Example of using divide.R with Zelig

divide-Zelig-example.R

library(Zelig)

# Divide a Data Frame or Matrix Into Subsets
# @param obj a data.frame or matrix to be split into subsets, divided by the
# categorical variable
# @param by a character-string, specifying the column to subset
# @return a list, containing the subsetted data sets. The names of the list
# correspond to the value of the subsetted list
divide <- function (obj, by) {
  # Get the set of possible values
  column.levels <-if (is.factor(obj[, by])) {
    levels(obj[, by])
  } else {
    unique(obj[, by])
  }
  # A list used to store each individual data.frame
  res <- list()
  # Iterate through all possible values and store each subset in a separate
  # entry in the list
  for (val in column.levels) {
    # Determine which rows match this value
    hits <- obj[, by] == val
    # Store data set temporarily in a local value
    data.set <- obj[hits, ]
    # Assign levels to the column. This adds levels to string data.
    levels(data.set[, by]) <- column.levels
    # Store data set in list
    res[[val]] <- data.set
  }

  # Return list
  res
}

data(turnout)

d <- divide(turnout, by = "race")

z <- zelig(vote ~ educate, model = "logit", data=d)
x <- setx(z)
s <- sim(z, x)

summary(s)

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