[R] Selecting 1st and last dates from a set of dates

[Mehta, Gaurang]

Hi Jeff,
I would say my problem is what you described in 2 below. My data is as follows:
Date	UC11	UC12	UC13
02/01/1997	1	2	0
03/01/1997	5	6	3
06/01/1997	5	4	6
07/01/1997	6	4	3
08/01/1997	6	5	5
09/01/1997	7	6	8
10/01/1997	8	5	5
13/01/1997	8	6	5
14/01/1997	7	4	4
15/01/1997	6	3	3
16/01/1997	8	5	5
17/01/1997	6	4	3
20/01/1997	5	4	2
21/01/1997	7	5	5
22/01/1997	16	12	12
23/01/1997	5	3	4
24/01/1997	5	2	2
27/01/1997	8	4	5
28/01/1997	7	5	9
29/01/1997	4	4	4
30/01/1997	4	4	6
31/01/1997	9	7	8
03/02/1997	9	6	8


I want to select the data on the first date it can be 1st , 2nd or 3rd or any and last date it can be 31st, 30th and /or29th. I don’t need time.
It would be great if you could help.
Regards,
Gaurang Mehta



-----Original Message-----
From: Jeff Newmiller [mailto:jdnewmil at dcn.davis.ca.us] 
Sent: 14 July 2016 16:03
To: Mehta, Gaurang; R-help Mailing List
Subject: Re: [R] Selecting 1st and last dates from a set of dates

I suspect the answer to your question (is there a function...) is almost certainly yes, but your question is too vague to be sure.

1) Data frames and matrices are different in important ways... it is highly unlikely that matrices would be appropriate for date data. 

2) Do you mean "select records with earliest date in each month" or "select records whose day of month is 1"? If you need to work with time of day along with date then the solution will be different than if you are working with date only.

3) Have you converted your dates to Date or POSIXct or chron already? Which? 

4) There are a lot of useful functions in base R [1][2], as well as contributed packages such as chron and lubridate.

A reproducible example [3] is the standard way to communicate what problem you actually have.  In particular, including the output of dput for a representative sample of data is a key element of that example. 

[1] ?DateTimeClasses
[2] R News 4/1 p29
[3] http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example
--
Sent from my phone. Please excuse my brevity.

On July 14, 2016 5:44:52 AM PDT, "Mehta, Gaurang" <Gaurang.Mehta at royallondon.com> wrote:
>Hi Team,
>I am struggling to select the first date and last date of the month 
>where there is data in a dataframe/matrix.
>Is there any r function that can help to easily select data on the 
>first and last day of the month from the given set of dates and values.
>Thanks for the help in advance.
>Regards,
>Gaurang
>
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