R help - Oct 2009 - gsub - replace multiple occurences with different strings

Hi,

I search a way to replace multiple occurrences of a string with  
different strings
depending on the place where it occurs.


I tried the following;

x <- c("xx y e d xx e t f xx e f xx")
x <- gsub("xx", c("x1", "x2", "x3",
"x4"), x)


what I want to get is;

x x1 y y e d x2 e t f x3 e f x4


but what I get is;

x x1 y y e d x1 e t f x1 e f x1
	[[alternative HTML version deleted]]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Martin Batholdy
> Sent: Monday, October 05, 2009 7:34 AM
> To: r help
> Subject: [R] gsub - replace multiple occurences with different strings
> 
> Hi,
> 
> I search a way to replace multiple occurrences of a string with  
> different strings
> depending on the place where it occurs.
> 
> 
> I tried the following;
> 
> x <- c("xx y e d xx e t f xx e f xx")
> x <- gsub("xx", c("x1", "x2",
"x3", "x4"), x)
> 
> 
> what I want to get is;
> 
> x > x1 y y e d x2 e t f x3 e f x4
You have a doubled y in the output but not the input,
I'll assume the input is correct.  I extended x to three similar
strings:

  x <- c("xx y e d xx e t f xx e f xx",
           "xx y e d xx e t f xx",
           "xx y e d xx e t f xx e f xxxx y e d xx e t f xx e f xx")

If you know you always have 4 xx's you can use sub (or gsub),
but it doesn't work properly if there are not exactly 4 xx's:
  > sub("xx(.*)xx(.*)xx(.*)xx", "x1\\1x2\\2x3\\3x4", x)
  [1] "x1 y e d x2 e t f x3 e f x4"                           
  [2] "xx y e d xx e t f xx"                                  
  [3] "x1 y e d xx e t f xx e f xxxx y e d x2 e t f x3 e f x4"
  
You can use gsubfn() from package gsubfn along with a function that
maintains
a count of how many times it has been called, as in
  > gsubfn("xx",
local({n<-0;function(x){n<<-n+1;paste(x,n,sep="")}}),
x)
  [1] "xx1 y e d xx2 e t f xx3 e f xx4"

  [2] "xx5 y e d xx6 e t f xx7"

  [3] "xx8 y e d xx9 e t f xx10 e f xx11xx12 y e d xx13 e t f xx14 e f
xx15"

If you want the count to start anew with each string in the vector you
can use sapply.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  



> 
> 
> but what I get is;
> 
> x > x1 y y e d x1 e t f x1 e f x1
> 	[[alternative HTML version deleted]]
> 
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