[R] correction to the previously asked question (about merging factors)

[Spencer Graves]

      Sundar:  Your solution is not only more elegant than mine, it's 
also faster, at least with this tiny example: 

 > start.time <- proc.time()
 > k1 <- length(F1)
 > k2 <- length(F2)
 > F12.lvls <- unique(c(levels(F1), levels(F2)))
 > F. <- factor(rep(F12.lvls[1], k1+k1), levels=F12.lvls)
 > F.[1:k1] <- F1
 > F.[-(1:k1)] <- F2
 > proc.time()-start.time
[1] 0.00 0.00 0.42   NA   NA
 >
 > start.time <- proc.time()
 > F1 <- factor(c("b", "a"))
 > F2 <- factor(c("c", "b"))
 > F3 <- factor(c(levels(F1)[F1], levels(F2)[F2]))
 > proc.time()-start.time
[1] 0.00 0.00 0.24   NA   NA
 >
      With longer vectors, mine may be faster -- but yours is still more 
elegant. 

      Best Wishes,
      spencer graves

Sundar Dorai-Raj wrote:

> How about simply
>
> F1 <- factor(c("b", "a"))
> F2 <- factor(c("c", "b"))
> F3 <- factor(c(levels(F1)[F1], levels(F2)[F2]))
>
> -sundar
>
> Spencer Graves wrote:
>
>>      What about the following:
>>  > F1 <- factor(c("b", "a"))
>>  > F2 <- factor(c("c", "b"))
>>  > k1 <- length(F1)
>>  > k2 <- length(F2)
>>  > F12.lvls <- unique(c(levels(F1), levels(F2)))
>>  > F. <- factor(rep(F12.lvls[1], k1+k1), levels=F12.lvls)
>>  > F.[1:k1] <- F1
>>  > F.[-(1:k1)] <- F2
>>  > F.
>> [1] b a c b
>> Levels: a b c
>>
>>      This saves converting the factors to characters, which might 
>> save computer time at the expense of your time.      hope this 
>> helps.      spencer graves
>>
>> Svetlana Eden wrote:
>>
>>> I have two factors l1, l2, and I'd like to merge them.
>>>
>>> (Remark:       The factors can not be converted to charaters)
>>>
>>> Function c() does not give me the result I want:
>>>
>>>
>>>  
>>>
>>>> l1 = factor(c('aaaa', 'bbbb'))
>>>> l2 = factor(c('ccc', 'dd'))
>>>> lMerge = factor(c(l1, l2))
>>>> lMerge
>>>>   
>>>
>>>
>>> [1] 1 2 1 2
>>> Levels: 1 2
>>>  
>>>
>>> I'd like to merge l1 and l2 and to get lMerge 
>>> ----------------------------------------------
>>>
>>> [1] aaaa bbbb ccc dd
>>> Levels: aaaa bbbb ccc dd
>>>
>>> instead of ----------
>>>
>>> [1] 1 2 1 2
>>> Levels: 1 2
>>>  
>>>
>>>
>>> How should I do that without converting the factors back to strings.
>>> -------------------------------------------------------------------
>>>
>>>  
>>>
>>
>> ______________________________________________
>> R-help at stat.math.ethz.ch mailing list
>> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide! 
>> http://www.R-project.org/posting-guide.html
>
>