[R] "NaN" answer don't understand why

[Bill Dunlap]

fit <- robustgam::robustgam(...) produces a list, with no class attached,
so residuals(fit) invokes the default method for residuals(), which
essentially returns the 'residuals' component of 'fit'.  There is no such
component so it returns NULL, an object of length zero.  The mean of a
length-zero object is NaN.

It would make sense for mean(NULL) or sum(NULL) to give an error since they
are only meant to work on numbers.  However this would probably break some
existing code, since there are various functions that return NULL instead
of numeric(0).

-Bill

On Fri, Nov 13, 2020 at 2:05 PM varin sacha via R-help <r-help using r-project.org>
wrote:

> Dear R-experts,
>
> Here below my reproducible example. No error message but I can not get a
> result. I get "NaN" as a result. I don't understand what is going on. Many
> thanks for your precious help, as usual.
>
>
>  # # # # # # # # # # # # # # # # # # # # # # # # #
>
> x<-c(499,491,500,517,438,495,501,525,516,494,500,453,479,481,505,465,477,520,520,480,477,416,502,503,497,513,492,469,504,482,502,498,463,504,495)
>
> y<-c(499,496,424,537,480,484,503,575,540,436,486,506,496,481,508,425,501,519,546,507,452,498,471,495,499,522,509,474,502,534,504,466,527,485,525)
>
> library(robustgam)
> true.family <- poisson()
>
> #Robust GAM
> fit=robustgam(x,y,sp=0,family=true.family,smooth.basis='ps',K=3)
>
> #OLS
> fit1 <- lm(y~x)
>
> #Huber-M
> library(robustbase)
> library(MASS)
> fit2=rlm(y~x)
>
> #GAM
> library(mgcv)
> fit3=gam(y~s(x))
>
> # MSE of OLS linear model
> mean(residuals(fit1)^2)
>
> # MSE of Huber-M linear model
> mean(residuals(fit2)^2)
>
> # MSE of GAM
> mean(residuals(fit3)^2)
>
> # MSE of robust GAM
> mean(residuals(fit)^2)
>  # # # # # # # # # # # # # # # # # # # # # # # # #
>
>
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