Interpret formulas in elo functions

A helper function to create the model.frame for many elo functions.

elo.model.frame(
  formula,
  data,
  na.action,
  subset,
  k = NULL,
  ...,
  required.vars = "elos",
  warn.k = TRUE,
  ncol.k = 1,
  ncol.elos = 2
)

Arguments

formula	A formula. See the help page for formulas for details.
data	A data.frame in which to look for objects in formula.
na.action	A function which indicates what should happen when the data contain NAs.
subset	An optional vector specifying a subset of observations.
k	A constant k-value (or a vector, where appropriate).
...	Other arguments (not in use at this time).
required.vars	One or more of c("wins", "elos", "k", "group", "regress"), denoting which variables are required to appear in the final model.frame.
warn.k	Should a warning be issued if k is specified as an argument and in formula?
ncol.k	How many columns (NCOL) should k have?
ncol.elos	How many Elo columns are expected?

See also

elo.run, elo.calc, elo.update, elo.prob