replace <NA> with NA - r

Question

I have a data frame containing entries; It appears that these values are not treated as NA since is.na returns FALSE. I would like to convert these values to NA but could not find the way.

Answer 1

Use dfr[dfr=="<NA>"]=NA where dfr is your dataframe.
For example:
> dfr<-data.frame(A=c(1,2,"<NA>",3),B=c("a","b","c","d"))
> dfr
A B
1 1 a
2 2 b
3 <NA> c
4 3 d
> is.na(dfr)
A B
[1,] FALSE FALSE
[2,] FALSE FALSE
[3,] FALSE FALSE
[4,] FALSE FALSE
> dfr[dfr=="<NA>"] = NA **key step**
> is.na(dfr)
A B
[1,] FALSE FALSE
[2,] FALSE FALSE
[3,] TRUE FALSE
[4,] FALSE FALSE

Answer 2

The two classes where this is likely to be an issue are character and factor. This should loop over a dtaframe and convert the "NA" values into true <NA>'s but just for those two classes:
make.true.NA <- function(x) if(is.character(x)||is.factor(x)){
is.na(x) <- x=="NA"; x} else {
x}
df[] <- lapply(df, make.true.NA)
(Untested in the absence of a data example.) The use of the form: df_name[] will attempt to retain the structure of the original dataframe which would otherwise lose its class attribute. I see that ujjwal thinks your spelling of NA has flanking "<>" characters so you might try this functions as more general:
make.true.NA <- function(x) if(is.character(x)||is.factor(x)){
is.na(x) <- x %in% c("NA", "<NA>"); x} else {
x}

Answer 3

You can do this with the naniar package as well, using replace_with_na and associated functions.
dfr <- data.frame(A = c(1, 2, "<NA>", 3), B = c("a", "b", "c", "d"))
library(naniar)
# dev version - devtools::install_github('njtierney/naniar')
is.na(dfr)
#> A B
#> [1,] FALSE FALSE
#> [2,] FALSE FALSE
#> [3,] FALSE FALSE
#> [4,] FALSE FALSE
dfr %>% replace_with_na(replace = list(A = "<NA>")) %>% is.na()
#> A B
#> [1,] FALSE FALSE
#> [2,] FALSE FALSE
#> [3,] TRUE FALSE
#> [4,] FALSE FALSE
# You can also specify how to do this for many variables
dfr %>% replace_with_na_all(~.x == "<NA>")
#> # A tibble: 4 x 2
#> A B
#> <int> <int>
#> 1 2 1
#> 2 3 2
#> 3 NA 3
#> 4 4 4
You can read more about using replace_with_na here