On Jun 8, 2009, at 5:27 PM, Barry Rowlingson wrote:
On Mon, Jun 8, 2009 at 10:40 PM, Tan, Richard<r...@panagora.com>
wrote:
Hi,
This is not exactly an R question but I am trying to use gsub to
replace
a string that contains 5-9 alpha-numeric characters, at least one of
which is a number. Is there a good way to write it in a one line
regex?
The only way I can think of is to spell out all the possible
expressions, somethinglike:
[0-9][a-z0-9]{4} | [a-z0-9][0-9][a-z0-9]{3} |
[a-z0-9]{2}[0-9][a-z0-9]{2} .... and so on. That is, have a regex
component for every possible 5, 6, 7, 8, and 9 character expression
with [0-9] in each place. I'm not sure this qualifies as 'good',
though..
Better to do it in two stages, one to check for 5-9 alphanumerics,
and then another to check for a number.
Here's something on a test vector 's':
cbind(s,grepl("^[A-Z0-9]{5,9}$",s),grepl("[0-9]",s))
s
[1,] "SHRT" "FALSE" "FALSE"
[2,] "5HRT" "FALSE" "TRUE"
[3,] "M1TCH" "TRUE" "TRUE"
[4,] "M1TCH5" "TRUE" "TRUE"
[5,] "LONG3RS" "TRUE" "TRUE"
[6,] "NONUMBER" "TRUE" "FALSE"
[7,] "TOOLOOOONGG" "FALSE" "FALSE"
The ones you want give two TRUE values. Extending to lower-case is
left as an exercise...
Barry
I was trying to think of a way to do this with only a single grep(),
but it has been too long of a day.
So here is a bit of a simplification on the two stage approach:
> vec
[1] "SHRT" "5HRT" "M1TCH" "M1TCH5"
"LONG3RS" "NONUMBER" "TOOLOOOONGG"
> grep("[0-9]", vec[grep("^[[:alnum:]]{5,9}$", vec)], value = TRUE)
[1] "M1TCH" "M1TCH5" "LONG3RS"
HTH,
Marc Schwartz
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