Chapter 5 Data Specification

• formulas, model.frame, term objects, etc

• data / design matrix specification - recipes

habit: get the df right, then y ~ . in the formula. would be nice to still see the features in the call?

• ask users to use data.frames and tibbles, not matrices.

5.1 Formulas

5.1.1 Testing formulas

https://github.com/alexpghayes/formulize/blob/master/tests/testthat/test_formula.R

minimum set of formula tests (based on mtcars example dataset):

• using as.factor() inline mpg ~ as.factor(hp)
• using as.character() inline mpg ~ as.character(hp)
• intercept only mpg ~ 1
• no intercept mpg ~ disp + hp + drat - 1
• implicit intercept mpg ~ disp + hp + drat
• explicit intercept mpg ~ disp + hp + drat + 1
• polynomials with 1 term mpg ~ disp + hp + poly(drat, 1)
• polynomials with multiple terms mpg ~ disp + hp + poly(drat, 3)
• natural splines with 1 term mpg ~ disp + hp + ns(drat, 1)
• natural splines with multiple terms mpg ~ disp + hp + ns(drat, 3)
• explicit interactios mpg ~ drat + hp + drat:hp
• dot mpg ~ .
• star mpg ~ hp * drat
• as.is mpg ~ hp + I(drat^2)
• multiple response cbind
• multiple responses as matrix y ~ x where y is a matrix
• multiple predictors as matrix y ~ x where x is a matrix
• multiple predictos and responses together y ~ x, both x, y matrices
• transformed response log(mpg) ~ hp + drat

optional / to: - survival::Surv and survival::strata objects