R help - May 2009 - Supplying NA or Zeros in dataframe for missing factor combinations

Hi there,
I am not getting anywhere near a solution, so here is my question. I  
have searched the archives and didn't find a solution, but maybe my  
search didn't use the right words. So here it is:

I have a dataframe with the following structure

factor1	factor2	value

In the (rather large) dataset I have to work on, there are some factor  
combinations missing, e.g.


factor1 <- c("2005", "2007", "2009)
factor2 <- c("Area1", "Area2", "Area3")

So in a perfect world there should be values for each combination in  
the dataset, eg values for "2005" in "Area1",
"Area2" and "Area3", for
"2007" and the three areas and so on.

But in my dataset some combinations are missing, e.g. a value for  
"2009" and "Area3".

How can I add complete my dataset with NA or 0 for the missing factor  
combinations?

Is there a way to use unstack or do I have to create the combinations  
first and then search for each combination within the dataframe and  
use rbind to add a row with the missing combination and a value of NA  
or 0?

Thanks,
karsten

---
Karsten D. Wolf
Universit?t Bremen
http://www.ifeb.uni-bremen.de/wolf

Tena koe Karsten

Does your dataframe contain multiple values for the same factor combination?  If
not, then using expand.grid(), followed by merge() should work.

If your dataframe is DF, then the following untested code should do it:

fullDF <- expand.grid(factor1=levels(DF$factor1), factor2=levels(DF$factor2))
fullDF <- merge(fullDF, DF, all.x=T)

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Karsten Wolf
> Sent: Friday, 15 May 2009 9:29 a.m.
> To: r-help at r-project.org
> Subject: [R] Supplying NA or Zeros in dataframe for missing 
> factorcombinations
> 
> Hi there,
> I am not getting anywhere near a solution, so here is my 
> question. I have searched the archives and didn't find a 
> solution, but maybe my search didn't use the right words. So 
> here it is:
> 
> I have a dataframe with the following structure
> 
> factor1	factor2	value
> 
> In the (rather large) dataset I have to work on, there are 
> some factor combinations missing, e.g.
> 
> 
> factor1 <- c("2005", "2007", "2009)
> factor2 <- c("Area1", "Area2", "Area3")
> 
> So in a perfect world there should be values for each 
> combination in the dataset, eg values for "2005" in
"Area1",
> "Area2" and "Area3", for "2007" and the three
areas and so on.
> 
> But in my dataset some combinations are missing, e.g. a value 
> for "2009" and "Area3".
> 
> How can I add complete my dataset with NA or 0 for the 
> missing factor combinations?
> 
> Is there a way to use unstack or do I have to create the 
> combinations first and then search for each combination 
> within the dataframe and use rbind to add a row with the 
> missing combination and a value of NA or 0?
> 
> Thanks,
> karsten
> 
> ---
> Karsten D. Wolf
> Universit?t Bremen
> http://www.ifeb.uni-bremen.de/wolf
> 
> ______________________________________________
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> 
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