.
analogy(formula)a formula object that defines the relationship between words
using + or - operators.
a named character vector to be passed to similarity().
analogy(~ berlin - germany + france)
#> berlin germany france
#> 1 -1 1
analogy(~ quick - quickly + slowly)
#> quick quickly slowly
#> 1 -1 1