[R] Changing some values within a variable

[Toni Pitcher]

Hi

I'm new to R and would like some help with a couple of problems. I 
suspect the solutions are quite simple.

I have a data.frame (data) with 40 variables and 5238 observations 
created from ~150 text files using read.table.

I would like to change some of the entries within two different columns.

Firstly, in the Group column I have groups A and B, I would like to 
select all As and change to C. I have tried the following;

data$Group = ifelse(data$Group == 'A', "C", data$Group)
data$Group <- as.factor(data$Group)

This works to some extent, all As have been changes to Cs, but the Bs 
have also been changed, in this case to "2", instead of remaining as 
their original values. How do I get the Bs to stay the same?


Second problems is similar;

I need to change some of the Subject IDs. The required format is 3 
numbers followed by 3 letters (999LLL). Some of the IDs have format 
999LLL-LL, Thus I need to delete the -LL from the IDs.
How do I generically specify "find 999LLL-LL and replace with 999LLL"?


Many thanks in advance

Toni




-- 
Toni Pitcher PhD
Dept. of Medicine
University of Otago, Christchurch

Van der Veer Institute for Parkinson's and Brain Research
66 Stewart St 
Christchurch 8011
New Zealand

Phone: +64 3 378 6075 (internal extn 86075)
Email: toni.pitcher at otago.ac.nz