[R] Extracting day of month from Date objects ... was Re: grep pattern

[David Winsemius]

On May 24, 2011, at 10:19 AM, Kang Min wrote:

> I have another question -
>
> I'd like to extract dates from a vector of yyyy-mm-dd, so I just want
> the dd.
>
> x <- round(runif(10)*100000, digits=0)
> y <- as.Date(x, origin="1970-01-01")
>
> I tried this based on the code that Jim provided, but it just printed
> the whole date. I think I just need to tweak it a little, but haven't
> been able to figure it out.

Dates are stored as integers. You need to educate yourself about the  
differences between the internal and printed representations of R  
objects, starting with Dates and datatimes. but also including factors.

You also need to familiarize yourself with coercion functions such as  
as.character and as.numeric.
>
> y[grep("[[:digit:]]{2}$", y)]    # ????????


One of these would be more in keeping with what you asked for above
 > substr(as.character(y), 9,10)
  [1] "27" "24" "11" "14" "17" "05" "07" "16" "02" "12"
 > format(y, "%d"
+ )
  [1] "27" "24" "11" "14" "17" "05" "07" "16" "02" "12"


And please don't persist in appending questions to this thread. It's  
no longer about grep.

-- 
David.
>
> Thanks.
> Kang Min
>
> On May 23, 7:22 am, jim holtman <jholt... at gmail.com> wrote:
>> If you want to only match names of length 6, you will have to use  
>> thispattern:
>>
>>> x <- c("ZFHSJK", "ZFHJKZ","ZIOPWE","ZLKJSD","ZKFLPZ", "ZAAAAAAZ",  
>>> "ZAZ",
>>
>> +     "ZAAAAZAZ", "ZRITEZ")
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>> # match exactly values of length 6
>>> len6 <- "^Z[[:alpha:]]{4}Z$"
>>> grep(len6, x)
>> [1] 2 5 9
>>
>> On Sun, May 22, 2011 at 5:10 PM, Kang Min <ngokang... at gmail.com>  
>> wrote:
>>> Thanks!
>>
>>> On May 21, 7:09 am, David Winsemius <dwinsem... at comcast.net> wrote:
>>>> On May 20, 2011, at 11:57 AM, Kang Min wrote:
>>
>>>>> Hi all,
>>
>>>>> I'm trying to subset apatternin a vector. Each argument has 6
>>>>> letters, and I need those that start with Z and end with Z.
>>
>>>>> e.g.
>>>>> x <- c("ZFHSJK", "ZFHJKZ","ZIOPWE","ZLKJSD","ZKFLPZ")
>>
>>>>> I've looked up other discussions but still can't seem to find the
>>>>> answer.
>>
>>>> You may need to study the regex page a bit longer
>>
>>>> the "^" is the beginning of a string
>>>> ".+" will math can arbitrarily long string of anything
>>>> and "$" indicates the end of a string
>>
>>>>  > x <- c("ZFHSJK", "ZFHJKZ","ZIOPWE","ZLKJSD","ZKFLPZ")
>>>>  >grep("^Z.+Z$", x)
>>>> [1] 2 5
>>>>  >grep("^Z.+Z$", x, value=TRUE)
>>>> [1] "ZFHJKZ" "ZKFLPZ"
>>
>>>>> Thanks.
>>>>> Kangmin
>>
>>>>> ______________________________________________
>>>>> R-h... at r-project.org mailing list
>>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>>> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
>>>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>>> David Winsemius, MD
>>>> West Hartford, CT
>>
>>>> ______________________________________________
>>>> R-h... at r-project.org mailing listhttps://stat.ethz.ch/mailman/ 
>>>> listinfo/r-help
>>>> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>
>>> ______________________________________________
>>> R-h... at r-project.org mailing list
>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>> --
>> Jim Holtman
>> Data Munger Guru
>>
>> What is the problem that you are trying to solve?
>>
>> ______________________________________________
>> R-h... at r-project.org mailing listhttps://stat.ethz.ch/mailman/ 
>> listinfo/r-help
>> PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT