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 · 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 <- as.matrix(data.df)
data.mtx[which(data.mtx == "old.value.to.replace")] <- "new.value"
data.df <- 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

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

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

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

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   quot setosa quot       quot versicolor quot   quot virginica quot    Your example was bad  this works  iris Species iris Species     virginica    lt -  setosa   This is what more likely creates the problem you were seeing with your own data  iris Species iris Species     virginica    lt -  new species    Warning message    In    lt - factor    tmp    iris Species     quot virginica quot   value   c 1L         invalid factor level  NAs generated  It will work if you first increase your factor levels  levels iris Species   lt - c levels iris Species    quot new species quot   iris Species iris Species     virginica    lt -  new species    If you want to replace  quot species A quot  with  quot species B quot  you d be better off with levels iris Species  match  quot oldspecies quot  levels iris Species     lt -  quot newspecies quot

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

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

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

[r] Replace contents of factor column in R dataframe

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