Message-ID: <77EB52C6DD32BA4D87471DCD70C8D70003B1DD94@NA-PA-VBE03.na.tibco.com>
Date: 2010-12-06T18:03:27Z
From: William Dunlap
Subject: when to use pairlist instead list
I was writing some assertion tests for modelling-related
code I had written and was surprised to see one test
fail because the "specials" attribute of the output of
terms() is a "pairlist" instead of a "list". In 2.12.0
I get:
> dput(attr(terms(y~Spec(x1)+x2, specials=c("Spec")), "specials"))
list(Spec = 2L)
> all.equal(attr(terms(y~Spec(x1)+x2, specials=c("Spec")),
"specials"), list(Spec=2L))
[1] "Modes: pairlist, list"
> all.equal(attr(terms(y~Spec(x1)+x2, specials=c("Spec")),
"specials"), pairlist(Spec=2L))
[1] TRUE
> identical(attr(terms(y~Spec(x1)+x2, specials=c("Spec")),
"specials"), pairlist(Spec=2L))
[1] TRUE
I was wondering if there was a reason for using pairlist
instead of list here or it it was just an historical
artifact. In general, when should one use pairlists?
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com