R help - Mar 2015 - Categorizing by month

Hi everyone,

I'm trying to categorize by month in R. How can I do this if my dates are in
date/month/year form?

Thanks,
Lois



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Hi,

On Mar 27, 2015, at 12:06 PM, lychang <lychang at emory.edu> wrote:
> Hi everyone,
> 
> I'm trying to categorize by month in R. How can I do this if my dates
are in
> date/month/year form?
> 
I'm not sure about the date form you describe, but if you have the dates as
POSIXct you can extract the month as character and categorize with that.

x <- seq(from = as.POSIXct("2000/1/1",
format="%Y/%m/%d"), to = as.POSIXct("2009/12/1",
format="%Y/%m/%d"), by = 'month')
mon <- format(x, '%m')
xx <- split(x, mon)
str(xx)
List of 12
 $ 01: POSIXct[1:10], format: "2000-01-01" "2001-01-01"
"2002-01-01" "2003-01-01" ...
 $ 02: POSIXct[1:10], format: "2000-02-01" "2001-02-01"
"2002-02-01" "2003-02-01" ...
 $ 03: POSIXct[1:10], format: "2000-03-01" "2001-03-01"
"2002-03-01" "2003-03-01" ...
 $ 04: POSIXct[1:10], format: "2000-04-01" "2001-04-01"
"2002-04-01" "2003-04-01" ...
 $ 05: POSIXct[1:10], format: "2000-05-01" "2001-05-01"
"2002-05-01" "2003-05-01" ...
 $ 06: POSIXct[1:10], format: "2000-06-01" "2001-06-01"
"2002-06-01" "2003-06-01" ...
 $ 07: POSIXct[1:10], format: "2000-07-01" "2001-07-01"
"2002-07-01" "2003-07-01" ...
 $ 08: POSIXct[1:10], format: "2000-08-01" "2001-08-01"
"2002-08-01" "2003-08-01" ...
 $ 09: POSIXct[1:10], format: "2000-09-01" "2001-09-01"
"2002-09-01" "2003-09-01" ...
 $ 10: POSIXct[1:10], format: "2000-10-01" "2001-10-01"
"2002-10-01" "2003-10-01" ...
 $ 11: POSIXct[1:10], format: "2000-11-01" "2001-11-01"
"2002-11-01" "2003-11-01" ...
 $ 12: POSIXct[1:10], format: "2000-12-01" "2001-12-01"
"2002-12-01" "2003-12-01" ...

Does that help?

Ben
> Thanks,
> Lois
> 
> 
> 
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> 
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

Thanks for that Ben, I appreciate it a lot. 

I have another question if you don't mind taking the time to answer it. I
want to create a subset from dataset called "datafile5" with only the
variables "Date," "PM2.5 mean concentration,"
"SITE_LONGITUDE," and
"SITE_LATITUDE," dating only in September 2009. 

Do you know how I can do this? 



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