[R] Flummoxed by gsub().

[Rolf Turner]

I have a vector (say "x") of the form

     [1] "mung5"  "mung10" "mung20" "gorp5"  "gorp10" "gorp20"

I want to extract just the numbers (strings of digits) that appear at 
the end of the strings in "x".

My reading of ?regex led me to believe that

     gsub("[:alpha:]","",x)

should give the result that I want.  However it returns

     [1] "mung5"  "mung10" "mung20" "gor5"   "gor10"  "gor20"

i.e. it chops the last letter out of the "gorp" string, but nothing else.

I am completely bewildered by this behaviour and can see no rationale 
for it nor any way to adjust my syntax to get what I want.

A bit of Googling led me to the information that

     gsub("\\D","",x)

should work, and indeed it does, giving:

     [1] "5"  "10" "20" "5"  "10" "20"

OMMMMM!  (Apparently "\D" means *not* a digit.)

So I have *a* solution to my problem.  However I would really like to 
know why the <expletive deleted> the first idea I tried did not work and
what it is actually *doing*!

Anybody?

cheers,

Rolf Turner

-- 
Technical Editor ANZJS
Department of Statistics
University of Auckland
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