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rsyntaxformula

Adding extra variables to a formula

I want to add extra variables to a formula, with the use of a separate object part_B. As an example:

part_A <- as.formula("y ~ x1")
part_B <- c("x2", "x3")

I tried a couple of things, but one issue is that you cannot call as.formula on the object part_B (because in that case I could have created the formula by combining character vectors).

Desired Result

as.formula("y ~ x1 + x2 + x3")

Is there any way to do this? I guess one solution would be to create a function that writes the character vector as "y ~ x1 + x2 + x3" so it can be fed to as.formula.

Solution

  • Use reformulate and update like this:

    update(part_A, reformulate(c(".", part_B)))
## y ~ x1 + x2 + x3

    This also works:

    v <- all.vars(part_A)
reformulate(c(v[-1], part_B), v[1])
## y ~ x1 + x2 + x3