How to convert a factor to numeric in a predefined order in R

Question

I have a factor column, with three values: "b", "c" and "free".

I did

df$new_col = as.numeric (df$factor_col)

But it will convert "b" to 1, "c" to 2 and "free" to 3.

But I want to convert "free" to 0, "b" to 2 and "c" to 5. How can I do it in R?

Thanks a lot

Answer 1

f <- factor(c("b", "c", "c", "free", "b", "free"))

You can try renaming the factor levels,

levels(f)[levels(f)=="b"] <- 2
levels(f)[levels(f)=="c"] <- 5
levels(f)[levels(f)=="free"] <- 0
> f
#[1] 2 5 5 0 2 0
#Levels: 2 5 0

Answer 2

One option would be to call the 'factor' again and specify the levels and labels argument based on the custom order and change to numeric after converting to 'character' or through the levels

 df$new_col <- as.numeric(as.character(factor(df$factor_col,
               levels=c('b', 'c', 'free'), labels=c(2, 5, 0))))

Another option is recode from library(car) . The output will be factor class. If we need to convert to 'numeric', we can do this as in the earlier solution ( as.numeric(.. ).

library(car)
df$new_col <- with(df, recode(factor_col, "'b'=2; 'c'=5; 'free'=0"))

data

df <- data.frame(factor_col= c('b', 'c', 'b', 'free', 'c', 'free'))

Answer 3

You can use the following approach to create the new column:

# an example data frame
f <- data.frame(factor_col = c("b", "c", "free"))  

# create new_col    
f <- transform(f, new_col = (factor_col == "b") * 2 + (factor_col == "c") * 5)

The result ( f ):

  factor_col new_col
1          b       2
2          c       5
3       free       0