R - Function that selects specific character in a column in data frame and replaces it

Question

I am trying to create a function in R that takes four arguments, namely: data frame, number, character 1 and character 2.

What I am trying to have as an output is this:

test_df <- data.frame(col1 = c("matt", "baby"), col2 = c("john", "luck"))

my_function(test_df, 1, "u", "o")

col1 col2
mutt john
buby luck

I was just wondering how should I specifically define the function to take the [number] column the user is entering? For the renaming, I guess the function rename() would be fine. Do I need to substitue with [x,x]?

Thank you!

Answer 1

If you have to create a function that takes a column as an argument you need to split out the data frame and column specification (using gsub() to do the actual replacement):

my_function <- function(df, column, pattern, replacement) {

  gsub(pattern, replacement, df[[column]])

}

Which would work like:

my_function(df = test_df, column = 1, pattern = "a", replacement = "u")
## [1] "mutt" "buby"

But, this has the downside that if you want to loop over multiple columns, for example with lapply() , the list specification becomes more complicated:

test_df[] <- lapply(colnames(test_df), my_function, df = test_df, pattern = "a", replacement = "u")
test_df
#   col1 col2
# 1 mutt john
# 2 buby luck

Which is much more complicated than:

test_df   <- data.frame(test_df, stringsAsFactors = FALSE)
test_df[] <- lapply(test_df, gsub, pattern = "a", replacement = "u")
test_df
#   col1 col2
# 1 mutt john
# 2 buby luck

(Note: ensure stringsAsFactors = FALSE for this to work. It's a good idea to use this as the default unless you explicitly want factors anyway)