Reorder factor levels by hand

This is a generalisaton of stats::relevel() that allows you to move any number of levels to any location.

fct_relevel(.f, ..., after = 0L)

Arguments

.f	A factor (or character vector).
...	Either a function (or formula), or character levels. A function will be called with the current levels, and the return value (which must be a character vector) will be used to relevel the function. Any levels not mentioned will be left in existing order, after the explicitly mentioned levels. Supports tidy dots.
after	Where should the new values be placed?

Examples

f <- factor(c("a", "b", "c", "d"), levels = c("b", "c", "d", "a"))
fct_relevel(f)
#> [1] a b c d
#> Levels: b c d a
fct_relevel(f, "a")
#> [1] a b c d
#> Levels: a b c d
fct_relevel(f, "b", "a")
#> [1] a b c d
#> Levels: b a c d

# Move to the third position
fct_relevel(f, "a", after = 2)
#> [1] a b c d
#> Levels: b c a d

# Relevel to the end
fct_relevel(f, "a", after = Inf)
#> [1] a b c d
#> Levels: b c d a
fct_relevel(f, "a", after = 3)
#> [1] a b c d
#> Levels: b c d a

# Revel with a function
fct_relevel(f, sort)
#> [1] a b c d
#> Levels: a b c d
fct_relevel(f, sample)
#> [1] a b c d
#> Levels: d a c b
fct_relevel(f, rev)
#> [1] a b c d
#> Levels: a d c b

# Using 'Inf' allows you to relevel to the end when the number
# of levels is unknown or variable (e.g. vectorised operations)
df  <- forcats::gss_cat[, c("rincome", "denom")]
lapply(df, levels)
#> $rincome
#>  [1] "No answer"      "Don't know"     "Refused"        "$25000 or more"
#>  [5] "$20000 - 24999" "$15000 - 19999" "$10000 - 14999" "$8000 to 9999" 
#>  [9] "$7000 to 7999"  "$6000 to 6999"  "$5000 to 5999"  "$4000 to 4999" 
#> [13] "$3000 to 3999"  "$1000 to 2999"  "Lt $1000"       "Not applicable"
#> 
#> $denom
#>  [1] "No answer"            "Don't know"           "No denomination"     
#>  [4] "Other"                "Episcopal"            "Presbyterian-dk wh"  
#>  [7] "Presbyterian, merged" "Other presbyterian"   "United pres ch in us"
#> [10] "Presbyterian c in us" "Lutheran-dk which"    "Evangelical luth"    
#> [13] "Other lutheran"       "Wi evan luth synod"   "Lutheran-mo synod"   
#> [16] "Luth ch in america"   "Am lutheran"          "Methodist-dk which"  
#> [19] "Other methodist"      "United methodist"     "Afr meth ep zion"    
#> [22] "Afr meth episcopal"   "Baptist-dk which"     "Other baptists"      
#> [25] "Southern baptist"     "Nat bapt conv usa"    "Nat bapt conv of am" 
#> [28] "Am bapt ch in usa"    "Am baptist asso"      "Not applicable"      
#> 

df2 <- lapply(df, fct_relevel, "Don't know", after = Inf)
lapply(df2, levels)
#> $rincome
#>  [1] "No answer"      "Refused"        "$25000 or more" "$20000 - 24999"
#>  [5] "$15000 - 19999" "$10000 - 14999" "$8000 to 9999"  "$7000 to 7999" 
#>  [9] "$6000 to 6999"  "$5000 to 5999"  "$4000 to 4999"  "$3000 to 3999" 
#> [13] "$1000 to 2999"  "Lt $1000"       "Not applicable" "Don't know"    
#> 
#> $denom
#>  [1] "No answer"            "No denomination"      "Other"               
#>  [4] "Episcopal"            "Presbyterian-dk wh"   "Presbyterian, merged"
#>  [7] "Other presbyterian"   "United pres ch in us" "Presbyterian c in us"
#> [10] "Lutheran-dk which"    "Evangelical luth"     "Other lutheran"      
#> [13] "Wi evan luth synod"   "Lutheran-mo synod"    "Luth ch in america"  
#> [16] "Am lutheran"          "Methodist-dk which"   "Other methodist"     
#> [19] "United methodist"     "Afr meth ep zion"     "Afr meth episcopal"  
#> [22] "Baptist-dk which"     "Other baptists"       "Southern baptist"    
#> [25] "Nat bapt conv usa"    "Nat bapt conv of am"  "Am bapt ch in usa"   
#> [28] "Am baptist asso"      "Not applicable"       "Don't know"          
#> 

# You'll get a warning if the levels don't exist
fct_relevel(f, "e")
#> Warning: Unknown levels in `f`: e
#> [1] a b c d
#> Levels: b c d a