R help - Sep 2010 - Writing My Own Function to Use With aggregate

Dear R-Users,

I have been using R for about 1 week and recently learned about the Aggregate
function, and from reading online it seems like it is comparable to a SQL group
by to perform summary functions.  I am looking to do a summary function, such as
SUM/MIN, but instead of these basic functions, I would like to calculate the
IRR.

Assuming I have a data set DS01:
FirstName         LastName         NCF      Date
A                      B                      -100                  1/1/2001
A                      B                      50                     2/1/2002
A                      B                      200                   3/1/2003
A                      C                      -500                  1/1/2001
A                      C                      50                     2/1/2002
A                      C                      70                     3/1/2003
A                      C                      50                     2/1/2004
A                      C                      70                     3/1/2005

And an IRR function which takes in a cash flow and dates as inputs:
IRR(NCF,cfDate) and returns the IRR

I tried the following:
aggregate(DS01$NCF,by=list(DS01$ FirstName,DS01$ LastName),RR,cfDate=DS01$Date)

and I got the following error:
Error in aggregate.data.frame(as.data.frame(x), ...) :
  arguments must have same length

If anyone could shed some light on what may be causing this that would be great.
More importantly, is this the right way to do this (should I even be using the
aggregate function)?

Any help would be greatly appreciated!
Thanks!





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On Sep 1, 2010, at 6:29 PM, Adrian Ng wrote:
> Dear R-Users,
>
> I have been using R for about 1 week and recently learned about the  
> Aggregate function, and from reading online it seems like it is  
> comparable to a SQL group by to perform summary functions.  I am  
> looking to do a summary function, such as SUM/MIN, but instead of  
> these basic functions, I would like to calculate the IRR.
>
> Assuming I have a data set DS01:
> FirstName         LastName         NCF      Date
> A                      B                      -100                   
> 1/1/2001
> A                      B                      50                      
> 2/1/2002
> A                      B                      200                    
> 3/1/2003
> A                      C                      -500                   
> 1/1/2001
> A                      C                      50                      
> 2/1/2002
> A                      C                      70                      
> 3/1/2003
> A                      C                      50                      
> 2/1/2004
> A                      C                      70                      
> 3/1/2005
>
> And an IRR function which takes in a cash flow and dates as inputs:  
> IRR(NCF,cfDate) and returns the IRR
>
> I tried the following:
> aggregate(DS01$NCF,by=list(DS01$ FirstName,DS01$  
> LastName),RR,cfDate=DS01$Date)
Since you are not forthcoming with the code for IRR (nor did you even  
spell it correctly in your aggregate call), I will simple suggest that  
you consider using the functions from the plyr package or if you  
wanted to do it the old way you could look up split() and do :

lapply (split(DS01, list(DS01$ FirstName,DS01$ LastName), IRR(NCF,  
cfDate=Date) ).

Plyr method (perhaps):

require(plyr)
ddply(DS01, .( FirstName, LastName), function(df) IRR(NCF,  
cfDate=Date) )

I'm quite sure that the data.table functionality could handle it quite  
easily as well.

>
> and I got the following error:
> Error in aggregate.data.frame(as.data.frame(x), ...) :
>  arguments must have same length
>
> If anyone could shed some light on what may be causing this that  
> would be great.
aggregate() takes a vector while you need to pass a more complex  
structure. I think you passed the entire length of Date.

> More importantly, is this the right way to do this (should I even be  
> using the aggregate function)?
>
> Any help would be greatly appreciated!
> Thanks!
>
>
>
>
>
> Please consider the environment before printing this e-mail.
>
> 	[[alternative HTML version deleted]]
>
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David Winsemius, MD
West Hartford, CT