R: Generate Dummy Codes for a Factor

Dummy {DescTools}

R Documentation

Generate Dummy Codes for a Factor

Description

Generates a matrix of dummy codes (class indicators) for a given factor.

Usage

Dummy(x, method = c("treatment", "sum", "helmert", "poly", "full"),
      base = 1, levels = NULL)

Arguments

`x`	factor or vector of classes for cases.
`method`	defines the method of the contrasts being formed. Can be one out of `"treatment"`, `"sum"`, `"helmert"`, `"poly"`, `"full"`, whereas `"treatment"` is the default one. Abbreviations are accepted. The option `"full"` returns a full set of class indicators, say a dummy factor for EACH level of x. Note that this would be redundant for lm and friends!
`base`	an integer specifying which group is considered the baseline group.
`levels`	an optional vector of the values (as character strings) that `x` might have taken. The default is the unique set of values taken by as.character(x), sorted into increasing order of x. This is directly passed on to `factor`.

Value

a matrix with the dummy codes. The number of rows correspond to the number of elements in x and the number of columns to the number of its levels - 1, respectively to the number of levels given as argument -1.

When method full is chosen the number of columns will correspond to the number of levels.

Author(s)

Andri Signorell <andri@signorell.net>

References

Venables, W N and Ripley, B D (2002): Modern Applied Statistics with S. Fourth edition. Springer.

Examples

x <- c("red","blue","green","blue","green","red","red","blue")
Dummy(x)
Dummy(x, base = 2)

Dummy(x, method = "sum")


y <- c("Max","Max","Max","Max","Max","Bill","Bill","Bill")

Dummy(y)
Dummy(y, base = "Max")

Dummy(y, base = "Max", method="full")


# "Undummy" (revert the dummy coding)
m <- Dummy(y, method="full")
m
z <- apply(m, 1, function(x) colnames(m)[x==1])
z
identical(y, as.vector(z))

m <- Dummy(y)
m
z <- apply(m, 1, function(x) ifelse(sum(x)==0, attr(m,"base"), colnames(m)[x==1]))
z

[Package DescTools version 0.99.24 Index]