[R] help incorporating data subset lengths in function with ddply

Wed Apr 16 21:35:11 CEST 2014

Hi

Do you seek something like this:

mydat <- read.table(text="
storm,Q_time,Q, duration
s1,2008-08-07 21:15:00,0.000,1
s1,2008-08-07 21:16:00,3.020,2
s1,2008-08-07 21:17:00,6.041,3
s1,2008-08-07 21:18:00,9.061,4
s1,2008-08-07 21:19:00,12.082,5
s1,2008-08-07 21:20:00,15.102,6
s1,2008-08-07 21:21:00,18.123,7
s1,2008-08-07 21:22:00,11.143,8
s1,2008-08-07 21:23:00,0.000,9
s2,2010-10-05 21:00:00,0.000,1
s2,2010-10-05 21:01:00,1.812,2
s2,2010-10-05 21:02:00,3.625,3
s2,2010-10-05 21:03:00,5.437,4
s2,2010-10-05 21:04:00,7.249,5
s2,2010-10-05 21:05:00,9.061,6
s2,2010-10-05 21:06:00,0.874,7
s2,2010-10-05 21:07:00,0.000,8",
                    h = TRUE, sep =",", stringsAsFactors = FALSE)

mydat$Q_time <- as.POSIXct(strptime(mydat$Q_time, format = "%Y-%m-%d %H:%M:%S"))

tmp <- aggregate(Q_time ~ storm, data = mydat, FUN = function(x) diff(range(x)))

tmp

str(tmp)

Yours sincerely / Med venlig hilsen

Frede Aakmann Tøgersen
Specialist, M.Sc., Ph.D.
Plant Performance & Modeling

Technology & Service Solutions
T +45 9730 5135
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> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> On Behalf Of Steve E.
> Sent: 16. april 2014 21:01
> To: r-help at r-project.org
> Subject: [R] help incorporating data subset lengths in function with ddply
> 
> Dear R Community,
> 
> I am having some trouble with a task that I hope you might be able to help
> with. I have a dataset that includes the time and corresponding stream
> discharge from numerous storms (example of structure with simplified data
> below). I would like to produce a field that details the duration of each
> storm, where each storm is a subset of the data and the duration runs from
> zero to end for each unique storm. I have been trying to accomplish this
> with ddply but to no avail as I am unable to provide ddply (e.g., below)
> with the length of the storm (i.e., subset of data). Thank you in advance,
> any help would be appreciated.
> 
> 
> existing df:
> storm,Q_time,Q
> s1,2008-08-07 21:15:00,0.000
> s1,2008-08-07 21:16:00,3.020
> s1,2008-08-07 21:17:00,6.041
> s1,2008-08-07 21:18:00,9.061
> s1,2008-08-07 21:19:00,12.082
> s1,2008-08-07 21:20:00,15.102
> s1,2008-08-07 21:21:00,18.123
> s1,2008-08-07 21:22:00,11.143
> s1,2008-08-07 21:23:00,0.000
> s2,2010-10-05 21:00:00,0.000
> s2,2010-10-05 21:01:00,1.812
> s2,2010-10-05 21:02:00,3.625
> s2,2010-10-05 21:03:00,5.437
> s2,2010-10-05 21:04:00,7.249
> s2,2010-10-05 21:05:00,9.061
> s2,2010-10-05 21:06:00,0.874
> s2,2010-10-05 21:07:00,0.000
> 
> desired df:
> storm,Q_time,Q, duration
> s1,2008-08-07 21:15:00,0.000,1
> s1,2008-08-07 21:16:00,3.020,2
> s1,2008-08-07 21:17:00,6.041,3
> s1,2008-08-07 21:18:00,9.061,4
> s1,2008-08-07 21:19:00,12.082,5
> s1,2008-08-07 21:20:00,15.102,6
> s1,2008-08-07 21:21:00,18.123,7
> s1,2008-08-07 21:22:00,11.143,8
> s1,2008-08-07 21:23:00,0.000,9
> s2,2010-10-05 21:00:00,0.000,1
> s2,2010-10-05 21:01:00,1.812,2
> s2,2010-10-05 21:02:00,3.625,3
> s2,2010-10-05 21:03:00,5.437,4
> s2,2010-10-05 21:04:00,7.249,5
> s2,2010-10-05 21:05:00,9.061,6
> s2,2010-10-05 21:06:00,0.874,7
> s2,2010-10-05 21:07:00,0.000,8
> 
> I have been trying variations of the following statement, but I cannot seem
> to get the length of the subset correct as I receive an error of the type
> 'Error: arguments imply differing number of rows: 2401, 0'.
> 
> newdf <- ddply(df, "storm", transform, FUN = function(x)
> {duration=seq(from=1, by=1, length.out=nrow(x))})
> 
> I would really like to get a handle on ddply in this instance as it will be
> quite helpful for many other similar calculations that I need to do with
> this dataset.
> 
> Thanks again,
> Stevan
> 
> 
> 
> 
> --
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> incorporating-data-subset-lengths-in-function-with-ddply-tp4688926.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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