misty (version 0.5.0)

dummy.c: Dummy Coding

Description

This function creates \(k - 1\) dummy coded 0/1 variables for a vector with k distinct values.

Usage

dummy.c(x, ref = NULL, names = "d", as.na = NULL, check = TRUE)

Value

Returns a matrix with k - 1 dummy coded 0/1 variables.

Arguments

x

a numeric vector with integer values, character vector or factor.

ref

a numeric value or character string indicating the reference group. By default, the last category is selected as reference group.

names

a character string or character vector indicating the names of the dummy variables. By default, variables are named "d" with the category compared to the reference category (e.g., "d1" and "d2"). Variable names can be specified using a character string (e.g., names = "dummy_" leads to dummy_1 and dummy_2) or a character vector matching the number of dummy coded variables (e.g. names = c("x.3_1", "x.3_2")) which is the number of unique categories minus one.

as.na

a numeric vector indicating user-defined missing values, i.e. these values are converted to NA before conducting the analysis.

check

logical: if TRUE, argument specification is checked.

Author

Takuya Yanagida

References

Rasch, D., Kubinger, K. D., & Yanagida, T. (2011). Statistics in psychology - Using R and SPSS. New York: John Wiley & Sons.

Examples

dat <- data.frame(x = c(1, 1, 1, 2, 2, 2, 3, 3, 3),
                  y = c("a", "a", "a", "b", "b", "b", "c", "c", "c"),
                  z = factor(c("B", "B", "B", "A", "A", "A", "C", "C", "C")),
                  stringsAsFactors = FALSE)

# Dummy coding of a numeric variable, reference = 3
dummy.c(dat$x)

# Dummy coding of a numeric variable, reference = 1
dummy.c(dat$x, ref = 1)

# Dummy coding of a numeric variable, reference = 3
# assign user-specified variable names
dummy.c(dat$x, names = c("x.3_1", "x.3_2"))

# Dummy coding of a numeric variable, reference = 3
# assign user-specified variable names and attach to the data frame
dat <- data.frame(dat, dummy.c(dat$x, names = c("x.3_1", "x.3_2")), stringsAsFactors = FALSE)

# Dummy coding of a character variable, reference = "c"
dummy.c(dat$y)

# Dummy coding of a character variable, reference = "a"
dummy.c(dat$y, ref = "a")

# Dummy coding of a numeric variable, reference = "c"
# assign user-specified variable names
dummy.c(dat$y, names = c("y.c_a", "y.c_b"))

# Dummy coding of a character variable, reference = "c"
# assign user-specified variable names and attach to the data frame
dat <- data.frame(dat, dummy.c(dat$y, names = c("y.c_a", "y.c_b")), stringsAsFactors = FALSE)

# Dummy coding of a factor, reference = "C"
dummy.c(dat$z)

# Dummy coding of a factor, reference = "A"
dummy.c(dat$z, ref = "A")

# Dummy coding of a numeric variable, reference = "C"
# assign user-specified variable names
dummy.c(dat$z, names = c("z.C_A", "z.C_B"))

# Dummy coding of a factor, reference = "C"
# assign user-specified variable names and attach to the data frame
dat <- data.frame(dat, dummy.c(dat$z, names = c("z.C_A", "z.C_B")), stringsAsFactors = FALSE)