In R, can I make the table() function return the number of NA values in a named element?

Question

I am using R to summarize a large amount of data for a report. I want to be able to use `lapply()` to generate a list of tables from the `table()` function, from which I can extract my desired statistics. There are a lot of these, so I've written a function to do it. My issue is that I am having difficulty returning the number of missing (`NA`) values even though I have that in each table, because I can't figure out how to tell R that I want the element from `table()` that holds the number of `NA` values. As far as I can tell, R is "naming" that element `NA`...and I can't call that. I'm trying to avoid writing some complex statement where I say something like `which(is.na(names(element[1]))) | names(element[1])=="var_I_want"` because I feel like that's just really wordy. I was hoping there was some way to either tell R to label the `NA` variable in each table with a character name, or to tell it to pick the one labeled `NA`, but I haven't had much luck yet. Minimal example: ``` exampl…

Accepted Answer

This is ugly (IMHO) but it works:

```
my_table <- function(x){
    setNames(table(x,useNA = "always"),c(sort(unique(x[!is.na(x)])),'NA'))
}
```

So you'd `lapply` this instead, and then you'd have access to the `NA` column.

Looking more closely, this is rooted in the behavior of `factor`:

```
levels(factor(c(1,NA,2),exclude = NULL))
[1] "1" "2" NA 
```

My recollection is that the distinction between a factor level of `NA` versus `"NA"` has been at the very least a source of confusion in R in the past. I feel like I've seen some debates about the merits of this on r-devel, but I can't recall for sure at the moment.

So the issue is, if you have a factor with `NA` values, what do you call the levels? Technically, this is correct, one of the levels is "missing" not literally "NA". It would be nice (IMHO) if `table` didn't adhere to this quite so strictly, though.

In R, can I make the table() function return the number of NA values in a named element?

Solution

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