Many thanks for your elaborated explaina.








At 2012-01-13 11:34:51,"R. Michael Weylandt" <michael.weylandt@gmail.com> wrote:
>As Jorge noted, the fix is to use "%in%": a fuller explanation of why
>`==` didn't work is that it implicitly used vector recycling: look at
>
>with(data, id == c("a", "c"))
>
>implicitly, this expands to id == c("a","c", "a", "c") to get the
>lengths to match. Obviously only the first elements work here.
>
>But when you had c("a", "d") it expanded to c("a","d", "a", "d") and
>you get TRUE for the 1st and 4th slot. This, however, was just a lucky
>coincidence. Had you used c("d", "a") there would have been no
>matches.
>
>Anyways, definitely use %in% but hopefully this clarifies things.
>
>Michael
>
>On Thu, Jan 12, 2012 at 9:50 PM, Jorge I Velez <jorgeivanvelez@gmail.com> wrote:
>> Hi,
>>
>> Use %in% instead of ==.
>>
>> HTH,
>> Jorge.-
>>
>>
>> On Thu, Jan 12, 2012 at 9:36 PM, ГПРА <> wrote:
>>
>>> Hi all
>>> I have a question about "subset" function.
>>>
>>>
>>> > dat
>>>  id x1 x2  x3
>>> 1  a  1 11 111
>>> 2  b  2 22 222
>>> 3  c  3 33 333
>>> 4  d  4 44 444
>>>
>>>
>>> > subset(dat,id==c("a","c"))
>>>  id x1 x2  x3
>>> 1  a  1 11 111
>>>
>>> > subset(dat,id==c("a","d"))
>>>  id x1 x2  x3
>>> 1  a  1 11 111
>>> 4  d  4 44 444
>>>
>>>
>>> >From the above, if I choose id=a,c, the result is wrong,but if I choose
>>> id=a,d, the result is right.
>>>
>>>
>>> What's the reason for it?
>>>
>>>
>>>
>>>
>>> Many thanks!
>>>
>>>
>>>
>>>
>>> My best
>>>
>>>
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>>>
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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.
>>>
>>
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>>
>>
>> ______________________________________________
>> R-help@r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>>

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