Substitutes all factors in a data frame with the set of contrasts with which that factor is associated
expandFactors(data, ...)A data frame.
Additional arguments to be passed to model.matrix
A data frame.
The expandFactors function replaces all of the factors
in a data frame with the set of contrasts output by the contrasts
function or model.matrix. It may be useful for teaching purposes
when explaining relationship between ANOVA and regression.
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 factors using the default contrasts (usually 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 the contrasts using the contrasts.arg argument to model.matrix
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