Predict for multiple models using linear algebra.

prediction_by_matrix_multiplication.R

library(purrr)

# two regressions
lm_fit <- lm(mpg ~ wt + cyl, data = mtcars)
bayes_fit <- rstanarm::stan_glm(mpg ~ wt + cyl, data = mtcars)

# design matrix [32 x 3]
X <- model.matrix(lm_fit)

# coefficient matrix [3 x 2]
B <- list(lm = lm_fit, bayes = bayes_fit) %>% 
  map_dfc(coef) %>% 
  as.matrix()

# predictions [32 x 2]
X %*% B