[R] ifelse function

[Min (Tilda) Zhang]

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