[R] methods on missing data

Thomas Lumley tlumley at u.washington.edu
Wed Jun 6 17:10:44 CEST 2001

On Wed, 6 Jun 2001 Maciej.Hoffman-Wecker at evotecoai.com wrote:

> Hello everybody!
> I have 2 >issues< concerning methods applied to missing data.
> I think they're bugs, but who knows.
> 1. var(NA) returns
>      Error in var(NA) : missing observations in cov/cor
> instead of NA. I expanded the summary-function to my.summary
> including SDev, in order to use it with tapply, which crashes
> in case of groups with no valid data.

var() already has a na.rm option that does what you want
R> var(NA,na.rm=TRUE)
[1] NA

> 2. is a similar problem. I use tapply with hist. On groups
> without valid data it crashes, like hist(as.numeric(c(NA)))
> returning
>      Error in pretty(rx, n = nnb, min.n = 1) : x must be numeric
> hist(as.numeric(c(NA)),breaks=c(1,2)) works, as it does not use "pretty".
> I know these are very special cases, but unfortunately they kill the whole
> process.

try() is a general solution to the problem of functions that must
sometimes be applied to invalid data without causing an error.  Unlike the
var(NA) case, hist(NA) can't really do anything useful so try() is a
reasonable solution.


Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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