I have created a custom function to replace values with NA to understand how functions work in R:

replacewithna <- function(x) {
  if(x == -99) {
    return(NA)
  }
  else {
    return(x)
  }
}

I have a dataframe with several columns and values which contain "-99" in certain elements and want to apply the custom function I created to each element. I have been able to do this with a for loop:

for (i in 1:nrow(survey2)) {
  for (j in 1:ncol(survey2)) {
    survey2[i,j] <- replacewithna2(survey2[i,j], NA)
  }
}

However, I can’t do the same with a lapply. How can I use my replace function with a function from the apply family like so:

survey1 <- lapply(survey1, replacewithna)

Currently I have the following error: "Error in if (x == -99) { : the condition has length > 1"

>Solution :

Try a vectorized version of your function with ifelse or, like below, with is.na<-.

replacewithna <- function(x) {
  is.na(x) <- x == -99
  x
}

With ifelse it is a one-liner:

replacewithna <- function(x) ifelse(x == -99, NA, x)

Note

With both functions, if survey1 or survey2 are data.frames, the correct way of lapplying the function and keep the dimensions, the tabular format, is

survey1[] <- lapply(survey1, replacewithna)

The square parenthesis are very important.