[R] comparing the previous and next entry of a vector

[Jörg Groß]

is there a way to do that without generating a data.frame?

In my real data, I have a big data.frame and I have to compare over  
different columns...


Am 25.01.2009 um 23:42 schrieb Gabor Grothendieck:

> Try this:
>
>> DF <- data.frame(x, nxt = c(tail(x, -1), NA), prv = c(NA, head(x,  
>> -1)))
>> DF
>  x nxt prv
> 1 1   2  NA
> 2 2   3   1
> 3 3   4   2
> 4 4   5   3
> 5 5   2   4
> 6 2   6   5
> 7 6  NA   2
>> subset(DF, nxt == 3 & prv == 1)$x
> [1] 2
>
>
> On Sun, Jan 25, 2009 at 5:29 PM, Jörg Groß <joerg at licht-malerei.de>  
> wrote:
>> Hi,
>>
>> I have a quit abstract problem, hope someone can help me here.
>>
>> I have a vector like this:
>>
>>
>> x <- c(1,2,3,4,5,2,6)
>> x
>>
>> [1] 1 2 3 4 5 2 6
>>
>> now I want to get the number where the previous number is 1 and the  
>> next
>> number is 3
>> (that is the 2 at the second place)
>>
>> I tried something with tail(x, -1) ...
>> with that, I can check  the next number, but how can I check the  
>> previous
>> number?
>>
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