[FEATURE] handle different number of teams in elo.run.multiteam

[BenoitLondon]

[EDIT] Actually it handles NA sorry please close... [EDIT]

Hi, currently when number of participants varies in each game, I have to pad the missing players with some artificial player "loser" with a very low initial rating to mimick the fact this fake player doesn't play and does not change the ratings of other players.

It could be possible to allow NA ( or use a special player name like "loser") and then remove the NA / loser in the 1v1 generated matchups

e.g. ( a quick way I think but it's probably easy to optimize further)

elo.run.multiteam2 <- function (formula, data, na.action, subset, k = NULL, initial.elos = NULL,
          ...)
{
    Call <- match.call()
    Call[[1L]] <- quote(elo::elo.model.frame)
    Call$required.vars <- c("elos", "k", "group", "regress")
    Call$ncol.k <- 2
    Call$ncol.elos <- 1
    mf <- eval(Call, parent.frame())
    if (nrow(mf) == 0)
        stop("No (non-missing) observations")
    Terms <- stats::terms(mf)
    if (any(mf$adjust.A != 0))
        warning("Any adjustments using 'adjust()' are being ignored.")
    mf2 <- elo:::multiteam_model_frame(mf)
    mf2 <- mf2[mf2$elo.B != "__loser__" & mf2$elo.A != "__loser__",]
    er <- elo.run(wins.A ~ elo.A + elo.B + k(k) + group(group) +
                      regress(regress, to = attr(mf$regress, "to"), by = attr(mf$regress,
                                                                              "by")), data = mf2,
                  initial.elos = initial.elos,...)
    er$Call <- Call
    er$terms <- Terms
    er$na.action <- stats::na.action(mf)
    er$n.matches <- nrow(mf)
    class(er) <- c("elo.run.multiteam", class(er))
    er
}

[BenoitLondon]

Oh actually I just realised it handles NA teams? ignore me :)