[R] If statement - copying a factor variable to a new variable

[Rui Barradas]

Hello,

Another way is to use index vectors:


v1.factor <- c("S","S","D","D","D",NA)
v2.factor <- c("D","D","S","S","S","S")

td2 <- test.data <- data.frame(v1.factor,v2.factor)

for (i in 1:nrow(test.data) ) {

     [... etc ...]

} #End FOR

# Create index vectors
na1 <- is.na(v1.factor)
na2 <- is.na(v2.factor)

# Create 'newvar' with default value
td2$newvar <- NA
# Now, set values if condition is met.
td2$newvar[!na1 & !na2] <- as.character(td2$v1.factor[!na1 &!na2])

all.equal(test.data, td2)
[1] TRUE


I find this way better when doing a multiple if/else based on 
combinations of a small number of conditions. It's also very readable.

Hope this helps,

Rui Barradas

Em 28-06-2012 08:00, Miguel Manese escreveu:
> Hi James,
>
> On Thu, Jun 28, 2012 at 12:33 AM, James Holland <holland.aggie at gmail.com> wrote:
>> I need to look through a dataset with two factor variables, and depending
>> on certain criteria, create a new variable containing the data from one of
>> those other variables.
>>
>> The problem is, R keeps making my new variable an integer and saving the
>> data as a 1 or 2 (I believe the levels of the factor).
>>
>> I've tried using as.factor in the IF output statement, but that doesn't
>> seem to work.
>>
>> Any help is appreciated.
>>
>>
>>
>> #Sample code
>>
>> rm(list=ls())
>>
>>
>> v1.factor <- c("S","S","D","D","D",NA)
>> v2.factor <- c("D","D","S","S","S","S")
>>
>> test.data <- data.frame(v1.factor,v2.factor)
>
> The vectorized way to do that would be
>
> # v1.factor if present, else v2.factor
> test.data$newvar <- ifelse(!is.na(v1.factor), v1.factor, v2.factor)
>
> I suggest you work with the character levels first then convert it
> into a factor, e.g. if v1.factor & v2.factor are already factors, do:
>
> test.data$newvar <- as.factor(ifelse(!is.na(v1.factor),
> as.character(v1.factor), as.character(v2.factor)))
>
>
>
> Regards,
>
> Jon
>
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