Cleaning Up Factor Levels (Collapsing Multiple Levels/Labels)

Cleaning up factor levels (collapsing multiple levels/labels)

UPDATE 2: See Uwe's answer which shows the new "tidyverse" way of doing this, which is quickly becoming the standard.

UPDATE 1: Duplicated labels (but not levels!) are now indeed allowed (per my comment above); see Tim's answer.

ORIGINAL ANSWER, BUT STILL USEFUL AND OF INTEREST:
There is a little known option to pass a named list to the levels function, for exactly this purpose. The names of the list should be the desired names of the levels and the elements should be the current names that should be renamed. Some (including the OP, see Ricardo's comment to Tim's answer) prefer this for ease of reading.

x <- c("Y", "Y", "Yes", "N", "No", "H", NA)
x <- factor(x)
levels(x) <- list("Yes"=c("Y", "Yes"), "No"=c("N", "No"))
x
## [1] Yes  Yes  Yes  No   No   <NA>  <NA>
## Levels: Yes No

As mentioned in the levels documentation; also see the examples there.

value: For the 'factor' method, a
vector of character strings with length at least the number
of levels of 'x', or a named list specifying how to rename
the levels.

This can also be done in one line, as Marek does here: https://stackoverflow.com/a/10432263/210673; the levels<- sorcery is explained here https://stackoverflow.com/a/10491881/210673.

> `levels<-`(factor(x), list(Yes=c("Y", "Yes"), No=c("N", "No")))
[1] Yes  Yes  Yes  No   No   <NA>
Levels: Yes No

Collapsing multiple factor levels of (messy) character variable in R

A friend of mine actually provided the answer. It's nothing to do with the data structure.

This does the job:

dt$x <- fct_collapse(dt$x, 
                          No = c(
                            "I don't allow anything", 
                             "..."),
                          Yes= c(
                             "Number of visitors ,annual sales, sales growth",
                             "number of customers", 
                             "Net sales", 
                             "..."),
                          Maybe= c(
                              "The CEO's approval is needed.", 
                              "To be discussed")
                               )

I still don't know why the first option I posted above doesn't work though (it did perfectly well with another variable).

Problem collapsing levels of a factor in R

Have you tried making Nationality a factor first?

df <- data.frame(ID=seq(1:10),
                 Nationality=c("espanol", "spaniol", "ESPANOL",
                               "spanish", "colombia", "Colombian",
                               "British", "brit", "ESPanol", "UK")
)
library(forcats) 


df2 <- df %>% 
  mutate(Nationality = factor(Nationality)) %>% 
 mutate(Nationality = fct_collapse(Nationality, Spanish = c("espanol", "spaniol", "ESPANOL", "spanish", "ESPanol"),
                                       Colombian = c("colombia", "Colombian"),
                                       British = c("British", "brit", "UK")))



#more concise

mutate(across(Nationality, ~ fct_collapse(factor(.), 
Spanish = c("espanol", "spaniol", "ESPANOL", "spanish", "ESPanol"), 
Colombian = c("colombia", "Colombian"), 
British = c("British", "brit", "UK")
))) 

Only certain values of column as levels in factor

Yes. Use the labels option:

x <- c("a","a","b","b","happy", "sad", "angry")
levels = c("a", "b", "happy", "sad", "angry")
labels = c("letter", "letter", "happy", "sad", "angry")

y <- factor(x, levels, labels = labels)

y

https://rdrr.io/r/base/factor.html

"Duplicated values in labels can be used to map different values of x to the same factor level."

EDIT: Your mistake in the above code example is the nested vector.

Combine factor levels

Just do

 levels(data2)[2:3] <- '(1,4]'
 data2
 #[1] (0,1] (1,4] (0,1] (0,1] (1,4] (1,4] (1,4] (1,4] (1,4] (1,4] (1,4] (1,4]
#[13] (1,4]
#Levels: (0,1] (1,4]

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