CODEWITHSUNDEEP
rmissing-data
marbel
marbel

Reputation: 7714

Convert NA into a factor level

I have a vector with NA values that I would like to replace by a new factor level NA.

a = as.factor(as.character(c(1, 1, 2, 2, 3, NA)))
a
[1] 1    1    2    2    3    <NA>
Levels: 1 2 3

This works, but it seems like a strange way to do it.

a = as.factor(ifelse(is.na(a), "NA", a))
class(a)
[1] "factor"

This is the expected output:

a
[1] 1  1  2  2  3  NA
Levels: 1 2 3 NA

Upvotes: 51

Views: 57887

Answers (3)

Rich Scriven
Rich Scriven

Reputation: 99321

You can use addNA().

x <- c(1, 1, 2, 2, 3, NA)
addNA(x)
# [1] 1    1    2    2    3    <NA>
# Levels: 1 2 3 <NA>

This is basically a convenience function for factoring with exclude = NULL. From help(factor) -

addNA modifies a factor by turning NA into an extra level (so that NA values are counted in tables, for instance).

So another reason this is nice is because if you already have a factor f, you can use addNA() to quickly add NA as a factor level without changing f. As mentioned in the documentation, this is handy for tables. It also reads nicely.

Upvotes: 70

LyzandeR
LyzandeR

Reputation: 37879

Set the exclude argument to NULL to include NAs as levels (and use factor instead of as.factor. Does the same thing and has more arguments to set):

a = factor(as.character(c(1, 1, 2, 2, 3, NA)), exclude = NULL)

> a
[1] 1    1    2    2    3    <NA>
Levels: 1 2 3 <NA>

Upvotes: 23

aosmith
aosmith

Reputation: 36076

You can add the NA as a level and change the level name to something more explicit than <NA> using fct_explicit_na from package forcats.

library(forcats)

By default you get the new level as (Missing):

fct_explicit_na(a)

[1] 1         1         2         2         3         (Missing)
Levels: 1 2 3 (Missing)

You can set it to something else:

fct_explicit_na(a, "unknown")

[1] 1       1       2       2       3       unknown
Levels: 1 2 3 unknown

Upvotes: 27

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