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Split and Unsplit Factors into Dummy Variables

Source: R/splitfactor.R
splitfactor.Rd

splitfactor() splits factor variables into dummy (0/1) variables. This can be useful when functions do not process factor variables well or require numeric matrices to operate. unsplitfactor() combines dummy variables into factor variables, undoing the operation of splitfactor().

Usage

splitfactor(
  data,
  var.name,
  drop.level = NULL,
  drop.first = TRUE,
  drop.singleton = FALSE,
  drop.na = TRUE,
  sep = "_",
  replace = TRUE,
  split.with = NULL,
  check = TRUE
)

unsplitfactor(
  data,
  var.name,
  dropped.level = NULL,
  dropped.na = TRUE,
  sep = "_",
  replace = TRUE
)

Arguments

data

A data.frame containing the variables to be split or unsplit. In splitfactor(), can be a factor variable to be split.

var.name

For splitfactor(), the names of the factor variables to split. If not specified, will split all factor variables in data. If data is a factor, the stem for each of the new variables to be created. For unsplitfactor(), the name of the previously split factor. If not specified and data is the output of a call to splitfactor(), all previously split variables will be unsplit.

drop.level

The name of a level of var.name for which to drop the dummy variable. Only works if there is only one variable to be split.

drop.first

Whether to drop the first dummy created for each factor. If "if2", will only drop the first category if the factor has exactly two levels. The default is to always drop the first dummy (TRUE).

drop.singleton

Whether to drop a factor variable if it only has one level.

drop.na

If NAs are present in the variable, how to handle them. If TRUE, no new dummy will be created for NA values, but all created dummies will have NA where the original variable was NA. If FALSE, NA will be treated like any other factor level, given its own column, and the other dummies will have a value of 0 where the original variable is NA.

sep

A character separating the the stem from the value of the variable for each dummy. For example, for "race_black", sep = "_".

replace

Whether to replace the original variable(s) with the new variable(s) (TRUE) or the append the newly created variable(s) to the end of the data set (FALSE).

split.with

A list of vectors or factors with lengths equal to the number of columns of data that are to be split in the same way data is. See Details.

check

Whether to make sure the variables specified in var.name are actually factor (or character) variables. If splitting non-factor (or non-character) variables into dummies, set check = FALSE. If check = FALSE and data is a data.frame, an argument to var.name must be specified.

dropped.level

The value of each original factor variable whose dummy was dropped when the variable was split. If left empty and a dummy was dropped, the resulting factor will have the value NA instead of the dropped value. There should be one entry per variable to unsplit. If no dummy was dropped for a variable, an entry is still required, but it will be ignored.

dropped.na

If TRUE, will assume that NAs in the variables to be unsplit correspond to NA in the unsplit factor (i.e., that drop.na = TRUE was specified in split.factor()). If FALSE, will assume there is a dummy called "var.name_stem_NA" (e.g., "x_NA") that contains 1s where the unsplit factor should be NA (i.e., that drop.na = FALSE was specified in split.factor(). If NAs are stored in a different column with the same stem, e.g., "x_miss", that name (e.g., "miss") can be entered instead.

Value

For splitfactor(), a data.frame containing the original data set with the newly created dummies. For unsplitfactor(). a data.frame containing the original data set with the newly created factor variables.

Details

If there are NAs in the variable to be split, the new variables created by splitfactor() will have NA where the original variable is NA.

When using unsplitfactor() on a data.frame that was generated with splitfactor(), the arguments dropped.na, and sep are unnecessary.

If split.with is supplied, the elements will be split in the same way data is. For example, if data contained a 4-level factor that was to be split, the entries of split.with at the same index as the factor and would be duplicated so that resulting entries will have the same length as the number of columns of data after being split. The resulting values are stored in the "split.with" attribute of the output object. See Examples.

See also

model.matrix()

Examples

data("lalonde", package = "cobalt")

lalonde.split <- splitfactor(lalonde, "race", 
                             replace = TRUE, 
                             drop.first = TRUE)
# A data set with "race_hispan" and "race_white" instead
# of "race".

lalonde.unsplit <- unsplitfactor(lalonde.split, "race", 
                                 replace = TRUE,
                                 dropped.level = "black")

all.equal(lalonde, lalonde.unsplit) #TRUE
#> [1] TRUE

# Demonstrating the use of split.with:
to.split <- list(letters[1:ncol(lalonde)],
                 1:ncol(lalonde))

lalonde.split <- splitfactor(lalonde, split.with = to.split,
                             drop.first = FALSE)
attr(lalonde.split, "split.with")
#> [[1]]
#>       treat         age        educ  race_black race_hispan  race_white 
#>         "a"         "b"         "c"         "d"         "d"         "d" 
#>     married    nodegree        re74        re75        re78 
#>         "e"         "f"         "g"         "h"         "i" 
#> 
#> [[2]]
#>       treat         age        educ  race_black race_hispan  race_white 
#>           1           2           3           4           4           4 
#>     married    nodegree        re74        re75        re78 
#>           5           6           7           8           9 
#>