[R] losing variable attributes when subsetting model.frame

[Vito Muggeo]

dear Duncan,
Thank you very much for your quick reply. Very useful and also very 
elegant, I would add.

Thanks again,
kind regards,

Vito


Il 08/05/2024 14:06, Duncan Murdoch ha scritto:
> I would guess that subsetting uses [] indexing on each column, with a 
> logical argument.  If that is true, then one solution (which is less 
> direct, but maybe someone would call it elegant) is to put a class on 
> the result of `f()`, and define a `[` method for that class that 
> preserves the attributes you want to preserve.
> 
> In your example:
> 
> f <- function(x) {
>    attr(x, "vi") <- length(x)
>    class(x) <- c("withAttributes", class(x))
>    x
> }
> 
> `[.withAttributes` <- function(x, i) {
>    subset <- NextMethod()
>    attr(subset, "vi") <- attr(x, "vi")
>    subset
> }
> 
> 
> x<- 1:5
> z<-runif(5)
> y<-rnorm(5)
> 
> mf <- model.frame(y~f(z), subset=x>=3)
> attr(mf[,2],"vi") #it works
> #> [1] 5

-- 
=================================================
Vito M.R. Muggeo, PhD
Professor of Statistics
Dip.to Sc Econom, Az e Statistiche
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