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Expand factors to a set of contrasts

Source: R/expandFactors.R
expandFactors.Rd

Replaces each factor variable in a data frame with its contrast-coded columns, leaving numeric variables unchanged.

Usage

expandFactors(data, ...)

Arguments

data

A data frame.

...

Additional arguments passed to model.matrix, such as contrasts.arg for specifying non-default contrast schemes.

Value

A data frame with factor columns replaced by numeric contrast columns.

Details

Each factor in data is replaced by the numeric contrast columns that model.matrix would generate for that factor (using treatment contrasts by default). Numeric variables pass through unchanged. This can be helpful when illustrating the connection between ANOVA and regression.

See also

model.matrix, contrasts

Examples

grading <- data.frame(
  teacher = factor(c("Amy", "Amy", "Ben", "Ben", "Cat")),
  gender  = factor(c("male", "female", "female", "male", "male")),
  grade   = c(75, 80, 45, 50, 65)
)

# expand using the default contrasts (treatment contrasts)
expandFactors(grading)
#>   teacherBen teacherCat gendermale grade
#> 1          0          0          1    75
#> 2          0          0          0    80
#> 3          1          0          0    45
#> 4          1          0          1    50
#> 5          0          1          1    65

# specify different contrasts via contrasts.arg
my.contrasts <- list(teacher = "contr.helmert", gender = "contr.treatment")
expandFactors(grading, contrasts.arg = my.contrasts)
#>   teacher1 teacher2 gendermale grade
#> 1       -1       -1          1    75
#> 2       -1       -1          0    80
#> 3        1       -1          0    45
#> 4        1       -1          1    50
#> 5        0        2          1    65