Remove unused levels

This function removes unused levels of a factor or in a data.frame. See examples.

rm.unused.levels(x, v = NULL)

Arguments

x

a factor or a data frame

v

a list of variables (optional, if x is a data frame)

Details

If x is a data frame, only factor variables of x will be impacted. If a list of variables is provided through v, only the unused levels of the specified variables will be removed.

Author

Joseph Larmarange <joseph@larmarange.net>

Examples

df <- data.frame(v1 = c("a", "b", "a", "b"), v2 = c("x", "x", "y", "y"))
df$v1 <- factor(df$v1, c("a", "b", "c"))
df$v2 <- factor(df$v2, c("x", "y", "z"))
df
#>   v1 v2
#> 1  a  x
#> 2  b  x
#> 3  a  y
#> 4  b  y
str(df)
#> 'data.frame':	4 obs. of  2 variables:
#>  $ v1: Factor w/ 3 levels "a","b","c": 1 2 1 2
#>  $ v2: Factor w/ 3 levels "x","y","z": 1 1 2 2
str(rm.unused.levels(df))
#> 'data.frame':	4 obs. of  2 variables:
#>  $ v1: Factor w/ 2 levels "a","b": 1 2 1 2
#>  $ v2: Factor w/ 2 levels "x","y": 1 1 2 2
str(rm.unused.levels(df, "v1"))
#> 'data.frame':	4 obs. of  2 variables:
#>  $ v1: Factor w/ 2 levels "a","b": 1 2 1 2
#>  $ v2: Factor w/ 3 levels "x","y","z": 1 1 2 2