R: Replacing NAs in all factors with 'Missing'

With a simple combination of mutate_if and fct_explicit_na, you can replace all NAs in all factors with “Missing”:

	library(dplyr) # gives mutate_if
	library(forcats) # gives fct_explicit_na

	#example dataframe, a and c are factors,
	#b is numeric, d is boolean (TRUE/FALSE)
	mydata = data.frame(
	a = c( 'Yes', 'No', NA),
	b = c( 0.5, NA, 0.6),
	c = c( 'No', NA, 'Yes'),
	d = c( TRUE, NA, FALSE)
	)

	# Making the missing fields in the columns which are factors explicit
	#(by default, fct_explicit_na changes NAs "(Missing)"):
	newdata1 = mydata %>%
	mutate_if(is.factor, fct_explicit_na)

	# changing the missing label to "Dunno"
	#(note how the syntax is a little bit different
	# than when using fct_explicit_na on a single column)
	newdata2 = mydata %>%
	mutate_if(is.factor, fct_explicit_na, na_level = 'Dunno')


	# on a single column it would look like:
	mydata$a %>% fct_explicit_na(na_level = 'Dunno')

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