Message-ID: <XFMail.090125225516.Ted.Harding@manchester.ac.uk>
Date: 2009-01-25T22:55:16Z
From: (Ted Harding)
Subject: comparing the previous and next entry of a vector
In-Reply-To: <63CBE05F-D7CA-461E-9F14-B38063131B5A@licht-malerei.de>
On 25-Jan-09 22:29:25, J?rg Gro? 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?
x <- c(1,2,3,4,5,2,6)
x0 <- x[1:(length(x)-2)]
x1 <- x[3:(length(x))]
x[which((x0==1)&(x1==3))+1]
# [1] 2
Or, changing the data:
x <- c(4,5,1,7,3,2,6,9,8)
x0 <- x[1:(length(x)-2)]
x1 <- x[3:(length(x))]
x[which((x0==1)&(x1==3))+1]
# [1] 7
Ted.
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Date: 25-Jan-09 Time: 22:47:15
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