[R] Regexp: extract first occurrence of date in string

[Gabor Grothendieck]

Use regexpr to get the offset into the string and its length and then
use substr to pick extract it.

On Sat, Jan 2, 2010 at 10:43 AM, johannes rara <johannesraja at gmail.com> wrote:
> Thanks, is the same possible using basic gsub/sub/grep etc. functions?
>
> -J
>
> 2010/1/2 Gabor Grothendieck <ggrothendieck at gmail.com>:
>> Try this which uses a slightly simpler regexp:
>>
>>> library(gsubfn)
>>> strapply(txt, "(\\d{1,2}\\.\\d{1,2}\\.\\d{4}).*")[[1]]
>> [1] "05.12.2009"
>>
>> or we could convert it to Date class at the same time where we have
>> assumed month.day.year:
>>
>>> strapply(txt, "(\\d{1,2}\\.\\d{1,2}\\.\\d{4}).*", ~ as.Date(x, "%m.%d.%Y"))[[1]]
>> [1] "2009-05-12"
>>
>> or this even simpler regexp extracting all the dates and then picking
>> off the first:
>>
>>> strapply(txt, "\\d{1,2}\\.\\d{1,2}\\.\\d{4}")[[1]][1]
>> [1] "05.12.2009"
>>
>> On Sat, Jan 2, 2010 at 10:08 AM, johannes rara <johannesraja at gmail.com> wrote:
>>> I would like to extract first date from a string:
>>>
>>>> txt <- "first date is 05.12.2009. Second date is 06.12.2009."
>>>> txt
>>> [1] "first date is 05.12.2009. Second date is 06.12.2009."
>>>
>>> I tried:
>>>
>>>> sub("^.*?\\s(\\d{1,2}\\.\\d{1,2}\\.\\d{4})", "\\1", txt, extended=T, perl=T)
>>> [1] "05.12.2009. Second date is 06.12.2009."
>>>>
>>>
>>> How to modify this?
>>>
>>> -J
>>>
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>>
>