Message-ID: <971536df0901251442r3337ba3ai7d30fdd3f72d113b@mail.gmail.com>
Date: 2009-01-25T22:42:34Z
From: Gabor Grothendieck
Subject: comparing the previous and next entry of a vector
In-Reply-To: <63CBE05F-D7CA-461E-9F14-B38063131B5A@licht-malerei.de>
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, J?rg Gro? <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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