Replace contents of factor column in R dataframe

Question

I need to replace the levels of a factor column in a dataframe  Using the iris dataset as an example  how would I replace any cells which contain virginica with setosa in the Species column   I expected the following to work  but it generates a warning message and simply inserts NAs   iris Species iris Species     virginica    lt -  setosa

User · Accepted Answer

I bet the problem is when you are trying to replace values with a new one, one that is not currently part of the existing factor's levels:

levels(iris$Species)
# [1] "setosa"     "versicolor" "virginica"

Your example was bad, this works:

iris$Species[iris$Species == 'virginica'] <- 'setosa'

This is what more likely creates the problem you were seeing with your own data:

iris$Species[iris$Species == 'virginica'] <- 'new.species'
# Warning message:
# In `[<-.factor`(`*tmp*`, iris$Species == "virginica", value = c(1L,  :
#   invalid factor level, NAs generated

It will work if you first increase your factor levels:

levels(iris$Species) <- c(levels(iris$Species), "new.species")
iris$Species[iris$Species == 'virginica'] <- 'new.species'

If you want to replace "species A" with "species B" you'd be better off with

levels(iris$Species)[match("oldspecies",levels(iris$Species))] <- "newspecies"

User · Answer

In case you have to replace multiple values and if you don t mind  refactoring  your variable with as factor as character       you could try the following   replace values  lt - function search  replace  x     stopifnot length search     length replace     xnew  lt - replace  match x  search      takeOld  lt - is na xnew   amp   is na x    xnew takeOld   lt - x takeOld    return xnew     iris Species  lt - as factor search c  oldValue1   oldValue2                              replace c  newValue1   newValue2                              x as character iris Species

User · Answer

Using dlpyr  mutate and forcats  fct recode   library dplyr  library forcats   iris  lt - iris   gt       mutate Species   fct recode Species       Virginica     virginica        Versicolor     versicolor         iris   gt      count Species     A tibble  3 x 2      Species     n        lt fctr gt   lt int gt  1     setosa    50 2 Versicolor    50 3  Virginica    50

User · Answer

I had the same problem  This worked better   Identify which level you want to modify  levels iris Species        setosa   versicolor   virginica     So  setosa is the first   Then  write this        levels iris Species  1   lt - new name

User · Answer

For the things that you are suggesting you can just change the levels using the levels   levels iris Species  3   lt -  new

User · Answer

A more general solution that works with all the data frame at once and where you don t have to add new factors levels is   data mtx  lt - as matrix data df  data mtx which data mtx     old value to replace     lt -  new value  data df  lt - as data frame data mtx    A nice feature of this code is that you can assign as many values as you have in your original data frame at once  not only one  new value   and the new values can be random values  Thus you can create a complete new random data frame with the same size as the original

User · Answer

You can use the function revalue from the package plyr to replace values in a factor vector   In your example to replace the factor virginica by setosa    data iris   library plyr   revalue iris Species  c  virginica     setosa    - gt  iris Species

User · Answer

You want to replace the values in a dataset column  but you re getting an error like this       invalid factor level  NA generated   Try this instead   levels dataframe column  levels dataframe column    old value    lt -  new value

[r] Replace contents of factor column in R dataframe

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