Applying Regex Across a Vector

Question

I'm at a loss why the following code doesn't work. The intention is to input a vector of strings, some of which can be converted to a number, some can't. The following 'sapply' function should use a regex to match numbers and then return the number or (if not) return the original.

sapply(c("test","6","-99.99","test2"), function(v){
  if(grepl("^[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?$",v)){as.numeric(v)} else {v}
})

Which returns the following result:

"test"      "6" "-99.99"  "test2" 

Edit: What I expect the code to return:

"test"      6  -99.99    "test2

I can run the if statement on each element successfully.

> if(grepl("^[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?$","test")){as.numeric("test")} else {"test"}
[1] "test"
if(grepl("^[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?$","6")){as.numeric("6")} else {"6"}
[1] 6

And etc...

I don't understand why this is happening. I guess I have two questions. One: Why is this happening? And two: Usually I'm pretty good at troubleshooting, but I have no idea where to even look for this. If you know the problem, how did you find/know the solution? Should I open up the internal lapply function code?

Answer 1

that happens because sapply returns a vector, and a vector can't be mixed. If you use lapply then you get a list result which can be mixed, the same code but with lapply instead of sapply works how you want it to.

Answer 2

@Jeremy points into right direction, you can use lapply, which returns a list. Or, you can tell sapply not to simplify result.

If simplification occurs, the output type is determined from the highest type of the return values in the hierarchy NULL < raw < logical < integer < double < complex < character < list < expression, after coercion of pairlists to lists.

out <- sapply(c("test","6","-99.99","test2"), function(v){

  if(grepl("^[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?$",v)){
    as.numeric(v)
  } else {
    v
  }
}, simplify = FALSE)
> out
$test
[1] "test"

$`6`
[1] 6

$`-99.99`
[1] -99.99

$test2
[1] "test2"