as.character and a formula

Gavin Simpson <gavin.simpson at ucl.ac.uk> writes:

Dear list,

given this formula: 

fmla <- formula(y1 ~ spp1 + spp2 + spp3 + spp5)
fmla[[3]]

spp1 + spp2 + spp3 + spp5

is this the intended behaviour of as.character:

as.character(fmla[[3]])

[1] "+"                  "spp1 + spp2 + spp3" "spp5"

Yes.

? Where does the extra "+" come from?

What extra "+" ? There are three of them in fmla[[3]] and three in
as.character(....).

as.character of an object of mode call is obtained by converting it to
a list and deparsing each term (modulo some details regarding
backquotes). This is somewhat peculiar, but quite a bit of legacy code
is depending on it. Things like testing for as.character(e)[1] == "~"

O__  ---- Peter Dalgaard             ??ster Farimagsgade 5, Entr.B
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