How to create a new variable based on parts of another character variable.

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Hello,
I am just starting with R and I am having a (most probably) stupid problem by creating a new variable in a data.frame based on a part of another character variable.

I have a data frame like this one:

A			B 		C
AWI-test1	1		i
AWI-test5	2		r
AWI-tes75	56		z
UFT-2		5		I
UFT56		f		t
UFT356		9j		t
etc. etc.		89		t

I now want to look in the variable A if the string AWI is present and then create a variable D and putting "Arctic" inside. However, if the string UFT occurs in the variable A, then the variable D shall be "Boreal" etc. etc.

The resulting data.frame file should look like
A			B 		C	D
AWI-test1	1		i	Arctic	
AWI-test5	2		r	Arctic
AWI-tes75	56		z	Arctic
UFT-2		5		I	Boreal
UFT56		f		t	Boreal
UFT356		9j		t	Boreal
etc. etc.		89		t

Hi Philipp,
Since you mentioned that you were just starting with R, it might be a 
little optimistic to throw you into the regular expression cage and 
expect you to emerge unscathed. You can do this by constructing a 2 
column matrix or data frame of replacement values:

replacements<-matrix(c("AWI","UFT","Arctic","Boreal"),ncol=2)
replacements
      [,1]  [,2]
[1,] "AWI" "Arctic"
[2,] "UFT" "Boreal"

Then write a function using grep to replace the values:

swapLabels<-function(x,y) {
  for(swaprow in 1:dim(y)[1])
   if(length(grep(y[swaprow,1],x))) return(y[swaprow,2])
  return(NA)
}

Finally, apply the function to the first row of the data frame:

pf.df$D<-unlist(lapply(pf.df[,1],swapLabels,replacements))
pf.df$D
[1] "Arctic" "Arctic" "Arctic" "Boreal" "Boreal" "Boreal"

Jim
Hi

If you want to get rid of regular expressions at all and your A values 
start AWI for Arctic and UFT for boreal you can

DF$D <- ifelse(substr(DF$A, 1,1) == "A", "Arctic", "Boreal")

Regards
Petr
Hello,
I am just starting with R and I am having a (most probably) stupid 
problem
by creating a new variable in a data.frame based on a part of another 
character variable.

I have a data frame like this one:

A         B       C
AWI-test1   1      i
AWI-test5   2      r
AWI-tes75   56      z
UFT-2      5      I
UFT56      f      t
UFT356      9j      t
etc. etc.      89      t

I now want to look in the variable A if the string AWI is present and 
then
create a variable D and putting "Arctic" inside. However, if the string 
UFT occurs in the variable A, then the variable D shall be "Boreal" etc. 
etc.
The resulting data.frame file should look like 
A         B       C   D
AWI-test1   1      i   Arctic 
AWI-test5   2      r   Arctic
AWI-tes75   56      z   Arctic
UFT-2      5      I   Boreal
UFT56      f      t   Boreal
UFT356      9j      t   Boreal
etc. etc.      89      t

I know how to do this when I want to look for the entire string of A 
means
when there is "AWI-test1" and then create the variable D with "Arctic" 
but
not how to look only for a substring in A?
Would be great if somebody might help.
Thanks
Philipp

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