spatstat.utils (version 1.13-0)

termsinformula: Manipulate Formulae

Description

Operations for manipulating formulae.

Usage

termsinformula(x)
variablesinformula(x)
offsetsinformula(x)
lhs.of.formula(x)
rhs.of.formula(x, tilde=TRUE)
lhs.of.formula(x) <- value
rhs.of.formula(x) <- value
can.be.formula(x)
identical.formulae(x,y)

Arguments

x,y

Formulae, or character strings representing formulae.

tilde

Logical value indicating whether to retain the tilde.

value

Symbol or expression in the R language. See Examples.

Value

variablesinformula, termsinformula and offsetsinformula return a character vector.

rhs.of.formula returns a formula. lhs.of.formula returns a symbol or language object, or NULL.

can.be.formula and identical.formulae return a logical value.

Details

variablesinformula(x) returns a character vector of the names of all variables which appear in the formula x.

termsinformula(x) returns a character vector of all terms in the formula x (after expansion of interaction terms).

offsetsinformula(x) returns a character vector of all offset terms in the formula.

rhs.of.formula(x) returns the right-hand side of the formula as another formula (that is, it removes the left-hand side) provided tilde=TRUE (the default). If tilde=FALSE, then the right-hand side is returned as a language object.

lhs.of.formula(x) returns the left-hand side of the formula as a symbol or language object, or NULL if the formula has no left-hand side.

lhs.of.formula(x) <- value and rhs.of.formula(x) <- value change the formula x by replacing the left or right hand side of the formula by value.

can.be.formula(x) returns TRUE if x is a formula or a character string that can be parsed as a formula, and returns FALSE otherwise.

identical.formulae(x,y) returns TRUE if x and y are identical formulae (ignoring their environments).

Examples

# NOT RUN {
  f <- (y ~ x + z*w + offset(h))
  lhs.of.formula(f)
  rhs.of.formula(f)
  variablesinformula(f)  
  termsinformula(f)
  offsetsinformula(f)
  g <- f
  environment(g) <- new.env()
  identical(f,g)
  identical.formulae(f,g)
  lhs.of.formula(f) <- quote(mork) # or as.name("mork")
  f
  rhs.of.formula(f) <- quote(x+y+z) # or parse(text="x+y+z")[[1]]
  f
# }