Error when creating R function that contains table()

Question

I'm trying to create a function that contains the table() function, but I keep returning the error "Error in table(df$var, df$arm) : all arguments must have the same length ". I've played around with every alternative option to referencing the columns that I can think of but to no avail.

Here is a reproduceable example:

x <- c(0, 1, 0, 1)
arm <- c("A", "A", "B", "B")
study.df <- data.frame(x, arm, row.names = NULL)


f.table <- function(df, var) {
  p <- table(df$var, df$arm) %>%
    fisher.test(alternative = "two.sided") %>%
    .$p.value
  return(p)
}

f.table(study.df, x)

probably a duplicate of https://stackoverflow.com/questions/12389318/dollar-sign-before-a-variable and https://stackoverflow.com/questions/18222286/dynamically-select-data-frame-columns-using-and-a-character-value — user20650, Aug 29 '21 at 21:01
Adding to @user20650's mention of dupes, this is also mixing non-standard evaluation (NSE) since you use `x` expecting the function to use `df$x`, which it will not do without deliberate effort. — r2evans, Aug 29 '21 at 21:11

score 2 · Accepted Answer · answered Aug 29 '21 at 21:00

2

As we are passing unquoted argument, use deparse/substitute and instead of $ use [[ for extraction

f.table <- function(df, var) {
   p <- table(df[[deparse(substitute(var))]], df$arm) %>%
     fisher.test(alternative = "two.sided") %>%
     .$p.value
   return(p)
 }

-testing

> f.table(study.df, x)
[1] 1

which is the same value we get outside the function

> table(study.df$x, study.df$arm) %>% fisher.test(alternative = "two.sided") %>%
+     .$p.value
[1] 1

answered Aug 29 '21 at 21:00

akrun

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1

Wow worked like a charm, thank you so much!! I never would have gotten there and I really appreciate your help. – wwa2199 Aug 29 '21 at 21:25

score 2 · Answer 2 · answered Aug 29 '21 at 21:01

You need to change how you call the argument var inside the function, here is a solution:

 f.table <- function(df, var) {
  p <-
    table(df[,var], df$arm) %>%
    fisher.test(alternative = "two.sided") %>%
    .$p.value
  return(p)
}

f.table(study.df, "x")

Error when creating R function that contains table()

2 Answers2