CODEWITHSUNDEEP
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jdesilvio
jdesilvio

Reputation: 1854

R: Turn Input Variable to String - `deparse(substitute(x))` not working

I am trying to make a function that takes in a dataframe and adds a new variable which is the name of the input dataframe. For example:

foo <- data.frame(x = 1:10, y = rep(c("a", "b")))
mutate(foo, id = "foo")

This seemed relatively trivial to accomplish, since this works as it does here: 

var_as_string <- function(x) {deparse(substitute(x))}

var_as_string(foo)

Result:
[1] "foo"

I figured this would as well, but it doesn't:

add_id <- function(x) {
    mutate(x, id = deparse(substitute(x)))
}

add_id(foo)

Result:
   zz yy id
1   1  a  x
2   2  b  x
3   3  a  x
4   4  b  x
5   5  a  x
6   6  b  x
7   7  a  x
8   8  b  x
9   9  a  x
10 10  b  x

As a test, I tried this and it doesn't work as I thought it would either:

var_as_string2 <- function(x) {
  var_string <- var_as_string(x)
  var_string(x)
}

var_as_string2(foo)

Result:
[1] "x"

Is there a solution to this? Am I overlooking something here or do I have a fundamental misunderstanding of functions in R?

Upvotes: 4

Views: 1975

Answers (1)

konvas
konvas

Reputation: 14346

There is probably a better 1-line way of achieving this using lazyeval but this seems to work

add_id <- function(x) {
    s <- as.character(substitute(x))
    mutate(x, id = s)
}

add_id(foo)

(the idea compared to what you were trying to do is that you have to evaluate s outside the mutate call)

Upvotes: 3

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