[R] How to add a variable to a dataframe whose values are conditional upon the values of an existing variable

[Andrew Miles]

You could also try a series of simple ifelse statements.  I just tried  
the following and got it to work, though I am sure there is a faster  
way.

  t=c("cow", "dog", "chick")
  y=c(1,3,4)
mat=cbind(t,y)
mat=as.data.frame(mat)

 > mat
       t y
1   cow 1
2   dog 3
3 chick 4

mat$g=ifelse(mat$t=="cow", 1, 6)
mat$g=ifelse(mat$t=="dog", 2, mat$g)
mat$g=ifelse(mat$t=="chick", 3, mat$g)

 > mat
       t y g
1   cow 1 1
2   dog 3 2
3 chick 4 3

To days of the week would only be 7 statements.

Andrew Miles
Department of Sociology
Duke University

On Feb 26, 2010, at 2:31 PM, Steve Matco wrote:

> Hi everyone,
>
> I am at my wits end with what I believe would be considered simple  
> by a more experienced R user. I want to know how to add a variable  
> to a dataframe whose values are conditional on the values of an  
> existing variable. I can't seem to make an ifelse statement work for  
> my situation. The existing variable in my dataframe is a character  
> variable named DOW which contains abbreviated day names (SAT, SUN,  
> MON.....FRI). I want to add a numerical variable named DOW1 to my  
> dataframe that will take on the value 1 if DOW equals "SAT", 2 if  
> DOW equals "SUN", 3 if DOW equals "MON",.....,7 if DOW equals "FRI".
> I  know this must be a simple problem but I have searched everywhere  
> and tried everything I could think of. Any help would be greatly  
> appreciated.
>
> Thank you,
>
> Mike
>
>
>
>
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