[R] missing values

[Bill.Venables@cmis.csiro.au]

>  -----Original Message-----
> From: 	Ulrich Leopold [mailto:uleopold at science.uva.nl] 
> Sent:	Thursday, June 27, 2002 4:56 PM
> To:	r-help at stat.math.ethz.ch
> Subject:	[R] missing values
> 
> Dear list,
> 
> how can I exclude the missing values in the following example:
> 
> tapply(lsk0t50$Pox2, lsk0t50$ProfN, sum)
> 
> I tried:
> 
> tapply(lsk0t50$Pox2, lsk0t50$ProfN, sum, Fun=is.na(lsk0t50$Pox2))
	[WNV]  If you use

	tapply(thevariable, thefactor, sum, na.rm = TRUE)

	you will *almost* get what you want.

> But it returns a lot of missing values in the result. Instead the missing 
> values in the variable should not be taken into account. So that I get
> only 
> a NA as result if there are only NAs for the corresponding factor.
	[WNV]  If all values in the variable are missing and you remove them
you get an empty sum, which is 0, not NA.  So if you want this non-standard
definition of the result of an empty sum you have to say so explicitly.  One
way to do it is as follows:

	mySpecialSum <- function(x) if(all(is.na(x)) || length(x) == 0) NA
else sum(x, na.rm = TRUE)
	lapply(thevariable, thefactor, mySpecialSum)

	If you have missings in the factor (as you seem to say above) you
are in a spot of bother.

	Bill Venables. 

	  ny idea how this can be achieved?

> Thanks,
> Ulrich
> -- 
> __________________________________________________
> 
> Ulrich Leopold MSc.
> 
> Department of Physical Geography
> Institute for Biodiversity and Ecosystem Dynamics
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