Hi Min,
You don't need to loop.
Since your column "g" is a factor variable,
it already has integer values 'under the covers'.
> pth <- data.frame(g =
c("sh","ao","ao","sh","iy","dcl","dcl","aa","iy","iy","aa","sh","ao","ao"))
>
> pth
g
1 sh
2 ao
3 ao
4 sh
5 iy
6 dcl
7 dcl
8 aa
9 iy
10 iy
11 aa
12 sh
13 ao
14 ao> class(pth$g)
[1] "factor"
You can get the factor integer values in a couple of ways:
e.g.
> pth$gn <- as.integer(pth$g)
> pth$gn
[1] 5 2 2 5 4 3 3 1 4 4 1 5 2 2
See help("factor") for some discussion of factor
variables and their components.
Another way:
> unclass(pth$g)
[1] 5 2 2 5 4 3 3 1 4 4 1 5 2 2
attr(,"levels")
[1] "aa" "ao" "dcl" "iy"
"sh" >
Hope this helps
Best
Steven McKinney
-----Original Message-----
From: r-help-bounces at r-project.org on behalf of Min (Tilda) Zhang
Sent: Tue 11/27/2007 7:45 PM
To: r-help at r-project.org
Subject: [R] ifelse function
Hi there,
I need help with IFELSE function.
The column g of my dataset pth, pth$g consists of "aa",
"ao", "dcl", "iy",
"sh".
The last few values of pth$g looks like:
[4496] sh ao ao sh iy dcl dcl aa iy iy aa sh ao ao
Levels: aa ao dcl iy sh
I want to convert these values into 1,2,3,4,5. I tried to use a loop and I
found the following statement did not work.> pth$g[1]<-ifelse(pth$g[1]=="aa",1,pth$g[1])
Warning message:
invalid factor level, NAs generated in: `[<-.factor`(`*tmp*`, 1, value = 5L)
Then I tried this statement. It works, but I do not understand how it
convert the values not only into 1 but also into 2,3,4,5 at the same time.
> pth$g<-ifelse(pth$g=="aa",1,pth$g)
> pth$g
[1] 4 4 3 3 1 4 1 5 ....
I appreciate your help.
Min (Tilda) Zhang
Department of Statistics
North Carolina State University
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