[R] using ddply but preserving some of the outside data

[Gabor Grothendieck]

In particular, try this:

> library(zoo)
> a.wide <- reshape(a.df, dir = "wide", timevar = "dates", idvar = "sites")
> rollmean(as.zoo(t(a.wide[,-1])), 2)

1 56.855685 58.62981 95.14842
2 58.049821 58.81659 78.70020
3 11.199634 89.91179 76.22853
4  1.152741 43.63333 93.03040


On Wed, Aug 5, 2009 at 3:05 PM, David Winsemius<dwinsemius at comcast.net> wrote:
>
>
> library(zoo)
> ?rollmean
>
> On Aug 5, 2009, at 3:00 PM, Jarrett Byrnes wrote:
>
>> I have a bit of a quandy.  I'm working with a data set for which I have
>> sampled sites at a variety of dates.  I want to use this data, and get a
>> running average of the sampled values for the current and previous date.
>>
>> I originally thought something like ddply would be ideal for this,
>> however, I cannot break up my data by date, and then apply a function that
>> requires information about the previous dates.
>>
>> I had thought to use a for loop and merge, but that doesn't quite seem to
>> be working.
>>
>> So, my questions are twofold
>>
>> 1) Is there a way to use something like the plyr library to do this
>> efficiently
>>        1a) Indeed, is there a way to use ddply or its ilk to have a
>> function that returns a vector of values, and then assign the variables you
>> are sorting by to the whole vector?  Or maybe making each value it's own
>> column in the new data frame, and then using reshape is the answer.  Hrm.
>>  Seems clunky.
>>
>> 2) Or, can a for loop around a plyr-kind of statement do the trick (and if
>> so, pointers on why the below code won't work) (also, it, too, seems
>> clunkier than I would like)
>>
>>
>> sites<-c("a", "b", "c")
>> dates<-1:5
>>
>> a.df<-expand.grid(sites=sites, dates=dates)
>> a.df$value<-runif(15,0,100)
>> a.df<-as.data.frame(a.df)
>>
>>
>> #now, I want to get the average of the
>> mean2<-function(df, date){
>>        sub.df<-subset(df, df$dates-date<1 &
>>                                df$dates-date>-1 )
>>        return(mean(df$value))
>>        }
>>
>> my.df<-data.frame(sites=NA, dates=NA, V1=NA)
>> for(a.date in a.df$dates){
>>        new.df<-ddply(a.df, "sites", function(df) mean2 (df, a.date))
>>        my.df<-merge(my.df, new.df) #doesn't seem to work
>> }
>>
>> my.df
>>
>> ______________________________________________
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>> 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
> Heritage Laboratories
> West Hartford, CT
>
> ______________________________________________
> 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.
>