Replacing explict strata arg

strata.R

library(RItools)
library(optmatch)
set.seed(20130801)
n <- 500

library(MASS)
xs <- mvrnorm(n,
              mu = c(1,2,3),
              Sigma = matrix(c(1, 0.5, 0.2,
                  0.5, 1, 0,
                  0.2, 0, 1), nrow = 3, byrow = T))

colnames(xs) <- paste0("x", 1:3)

p <- plogis(0.5 * xs[,1] - 0.25 * xs[,2] - 1)
z <- rbinom(n, p = p, size = 1)
s1 <- rep(c(0,1), each = n/2)
s2 <- rep(1:10, each = n/10)
ff <- fullmatch(match_on(glm(z ~ p, data = dat, family = binomial)), data = dat)

dat <- data.frame(z, xs, s1, s2, ff)

# should be equivalent to z ~ x1 + x2 + x3 + strata(s1) + strata(s2) + strata(ff)
# and no explict strata arg
res <- xBalance(z ~ x1 + x2 + x3,
                data = dat,
                report = 'all',
                strata = list("Unadj" = NULL,
                    "S1"   = ~ s1,
                    "S2"   = ~ s2,
                    "FF"   = ~ ff))