As the help page says:
'&' and '&&' indicate logical AND and '|' and '||' indicate
logical OR. The shorter form performs elementwise comparisons in
much the same way as arithmetic operators. The longer form
evaluates left to right examining only the first element of each
vector. Evaluation proceeds only until the result is determined.
The longer form is appropriate for programming control-flow and
typically preferred in 'if' clauses.
so your results are what I'd expect.
Ted.
[EMAIL PROTECTED] wrote on 04/02/2007 05:17 PM:
> "&&" seems to behave strangely and gives different results from "&" e.g. in a
> data frame selection (regardless whether terms are bracketed)?
>
> ===========Script=======================
>
> test=data.frame(gender=c("F","M","M","F","F"),side=c("R","L","R","L","R"))
> test
> test[test$gender=="F" & test$side=="R",]
> test[test$gender=="F" && test$side=="R",]
>
> =============Output:=====================
>
>> test=data.frame(gender=c("F","M","M","F","F"),side=c("R","L","R","L","R"))
>> test
>>
> gender side
> 1 F R
> 2 M L
> 3 M R
> 4 F L
> 5 F R
>
>> test[test$gender=="F" & test$side=="R",]
>>
> gender side
> 1 F R
> 5 F R
>
>> test[test$gender=="F" && test$side=="R",]
>>
> gender side
> 1 F R
> 2 M L
> 3 M R
> 4 F L
> 5 F R
>
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>
--
Dr E.A. Catchpole
Visiting Fellow
Univ of New South Wales at ADFA, Canberra, Australia
_ and University of Kent, Canterbury, England
'v' - www.pems.adfa.edu.au/~ecatchpole
/ \ - fax: +61 2 6268 8786
m m - ph: +61 2 6268 8895
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