R help - Dec 2002 - Variance of a single number

Just out of curiosity, can some please explain the following return NA.

x <- 6
var(x)

y <- c( NA, NA, 10000 )
var(y, na.rm=T)


Unless I am seriously misguided, I believe that the variance of a single
number (i.e. a constant) should be zero. Thanks.

Regards, Adai.

Most probably:


     The denominator n - 1 is used which gives an unbiased 
estimator of
     the (co)variance for i.i.d. observations. These functions return
     `NA' when there is only one observation (whereas S-plus has 
been
     returning `NaN'), and from R 1.2.3 fail if `x' has length zero.

from help page for var

try
?var


On 10 Dec 2002 at 15:50, Adaikalavan Ramasamy wrote:
> Just out of curiosity, can some please explain the following return
> NA.
> 
> x <- 6
> var(x)
> 
> y <- c( NA, NA, 10000 )
> var(y, na.rm=T)
> 
> 
> Unless I am seriously misguided, I believe that the variance of a
> single number (i.e. a constant) should be zero. Thanks.
> 
> Regards, Adai.
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-help
Petr Pikal
petr.pikal at precheza.cz
p.pik at volny.cz

On Tue, 10 Dec 2002, Adaikalavan Ramasamy wrote:
> Just out of curiosity, can some please explain the following return NA.
>
> x <- 6
> var(x)
>
> y <- c( NA, NA, 10000 )
> var(y, na.rm=T)
>
>
> Unless I am seriously misguided, I believe that the variance of a single
> number (i.e. a constant) should be zero. Thanks.
You are.  It's an estimate of the population variance, about which there
is no information at all in one number.  Or just look at the formula,
which gives 0/0.