Question

Any suggestions on the best logic to create a new variable in a r data frame that is contingent on other variables in the dataframe?

Essentially, I have a type variable in one data frame that I want to overide in certian instances which are contained in a second dataframe. Below is some sample data:

#### original data frame
id=c(1,2,3,4,5,6)
type=c("O", "O", "G", "O", "G", "O")
qty=c(10,20,30,40,50,60)
df1=data.frame(id, type, qty)

#### new dataframe with type override
id=c(2,4)
type_override=c("G", "G")
df2=data.frame(id,type_override)

#### dataframe with both origional and override type
df3=merge(df1, df2, by=c("id"), all.x=TRUE)

#### create new type variable that uses "type" for all variables
#### unless "type_override" calls for a override
df3$type_new= ???????

I would like to use the type classification (i.e. “type_override”) in the second dataframe to override the type classification (i.e. “type” in the first dataframe.

I am an Excel user that is trying to make the transition to R, in Exel, I would just do something like:

type_newC1 = if(isna(type_overrideB1),typeA1,type_overrideB1)

Any assistance would be greatly appreciated.

Answer 1

If your df2 will be used with only a single type, you can get away with a single step:

df1$type_override <- ifelse(df1$id %in% df2$id, df2$type_override, df1$type)