[Rd] pairlist objects

From: <hpages_at_fhcrc.org>
Date: Mon, 1 Oct 2007 19:28:29 -0700


?pairlist gives no explanation about what exactly is the difference between a pairlist and a list (except that a pairlist of length 0 is 'NULL'). So, what's a pairlist?

[1] "pairlist"

Some strange things about the "pairlist" type:

> showClass("pairlist")

  Error in getClass(Class) : "pairlist" is not a defined class

Why the above doesn't work? It works for "list":

> showClass("list")

  No Slots, prototype of class "list"

  Extends: "vector"

> is.list(.Options)

  [1] TRUE
> is.vector(.Options)

  [1] FALSE This doesn't make sense! If 'x' is a list, then it should be considered a vector too.

Subsetting a pairlist with [] doesn't produce a pairlist:

> class(.Options[1:3])

  [1] "list"

Yes, this one is documented, but still...


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