use_contrasts function

Contrast code factors

Helper to do contrast coding. There are two options:

• Manually specify a matrix for code_by (implements use_contrast_matrix). Reference level is automatically set to the row that's always negative.
• Specify a style of contrast coding as a function. Label of the reference level should be specified in ...

use_contrasts(
  factor_col,
  code_by = NA,
  reference_level = NA,
  set_intercept = NA,
  drop_trends = NA,
  labels = NULL,
  as_is = FALSE,
  ...
)

Arguments

• factor_col: The factor column to use, eg data$gender
• code_by: Either a matrix or a function
• reference_level: The level to use as the reference level, default NA
• set_intercept: The intercept to use, default NA
• drop_trends: Whether to drop trends, default NA
• labels: Labels to use in the contrast matrix, must equal number of contrasts
• as_is: Logical, default FALSE, whether to suppress auto switching of the reference level to the first level if not specified
• ...: Additional arguments to be passed to use_contrast_function, specifically, which level you want the reference level to be

Returns

A contrast coding matrix with labels and proper reference level

Examples

# Create a contrast matrix given some factor vector with the specified
# reference level
use_contrasts(gl(5,2), sum_code, reference_level = 3)

# Set column labels; order for labels is the same as the column indices
use_contrasts(gl(3,2), scaled_sum_code, labels = c("2-1", "3-1"))

my_data <- mtcars
my_data$gear <- factor(mtcars$gear)

MASS::fractions(use_contrasts(my_data$gear, helmert_code))