[R] alist()

[gah5 at comcast.net]

Peter Dalgaard <p.dalgaard at biostat.ku.dk> wrote:

> > > > x["two"] <- list(NULL)

> > This seems to work. 

> > In the actual case, it is assigning from a variable that may 
> > or may not be null, 
> > for example:

> > two<-NULL
> > x["two"]<-list(two)

> > It seems to work, and not do what it looks like, add a list of
> > length one.   I suppose I should realize by now that scalars
> > are just like lists of length one, but this still wasn't obvious.

> Actually, it is a bit more subtle:

> The key point is that the left hand side of the assignment is a list.
> This is the difference between indexing with [] rather than [[]] or $. 

Well, that and the list() on the right:

Yes, it is subtle.  I tried it out with:

x<-list()
two<-2
 x["two"]<-list(two)
typeof(x$two)

and it comes out "double", not "list"

Even more interesting:

x["two"]<-list(two,two)

Warning message:
number of items to replace is not a multiple of replacement length

Instead of a two element list in x["two"] like I might have thought.

x[["two"]]<-list(two,two)

does generate the list of list form, though.

thanks,

-- glen