generate column values with multiple conditions in R

Question

I have a dataframe z and I want to create the new column based on the values of two old columns of z. Following is the process:

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Answer 1

Here's a version of an SQL decode in R for character vectors (untested with factors) that operates just like the SQL version. i.e. it takes an arbitrary number of target/replacement pairs, and optional last argument that acts as a default value (note that the default won't overwrite NAs).

I can see it being pretty useful in conjunction with dplyr's mutate operation.

> x <- c("apple","apple","orange","pear","pear",NA)

> decode(x, apple, banana)
[1] "banana" "banana" "orange" "pear"   "pear"   NA      

> decode(x, apple, banana, fruit)
[1] "banana" "banana" "fruit"  "fruit"  "fruit"  NA      

> decode(x, apple, banana, pear, passionfruit)
[1] "banana"       "banana"       "orange"       "passionfruit" "passionfruit" NA            

> decode(x, apple, banana, pear, passionfruit, fruit)
[1] "banana"       "banana"       "fruit"        "passionfruit" "passionfruit" NA  

Here's the code I'm using, with a gist I'll keep up to date here (link).

decode <- function(x, ...) {

  args <- as.character((eval(substitute(alist(...))))

  replacements <- args[1:length(args) %% 2 == 0]
  targets      <- args[1:length(args) %% 2 == 1][1:length(replacements)]

  if(length(args) %% 2 == 1)
    x[! x %in% targets & ! is.na(x)] <- tail(args,1)

  for(i in 1:length(targets))
    x <- ifelse(x == targets[i], replacements[i], x)

  return(x)

}