model_matrix() is a stricter version of stats::model.matrix(). Notably, model_matrix() will never drop rows, and the result will be a tibble.

model_matrix(terms, data)

Arguments

terms

A terms object to construct a model matrix with. This is typically the terms object returned from the corresponding call to model_frame().

data

A tibble to construct the design matrix with. This is typically the tibble returned from the corresponding call to model_frame().

Value

A tibble containing the design matrix.

Details

The following explains the rationale for some of the difference in arguments compared to stats::model.matrix():

  • contrasts.arg: Set the contrasts argument, options("contrasts") globally, or assign a contrast to the factor of interest directly using stats::contrasts(). See the examples section.

  • xlev: Not allowed because model.frame() is never called, so it is unnecessary.

  • ...: Not allowed because the default method of model.matrix() does not use it, and the lm method uses it to pass potential offsets and weights through, which are handled differently in hardhat.

Examples

# --------------------------------------------------------------------------- # Example usage framed <- model_frame(Sepal.Width ~ Species, iris) model_matrix(framed$terms, framed$data)
#> # A tibble: 150 x 3 #> `(Intercept)` Speciesversicolor Speciesvirginica #> <dbl> <dbl> <dbl> #> 1 1 0 0 #> 2 1 0 0 #> 3 1 0 0 #> 4 1 0 0 #> 5 1 0 0 #> 6 1 0 0 #> 7 1 0 0 #> 8 1 0 0 #> 9 1 0 0 #> 10 1 0 0 #> # … with 140 more rows
# --------------------------------------------------------------------------- # Missing values never result in dropped rows iris2 <- iris iris2$Species[1] <- NA framed2 <- model_frame(Sepal.Width ~ Species, iris2) model_matrix(framed2$terms, framed2$data)
#> # A tibble: 150 x 3 #> `(Intercept)` Speciesversicolor Speciesvirginica #> <dbl> <dbl> <dbl> #> 1 1 NA NA #> 2 1 0 0 #> 3 1 0 0 #> 4 1 0 0 #> 5 1 0 0 #> 6 1 0 0 #> 7 1 0 0 #> 8 1 0 0 #> 9 1 0 0 #> 10 1 0 0 #> # … with 140 more rows
# --------------------------------------------------------------------------- # Contrasts # Default contrasts y <- factor(c("a", "b")) x <- data.frame(y = y) framed <- model_frame(~y, x) # Setting contrasts directly y_with_contrast <- y contrasts(y_with_contrast) <- contr.sum(2) x2 <- data.frame(y = y_with_contrast) framed2 <- model_frame(~y, x2) # Compare! model_matrix(framed$terms, framed$data)
#> # A tibble: 2 x 2 #> `(Intercept)` yb #> <dbl> <dbl> #> 1 1 0 #> 2 1 1
model_matrix(framed2$terms, framed2$data)
#> # A tibble: 2 x 2 #> `(Intercept)` y1 #> <dbl> <dbl> #> 1 1 1 #> 2 1 -1
# Also, can set the contrasts globally global_override <- c(unordered = "contr.sum", ordered = "contr.poly") rlang::with_options( .expr = { model_matrix(framed$terms, framed$data) }, contrasts = global_override )
#> # A tibble: 2 x 2 #> `(Intercept)` y1 #> <dbl> <dbl> #> 1 1 1 #> 2 1 -1