Incomplete sheet

This sheet is incomplete and could use some attention. Please submit code snippet suggestions as an issue or PR here.

formula

Create

Action	Code	Details
Intercept only	y ~ 1
With intercept and single variable	y ~ x
Without intercept, and single variable	y ~ -1 + x
With all variables	y ~ .
No response variable	~ 1
From string	as.formula(str)
From string	eval(parse(text='y ~ x'))	Not recommended

Test

Action	Code	Details
Is formula	is(f, 'formula')
Is formula or subclass	inherits(f, 'formula')
Formulas are equal	f1 == f2
Formulas are equal	isTRUE(all.equal(f1, f2))
Has response	attr(terms(f), 'response') != 0
Has intercept	attr(terms(f), 'intercept') != 0	Surely there is an easier way

Extract

Action	Code	Details
Variable names	all.vars(f)
Left-hand side variable names	all.vars(update(f, ~ 1))
Right-hand side variable names	all.vars(update(f, 1 ~ .))
Environment	environment(f)

Derive

Action	Code	Details
Add a term	update(f, ~ . + w)
Add terms	update(f, ~ . + w + z)
Set response	update(f, y ~ .)
Set terms	update(f, ~ w + z)
Remove response	update(f, NULL ~ .)
Remove response	formula(delete.response(terms(f)))
Remove intercept	update(f, ~ . + -1)
Remove environment	environment(f) = NULL	Useful for formula serialization to prevent the entire workspace from being serialized along with it

Evaluate

Action	Code	Details
Evaluate a formula with known coefficients	mm = model.matrix( ~ a + poly(b, 2, raw=TRUE), data.frame(a=1, b=2:4)) pred = coef %*% t(mm)

Convert

Action	Code	Details
String	deparse(f)
String array	as.character(f)