[R] Subsetting data by date

[Gabor Grothendieck]

You need to review all the items I already mentioned.  The
% codes are in ?strptime so just use those appropraite to
your format.

The R manuals,

the books listed here:
http://www.r-project.org/doc/bib/R-publications.html

and the Contributed Documentation:
http://cran.r-project.org/other-docs.html

are among the items you can use to learn R.


On Mon, Jul 21, 2008 at 10:41 AM, Williams, Robin
<robin.williams at metoffice.gov.uk> wrote:
> And following on from my original question:
> In another file I have the dates in numeric format, (ddmmyy). How could
> I extract the data between 01/05/97 and 30/09/97, etc? Do I need to
> implement some sort of loop?
>
>
> Robin Williams
> Met Office summer intern - Health Forecasting
> robin.williams at metoffice.gov.uk
> -----Original Message-----
> From: Gabor Grothendieck [mailto:ggrothendieck at gmail.com]
> Sent: Monday, July 21, 2008 3:26 PM
> To: Williams, Robin
> Cc: R-help at r-project.org
> Subject: Re: [R] Subsetting data by date
>
> Continuing on, to just get points from May to Sep
>
> mo <- as.numeric(format(time(z), "%m"))
> z.summer <- z[mo >= 5 & mo <= 9]
>
> If in your case z is multivariate rather than univariate (as it is in
> our example) then it would be:
> z.summer <- z[mo >= 5 & mo <= 9, ]
>
> On Mon, Jul 21, 2008 at 9:55 AM, Gabor Grothendieck
> <ggrothendieck at gmail.com> wrote:
>> Try this:
>>
>> Lines <- "Date,Temp
>> 1-Apr-1997,50
>> 3-Sept-2001,60"
>>
>> library(zoo)
>>
>> # function to reduce 4 char mos to 3 char convert.date <- function(x,
>> format) as.Date(sub("(-...).-", "\\1-", x), format)
>>
>> # z <- read.zoo("myfile.csv", header = TRUE, sep = ",", FUN =
>> convert.date, format = "%d-%b-%Y") z <-
>> read.zoo(textConnection(Lines), header = TRUE, sep = ",", FUN =
>> convert.date, format = "%d-%b-%Y")
>>
>> plot(z)
>>
>> If the dates are actually three letters, i.e. Sep and not Sept, then
>> you could eliminate convert.date and simplify the read.zoo line to:
>>
>> z <- read.zoo(textConnection(Lines), header = TRUE, sep = ",", format
>> = "%d-%b-%Y")
>>
>> See the zoo package documentation and its three vignettes as well as
>> ?read.zoo ?strptime and ?plot.zoo and also look at the dates article
> in R News 4/1.
>>
>>
>> On Mon, Jul 21, 2008 at 9:31 AM, Williams, Robin
>> <robin.williams at metoffice.gov.uk> wrote:
>>> Hi all,
>>>  Firstly I appologise if this question has been answered previously,
>>> however searching of the archives and the internet generally has not
>>> yielded any results.
>>>
>>>  I am looking in to the effects of summer weather conditions
>>> (temperature, humidity etc), on the incidences of a breathing
>>> disorder brought on through smoking (COPD). I am fairly new to R and
>>> completely new to the idea of writing R scripts, subsetting
>>> dataframes etc. I am working on a 12 week summer placement at the Met
>
>>> Office, UK, having just finished my second year of a mathematics
> course at university.
>>>
>>>  Basically I have data between January 1 1997 and December 31 2007.
>>> However as I am only interest in the summer months (which I have
>>> defined to be between May 1 and September 30), I would like to
>>> extract the relevant data in R in a timely manner. Obviously I could
>>> go and open my csv files in excel, cut and paste the relevant data,
>>> etc, however I would like to maximise R's potential as I feel it will
>
>>> stand me in better stead in the long run.
>>>  Currently the dates are in the form
>>> 1-Apr-1997,
>>> 3-Sept-2001,
>>> etc.
>>>  I will create a data.frame with date as one of the variables, the
>>> others being (initially) temperature, humidity, and Admissions (the
>>> number of hospital admissions for COPD exaserbations).
>>>  Please could somebody tell me if there is a simple way to extract
>>> the data I want, and if so perhaps a sample command to get me going?
>>> Do I first need to format the dates to some numeric-only format? As I
>
>>> say, I could use Excel to create the files in the right format, but I
>
>>> will be dealing with a lot more variables in the future (perhaps up
>>> to 8) and so this will become a pain-staking process.
>>>
>>>  Please reply either on or off list.
>>>
>>> Many thanks for any help.
>>> Robin Williams
>>> Met Office summer intern - Health Forecasting
>>> robin.williams at metoffice.gov.uk
>>>
>>>
>>>        [[alternative HTML version deleted]]
>>>
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>>
>