[R] How to generate a new factor variable by two other factor variables

[Shuguang Sun]

Thanks. It works :)

Shuguang

On Wed, Nov 5, 2008 at 12:24 AM, Marc Schwartz
<marc_schwartz at comcast.net> wrote:
> The easiest way is probably to use interaction():
>
>> df
>  factorA factorB
> 1       0       0
> 2       0       0
> 3       1       0
> 4       0       1
> 5       1       1
>
>
> # Note the default separator of '.'
> df$factorC <- with(df, interaction(factorA,  factorB))
>
>> df
>  factorA factorB factorC
> 1       0       0     0.0
> 2       0       0     0.0
> 3       1       0     1.0
> 4       0       1     0.1
> 5       1       1     1.1
>
>
> If you want numeric values, you can adjust as follows:
>
> df$factorC <- factor(as.numeric(df$factorC) - 1)
>
>> df
>  factorA factorB factorC
> 1       0       0       0
> 2       0       0       0
> 3       1       0       1
> 4       0       1       2
> 5       1       1       3
>
>
> The latter step takes advantage of the underlying numeric nature of the
> factor levels and subtracts 1, since they are 1 based, not 0 based.
>
> See ?interaction
>
> HTH,
>
> Marc Schwartz
>
>
> on 11/04/2008 10:10 AM Jorge Ivan Velez wrote:
>> Dear Shuguang,
>> Here are two ways. Perhaps they are not efficient enough, but the work:
>>
>>
>> # Data
>> mydata=read.table(textConnection("
>> factorA factorB
>>    0       0
>>    0       0
>>    1       0
>>    0       1
>>    1       1"),header=TRUE)
>> closeAllConnections()
>>
>> # Option 1
>> mydata$factorC=as.factor(
>> apply(mydata,1,function(x){
>> paste(x,sep="",collapse="")
>> }
>> ))
>> levels(mydata$factorC)<-list("0"="00", "1"="10", "2"="01","3"="11")
>> mydata
>>
>> # Option 2
>> # You'll need to read the data again to see how this option works
>> mydata$factorC<-apply(mydata,1,function(x){
>> ifelse(sum(x)==0,0,
>> ifelse(x[1]==1 & x[2]==0,1,
>> ifelse(x[1]==0 & x[2]==1,2,3)))
>> }
>> )
>>
>> mydata
>>
>>
>> HTH,
>>
>>
>> Jorge
>>
>>
>>
>> On Tue, Nov 4, 2008 at 10:29 AM, Shuguang Sun <shuguang at gmail.com> wrote:
>>
>>> How to generate a new factor variable by two other factor variables?
>>>
>>> For example, if I have two factor variables, factorA and factorB,
>>> factorA factorB
>>>    0       0
>>>    0       0
>>>    1       0
>>>    0       1
>>>    1       1
>>>
>>> Is there a simple way to generate a new 4-levels factor variable as
>>>
>>> factorC factorA factorB
>>>    0      0       0
>>>    0      0       0
>>>    1      1       0
>>>    2      0       1
>>>    3      1       1
>>>
>>> --
>>> Shuguang Sun
>>> Fudan University, China
>>>
>