Re: [R] regular expression for nth character in a string

From: David Winsemius <dwinsemius_at_comcast.net>
Date: Mon, 25 Apr 2011 06:47:00 -0400

On Apr 25, 2011, at 6:17 AM, Gonšalo Ferraz wrote:

> Hi, I have a string
>
> "InTrouble"
>
> and want to extract, say, the first two characters: "In"
> or the last three: "blee"
> or the 3rd, 4th, and 5th: "Trou"
>
> Is there an easy way of doing this quickly with regular expressions
> in gsub, grep or similar?

Not greppish but seems to be the obvious approach:

 > substr("Trouble", 1,2)
[1] "Tr"
 > substr("Trouble", 3,5)
[1] "oub"

The greppish ways:

 > sub("(^..)(.*$)", "\\1", "Troubles")
[1] "Tr"

 > sub("(^..)(...)(.*$)", "\\2", "Troubles") [1] "oub"
 > sub("(^..)(.{3})(.*$)", "\\2", "Troubles") [1] "oub"

-- 

David Winsemius, MD
West Hartford, CT

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Received on Mon 25 Apr 2011 - 10:48:59 GMT

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