How to create a new variable based on parts of another character variable: A generalization

... Well, this works in this simple case, but is too clumsy for a 

formulation of this problem:  given a "dictionary" consisting of two 
character vectors of unique "names" (or two columns in a data frame), x 
and y,  how does one convert a factor z with levels in x into the 
corresponding equivalent with levels in y?

There are likely a zillion ways to do this with various packages and 
functions, but the simplest and most straightforward must surely be:  

Example:

x <- LETTERS[1:4]
y <- LETTERS[5:8]
z <- factor(sample(x,15, rep=TRUE))
z

 [1] B D A C B A B D A D D A A D B
Levels: A B C D

factor(y[z])

 [1] F H E G F E F H E H H E E H F
Levels: E F G H

This is a nice example of the utility of the factor data structure, 

tends to get dissed a lot, because it can badly burn you if you're not 
careful with it.

A fuller discussion of these issues can be found by searching 
on"associative arrays"  or "hashes", of which factors are an elementary 

-- Bert

On Mon, Oct 24, 2011 at 6:00 AM, Petr PIKAL <petr.pikal at precheza.cz> 

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 

UFT occurs in the variable A, then the variable D shall be "Boreal" 

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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