R create new column based on if else condition

Question

I have a data frame consisting of n column and one of them is food . food column possible values are apple , tomato , cabbage , sausage , beer , vodka , potato . I want to create a new column in my data data frame as follows: if food==apple or food==tomato or food==potato , then assign vegetables , otherwise assign just data$food value.

So, if data frame is like this:

ID ..(some other columns).. food

1                           apple
2                           sausage
3                           tomato
4                           cabbage
5                           vodka

then the result should be as follows:

ID ..(some other columns).. food        category

1                           apple       vegetable
2                           sausage     sausage
3                           tomato      vegetable
4                           cabbage     vegetable
5                           vodka       vodka

How can I do that?

Answer 1

I would copy the variable and find which rows correspond to your criterion and replace the values only for those rows. I also added a new factor level for tidy bookkeeping.

xy <- data.frame(food = sample(c("apple", "tomato", "cabbage", "sausage", "beer", "vodka", "potato"), 50, replace = TRUE))

xy$newcol <- xy$food
levels(xy$newcol) <- c(levels(xy$newcol), "veggy")
xy[xy$food %in% c("apple", "tomato", "potato"), "newcol"] <- "veggy"
xy

      food  newcol
1    apple   veggy
2    vodka   vodka
3  sausage sausage
4  cabbage cabbage
5    vodka   vodka
6   potato   veggy
7  cabbage cabbage
8  cabbage cabbage
...

Answer 2

You could use recode from car , which will work with both 'character' and 'factor' column. For 'factor' columns, the unused levels are dropped while new levels are added.

library(car)
xy$newcol <- recode(xy$food, "c('apple', 'tomato', 'potato')='veggy'")

NOTE: xy from @Roman Lustrik's post

If you are using data.table , this can be done with (updating the same column)

library(data.table)
setkey(setDT(xy), food)[J(c('apple', 'tomato', 'potato')), food:='veggy']

Answer 3

What about this?

# df is your data frame
veg <- c("tomato", "apple", "potato")
df$category <- ifelse(df$food %in% veg, "vegetable", df$food)