CODEWITHSUNDEEP
rregression
mat
mat

Reputation: 2617

R: Dynamically update formula

How can I dynamically update a formula?

Example:

myvar <- "x"

update(y ~ 1 + x, ~ . -x)
# y ~ 1 (works as intended)

update(y ~ 1 + x, ~ . -myvar)
# y ~ x (doesn't work as intended)

update(y ~ 1 + x, ~ . -eval(myvar))
# y ~ x (doesn't work as intended)

Upvotes: 5

Views: 417

Answers (1)

jay.sf
jay.sf

Reputation: 72813

You can use paste() within the update()call.

myvar <- "x"
update(y ~ 1 + x, paste(" ~ . -", myvar))
# y ~ 1

Edit

As @A.Fischer noted in the comments, this won't work if myvar is a vector of length > 1

myvar <- c("k", "l")
update(y ~ 1 + k + l + m, paste(" ~ . -", myvar))
# y ~ l + m
# Warning message:
# Using formula(x) is deprecated when x is a character vector of length > 1.
#   Consider formula(paste(x, collapse = " ")) instead.

Just "k" gets removed, but "l" remains in the formula.

In this case we could transform the formula into a strings, add/remove what we want to change and rebuild the formula using reformulate, something like:

FUN <- function(fo, x, negate=FALSE) {
  foc <- as.character(fo)
  s <- el(strsplit(foc[3], " + ", fixed=T))
  if (negate) {
    reformulate(s[!s %in% x], foc[2], env=.GlobalEnv)
  } else {
    reformulate(c(s, x), foc[2], env=.GlobalEnv)
  }
}

fo <- y ~ 1 + k + l + m

FUN(fo, c("n", "o"))  ## add variables
# y ~ 1 + k + l + m + n + o
FUN(fo, c("k", "l"), negate=TRUE))  ## remove variables
# y ~ 1 + m

Upvotes: 5

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