regular expression help

ixfd64 · 2009-03-01, 02:21

I'm having a bit of trouble with regular expressions in R.

I know the following regular expression

Code:

'^.*([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).*$'

is supposed to return e-mail addresses using backreferences.

However,

Quote:

emailpat = '^.*([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).*$'
gsub(emailpat, '\\1', 'adadasd>aaaaaaabbbbbbb@cccc.com<test')

returns

Quote:

[1] "b@cccc.com"

and cuts off the first part of the e-mail except for the first letter. Does anyone know what I'm doing wrong?

Thanks.

wblipp · 2009-03-01, 03:33

I've run into different definitions of regular expressions from time to time. But assuming your situation is like described here:

http://www.regular-expressions.info/reference.html

your problem is the the first ".*" is greedy, trying the longest possible matches first. I think you need to make it lazy, changing the .* to .*?

Code:

emailpat = '^.*?([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).*$'

If your environment doesn't support lazy, then I'd suggest a "not a regular character" before the "one or more regular characters and outside the parenthesis. so

Code:

emailpat = '^.*[^-A-Za-z0-9_.%]([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).*$'

good luck

William

ixfd64 · 2009-03-01, 06:19

The first one didn't work but the second did. Thanks so much!

2009-03-01, 03:33	#2
wblipp "William" May 2003 Near Grandkid 4505₈ Posts	I've run into different definitions of regular expressions from time to time. But assuming your situation is like described here: http://www.regular-expressions.info/reference.html your problem is the the first "." is greedy, trying the longest possible matches first. I think you need to make it lazy, changing the . to .? Code: emailpat = '^.?([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).$' If your environment doesn't support lazy, then I'd suggest a "not a regular character" before the "one or more regular characters and outside the parenthesis. so Code: emailpat = '^.[^-A-Za-z0-9_.%]([-A-Za-z0-9_.%]+@[-A-Za-z0-9_.%]+\\.[A-Za-z]+).*$' good luck William

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2009-03-01, 06:19	#3
ixfd64 Bemusing Prompter "Danny" Dec 2002 California 5·499 Posts	The first one didn't work but the second did. Thanks so much!