R help - Oct 2009 - Using grep to determine value of last letter...

I am currently being defeated by grep.  I am attempting to determine the value
of the last letter of a character string.

An example of my data set is shown below.  Regarding the codes, I would like to
identify the value of the last character and then take the appropriate action,
e.g.
If the value is L then label UL rating XXX
It the value is F then label UL rating YYY
...

I assume it will be something like the following:
grep("last letter",  HousesWithCodes$Codes) 

Thanks again for any insights. 

BuildYear<-c(1980, 1985, 1975, 1990, 1980)
SqrFootage<-c(1500, 1650, 1500, 2000, 1450)
Exterior<-c("Brick", "Stone", "Siding",
"Brick", "Siding")

SubdivisionHouses<-data.frame(BuildYear, SqrFootage, Exterior)

Year<-c(1980, 1985, 1975, 1990, 1977, 1986)
Codes<-c("G2G1L", "G5L1F", "K1Y2G",
"G4B1B", "K1N3B", "K3M4X")
BuildingCodes<-data.frame(Year, Codes)

HousesWithCodes<-merge(SubdivisionHouses, BuildingCodes,
by.x="BuildYear", by.y="Year")

Well, regexpr() can do it; the magical incantation is 

regexpr(".$",yourstring)

See ?regexpr for details.

However, as your task really doesn't involve MATCHING characters, but
COUNTING characters, it might be simpler to use nchar() and substr():

n <- nchar(yourstring)
lastLetter <- substr(yourstring, n, n)


Bert Gunter
Genentech Nonclinical Biostatistics
 
 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
Behalf Of Jason Rupert
Sent: Monday, October 19, 2009 12:52 PM
To: R-help at r-project.org
Subject: [R] Using grep to determine value of last letter...

I am currently being defeated by grep.  I am attempting to determine the
value of the last letter of a character string.  

An example of my data set is shown below.  Regarding the codes, I would like
to identify the value of the last character and then take the appropriate
action, e.g. 
If the value is L then label UL rating XXX
It the value is F then label UL rating YYY
...

I assume it will be something like the following:
grep("last letter",  HousesWithCodes$Codes) 

Thanks again for any insights. 

BuildYear<-c(1980, 1985, 1975, 1990, 1980)
SqrFootage<-c(1500, 1650, 1500, 2000, 1450)
Exterior<-c("Brick", "Stone", "Siding",
"Brick", "Siding")

SubdivisionHouses<-data.frame(BuildYear, SqrFootage, Exterior)

Year<-c(1980, 1985, 1975, 1990, 1977, 1986)
Codes<-c("G2G1L", "G5L1F", "K1Y2G",
"G4B1B", "K1N3B", "K3M4X")
BuildingCodes<-data.frame(Year, Codes)

HousesWithCodes<-merge(SubdivisionHouses, BuildingCodes,
by.x="BuildYear",
by.y="Year")

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Here are several ways to find the last character in a string:
> x <- "abc"
> substring(x, nchar(x))
[1] "c"
> sub(".*(.)", "\\1", x)
[1] "c"
> library(gsubfn)
> strapply(x, ".$")[[1]]
[1] "c"

On Mon, Oct 19, 2009 at 3:52 PM, Jason Rupert <jasonkrupert at yahoo.com>
wrote:
> I am currently being defeated by grep. ?I am attempting to determine the
value of the last letter of a character string.
>
> An example of my data set is shown below. ?Regarding the codes, I would
like to identify the value of the last character and then take the appropriate
action, e.g.
> If the value is L then label UL rating XXX
> It the value is F then label UL rating YYY
> ...
>
> I assume it will be something like the following:
> grep("last letter", ?HousesWithCodes$Codes)
>
> Thanks again for any insights.
>
> BuildYear<-c(1980, 1985, 1975, 1990, 1980)
> SqrFootage<-c(1500, 1650, 1500, 2000, 1450)
> Exterior<-c("Brick", "Stone", "Siding",
"Brick", "Siding")
>
> SubdivisionHouses<-data.frame(BuildYear, SqrFootage, Exterior)
>
> Year<-c(1980, 1985, 1975, 1990, 1977, 1986)
> Codes<-c("G2G1L", "G5L1F", "K1Y2G",
"G4B1B", "K1N3B", "K3M4X")
> BuildingCodes<-data.frame(Year, Codes)
>
> HousesWithCodes<-merge(SubdivisionHouses, BuildingCodes,
by.x="BuildYear", by.y="Year")