Problem
You want to rename the levels in a factor.
Solution
# A sample factor to work with.
x<-factor(c("alpha","beta","gamma","alpha","beta"))
x
#> [1] alpha beta gamma alpha beta
#> Levels: alpha beta gammalevels(x)
#> [1] "alpha""beta""gamma"
The easiest way is to use revalue() or mapvalues() from the plyr package:
library(plyr)
revalue(x, c("beta"="two", "gamma"="three"))
#> [1] alpha two three alpha two
#> Levels: alpha two threemapvalues(x, from = c("beta", "gamma"), to = c("two", "three"))
#> [1] alpha two three alpha two
#> Levels: alpha two three
If you don’t want to rely on plyr, you can do the following with R’s built-in functions.Note that these methods will modify x
directly; that is, you don’t have to save the result back into x.
# Renameby name: change"beta"to"two"
levels(x)[levels(x)=="beta"]<-"two"
# You can also renamebyposition, but this is a bit dangerous if your data
# can changein the future. If there is a changein the numberor positions of
# factor levels, then this can result in wrong data.
# Renamebyindexin levels list: change third item, "gamma", to"three".
levels(x)[3]<-"three"x
#> [1] alpha two three alpha two
#> Levels: alpha two three
# Renameall levelslevels(x)<-c("one","two","three")
x
#> [1] one two three one two
#> Levels: one two three
It’s possible to rename factor levels by name (without plyr), but keep in mind that this works only if ALL levels are present in the list; if any are not in the list, they will be replaced with NA.
# Rename all levels, by name
x<-factor(c("alpha","beta","gamma","alpha","beta"))
levels(x)<-list(A="alpha",B="beta",C="gamma")
x
#> [1] A B C A B#> Levels: A B C
It’s also possible to use R’s string search-and-replace functions to rename factor levels. Note that the ^ and $ surrounding alpha are there to ensure that the entire string matches. Without them, if there were a level named alphabet, it would also match, and the replacement would be onebet.
# A sample factor to work with.
x<-factor(c("alpha","beta","gamma","alpha","beta"))
x
#> [1] alpha beta gamma alpha beta
#> Levels: alpha beta gamma
levels(x)<-sub("^alpha$","one",levels(x))
x
#> [1] one beta gamma one beta
#> Levels: one beta gamma
# Across all columns, replace all instances of "a" with "X"
levels(x)<-gsub("a","X",levels(x))
x
#> [1] one betX gXmmX one betX
#> Levels: one betX gXmmX
# gsub() replaces all instances of the pattern in each factor level.
# sub() replaces only the first instance in each factor level.
See also