R help - Feb 2008 - how to extract characters from a character string

Hi, I ran into a problem when I complied a dataset with UTM coordinates.
For calculating distances between sites, I need to reformat the
coordinates from, for example,

 

32?35.421 N, to 35.421, i.e. I need to delete all digits before symbol ?
and a space and N at the end of the string. What functions I should use?


 

Thanks in advance. 

 

 

Weidong Gu, 

Department of Medicine
University of Alabama, Birmingham



 


	[[alternative HTML version deleted]]

Hi Weidong,

It works, but I'm completely sure could be more efficient:

# x is a string
DELETE=function(x){
x=as.character(x)
res=NULL; for(i in 1:nchar(x)) res=c(res,substr(x,i,i))
pos=which(res=="?"|res==" ")  # Detecting "?" and 
"  "
res2=res[(pos[1]+1):(pos[2]-1)]
k=length(res2)
res3=NULL; for(i in 1:k) res3=paste(res3,res2[i],sep="")
as.numeric(RS)
}
> DELETE("32?35.421 N")
[1] 35.421

I hope this helps.


Jorge



On 2/8/08, Weidong Gu <wgu@uab.edu> wrote:
>
> Hi, I ran into a problem when I complied a dataset with UTM coordinates.
> For calculating distances between sites, I need to reformat the
> coordinates from, for example,
>
>
>
> 32?35.421 N, to 35.421, i.e. I need to delete all digits before symbol ?
> and a space and N at the end of the string. What functions I should use?
>
>
>
>
> Thanks in advance.
>
>
>
>
>
> Weidong Gu,
>
> Department of Medicine
> University of Alabama, Birmingham
>
>
>
>
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
	[[alternative HTML version deleted]]

This should do it for you:
> x
[1] "32?35.421 N"
> sub("^.*?([[:digit:].]+) N", "\\1", x, perl=TRUE)
[1] "35.421"
>

On 2/8/08, Weidong Gu <wgu at uab.edu> wrote:
> Hi, I ran into a problem when I complied a dataset with UTM coordinates.
> For calculating distances between sites, I need to reformat the
> coordinates from, for example,
>
>
>
> 32?35.421 N, to 35.421, i.e. I need to delete all digits before symbol ?
> and a space and N at the end of the string. What functions I should use?
>
>
>
>
> Thanks in advance.
>
>
>
>
>
> Weidong Gu,
>
> Department of Medicine
> University of Alabama, Birmingham
>
>
>
>
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

Match the start (^) followed by anything (.*)
to the question mark ([?]) or (|) a space ( ) followed
by anything (.*) to the end ($) and replace each
of those with nothing ("").

gsub("^.*[?]| .*$", "", "32?35.421 N")


On Feb 8, 2008 3:36 PM, Weidong Gu <wgu at uab.edu>
wrote:
> Hi, I ran into a problem when I complied a dataset with UTM coordinates.
> For calculating distances between sites, I need to reformat the
> coordinates from, for example,
>
>
>
> 32?35.421 N, to 35.421, i.e. I need to delete all digits before symbol ?
> and a space and N at the end of the string. What functions I should use?
>
>
>
>
> Thanks in advance.
>
>
>
>
>
> Weidong Gu,
>
> Department of Medicine
> University of Alabama, Birmingham
>
>
>
>
>
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

Weidong Gu wrote:
> Hi, I ran into a problem when I complied a dataset with UTM coordinates.
> For calculating distances between sites, I need to reformat the
> coordinates from, for example,
>
>  
>
> 32?35.421 N, to 35.421, i.e. I need to delete all digits before symbol ?
> and a space and N at the end of the string. What functions I should use?
>
>
>   
One of the regexpr family. Beware that this stuff can be quite 
maddening, but here's one option:

 > x <- "32?35.421 N"
 > sub("^.*\\?([.0-9]*) N$", "\\1", x)
[1] "35.421"

or less general but more straightforward:

 > sub(" N$", "", sub("^.*\\?", "",
x))
[1] "35.421"

>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>   

-- 
   O__  ---- Peter Dalgaard             ?ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907