A helper class for list of terms in an formula

Typically generated by list_rhs.formula(), it contains, in addition to a list of call() or similar objects, attributes "sign" and "env", containing, respectively a vector of signs that the terms had in the original formula and a list of environments of the formula from which the term has been extracted. Indexing and concatenation methods preserve these.

term_list(x, sign = +1, env = NULL)

as.term_list(x, ...)

# S3 method for class 'term_list'
as.term_list(x, ...)

# Default S3 method
as.term_list(x, sign = +1, env = NULL, ...)

# S3 method for class 'term_list'
c(x, ...)

# S3 method for class 'term_list'
x[i, ...]

# S3 method for class 'term_list'
print(x, ...)

Arguments

x

a list of terms or a term; a term_list

sign

a vector specifying the signs associated with each term (-1 and +1)

env

a list specifying the environments, or NULL

...

additional arguments to methods

i

list index

See also

list_rhs.formula(), list_summands.call()

Examples

e1 <- new.env()
f1 <- a~b+c
environment(f1) <- e1
f2 <- ~-NULL+1

(l1 <- list_rhs.formula(f1))
#> Term List:
#> + b <environment: 0x558aa0731e78>
#> + c <environment: 0x558aa0731e78>
(l2 <- list_rhs.formula(f2))
#> Term List:
#> - NULL <environment: 0x558aa071e5b0>
#> + 1 <environment: 0x558aa071e5b0>

(l <- c(l1,l2))
#> Term List:
#> + b <environment: 0x558aa0731e78>
#> + c <environment: 0x558aa0731e78>
#> - NULL <environment: 0x558aa071e5b0>
#> + 1 <environment: 0x558aa071e5b0>
#> Error: identical(attr(l, "env"), rep(list(e1, globalenv()), each = 2)) is not TRUE

(l <- c(l2[1], l1[2], l1[1], l1[1], l2[2]))
#> Term List:
#> - NULL <environment: 0x558aa071e5b0>
#> + c <environment: 0x558aa0731e78>
#> + b <environment: 0x558aa0731e78>
#> + b <environment: 0x558aa0731e78>
#> + 1 <environment: 0x558aa071e5b0>
#> Error: identical(attr(l, "env"), list(globalenv(), e1, e1, e1, globalenv())) is not TRUE