[R] R grep & gsub issue - sign seems to be causing an issue...

[Prof Brian Ripley]

On Thu, 12 Mar 2009, Duncan Murdoch wrote:

> Jason Rupert wrote:
>> I would like to use grep and gsub to manipulate a vector to make the names 
>> used consistent, i.e. reduce a level or two. 
>
> This is dangerous:  grep and gsub use regular expressions, so a lot of 
> characters (see ?regexp for the list) have special meanings.

Unless argument fixed=TRUE< which is often useful.

> For the kind of substitutions you want, just do things like
>
> newlist <- tmp_test
> newlist[newlist == tmp_test[2]] <- tmp_test[1]
>
> Duncan Murdoch
>> However, here is what I found when I attempted to use grep and gsub:
>> 
>>> tmp_test<-c("House 1 Plot Plus +100","House 2 Plot Plus +100","House 3 
>>> Plot Plus -100","House 4 Plot Plus -100","House 1 Plus +100","House 2 Plus 
>>> +100","House 3 Plus -100","House 4 Plus -100")
>>> 
>>
>> 
>>> gsub(tmp_test[2], tmp_test[1], tmp_test)
>>> 
>> [1] "House 1 Plot Plus +100" "House 2 Plot Plus +100" "House 3 Plot Plus 
>> -100" "House 4 Plot Plus -100" "House 1 Plus +100"      "House 2 Plus +100" 
>> [7] "House 3 Plus -100"      "House 4 Plus -100"
>> 
>>> grep(tmp_test[1],tmp_test)
>>> 
>> integer(0)
>> 
>> However, 
>>> gsub(tmp_test[3], tmp_test[1], tmp_test)
>>> 
>> [1] "House 1 Plot Plus +100" "House 2 Plot Plus +100" "House 1 Plot Plus 
>> +100" "House 4 Plot Plus -100" "House 1 Plus +100"      "House 2 Plus +100" 
>> [7] "House 3 Plus -100"      "House 4 Plus -100"
>> 
>> Thanks for any feedback that can be provided.
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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