Get and Set Treatment Contrasts for Independent Variables in Data

get_contr_data() shows the "contrasts" attributes of all or selected factors within a data frame.

set_contr_treat() sets the "contrasts" attribute for selected factors within a data frame to a treatment contrast matrix with individually specified baseline levels.

set_contr_treat()<- is the replacement function form.

Usage

get_contr_data(data, ...)

set_contr_treat(data, ..., .baseline = NULL, .verbose = TRUE)

set_contr_treat(data, ..., .verbose = FALSE) <- value

Arguments

data: a data frame, or a data frame extension (e.g. a tibble).
...: <tidy-select> The selection of one or more factors in data for getting or setting contrasts.
.baseline: a numeric vector of length equal to the number of contrasts to be set specifying which level is considered the baseline.
.verbose: logical, whether to print "before and after" contrast matrices for factors in data.
value: numeric, see .baseline argument.

Value

The original dataframe or tibble with the "contrasts" attributes set for selected factors.

Details

get_contr_data() returns the "contrasts" attributes of all or selected factors.

Factors in .data may be selected for getting and setting contrasts using the ... argument with the <tidy-select> syntax of package dplyr, including use of selection helpers. If no ... arguments are supplied, all categorical variables in data (i.e., character or factor columns) will be selected.

The "contrasts" attribute of factors selected with ... are set using the contrast function contr.treatment with baseline factor levels as specified numerically in the argument .baseline or the value argument in the case of the replacement function form set_contrasts()<-. If no .baseline argument is supplied, by default the first factor level is used as baseline.

The individual .baseline (or .value) argument values are capped to be no greater than nlevels for each of the corresponding factors selected in .... Hence, to ensure the last level is the reference level, a baseline value can be specified as a large integer (e.g., 99L), which may be convenient when using set_contr_treat() programmatically.

Examples