[R] Advice on recoding a variable depending on another which contains NAs

[Anthony Staines]

Ah,
so that's how ifelse gets used...

Presumably if I had more than 2 non-missing values in the 
control variable, I could use it several times.

Thank you very much, for a really useful answer, and thanks 
for getting back so quickly!

All the best,
Anthony Staines

On 11/19/11 23:55, David Winsemius wrote:
>
> On Nov 19, 2011, at 6:31 PM, Anthony Staines wrote:
>
>
> This would seem to be an obvious task for ifelse()
>
> SCQScore <- NA
> d$SCQScore <- ifelse( SCQ1 == 1, d$SCQScore1, d$SCOScore2)
>
> (And don't use 99 for missing. Use NA. It will protect you
> better than "99".)
>
>
> I suppose you could enforce the two level testing with:
>
> d$SCQScore <- ifelse( SCQ1 == 1, d$SCQScore1,
> ifelse(SCQ1 ==2, d$SCOScore2, NA))
>
>>
>> d$SCQScore <- 99
>> ##Distinct value for any other values I've missed
>>
>> d$SCQScore[SCQ1 == 1] <- d$SCQScore1[SCQ1 == 1]
>> ## Talks using phrases/sentences, so sum S2CQ:SCQ40
>>
>> d$SCQScore[SCQ1 == 2] <- d$SCQScore2[SCQ1 == 2]
>> ## Can't do this, so sum SCQ8:SCQ40
>>
>> d$SCQScore[is.na(d$SCQ1)] <- d$SCQScore1 [is.na(d$SCQ1)]
>> ## SCQ1 is missing
>>
>> This fails on line 2
>> (d$SCQScore[SCQ1 == 1] <- d$SCQScore1[SCQ1 == 1])
>> with the error message
>> "NAs are not allowed in subscripted assignments",
>> presumably because SCQ1 does indeed contain missing values.
>>
>> This can be fixed, got around, or otherwise bypassed, by
>> creating a new variable SCQ1, with no missing values, as
>> shown :-
>>
>> SCQ1 <- d$SCQ1
>> SCQ1[is.na(SCQ1)] <- 3
>>
>> d$SCQScore[SCQ1 == 1] <- d$SCQScore1[SCQ1 == 1]
>> ## Talks using phrases/sentences so sum S2CQ:SCQ40
>> d$SCQScore[SCQ1 == 2] <- d$SCQScore2[SCQ1 == 2]
>> ## Can't do this, so sum SCQ8:SCQ40
>> d$SCQScore[SCQ1 == 3] <- d$SCQScore1[SCQ1 == 3]
>> ## We don't know if he/she can talk, so guess - sum S2:S40
>>
>> This type of thing is a common problem in my little world.
>> Is there a better/less klutzy/smarter way of solving it
>> than creating a new variable each time? Please bear in
>> mind that it is critical, for later analysis, to keep the
>> missing values in SCQ1.
>>
>> Best wishes,
>> Anthony Staines
>> --
>> Anthony Staines, Professor of Health Systems,
>> School of Nursing and Human Sciences, DCU, Dublin 9,Ireland.
>> Tel:- +353 1 700 7807. Mobile:- +353 86 606 9713
>> http://astaines.eu/
>> ______________________________________________
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>> PLEASE do read the posting guide
>> http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained,
>> reproducible code.
>
> David Winsemius, MD
> West Hartford, CT
>

-- 
Anthony Staines, Professor of Health Systems,
School of Nursing and Human Sciences, DCU, Dublin 9,Ireland.
Tel:- +353 1 700 7807. Mobile:- +353 86 606 9713
http://astaines.eu/