as.character and a formula

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"

? Where does the extra "+" come from?
as.character(fmla)
[1] "~"                         "y1"                       
[3] "spp1 + spp2 + spp3 + spp5"

Thanks in advance,

Gav
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Gavin Simpson                     [T] +44 (0)20 7679 5522
ENSIS Research Fellow             [F] +44 (0)20 7679 7565
ENSIS Ltd. & ECRC                 [E] gavin.simpsonATNOSPAMucl.ac.uk
UCL Department of Geography       [W] http://www.ucl.ac.uk/~ucfagls/cv/
26 Bedford Way                    [W] http://www.ucl.ac.uk/~ucfagls/
London.  WC1H 0AP.
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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"

? Where does the extra "+" come from?
Which *extra* "+"?

This expression is the same as

"+"(spp1 + spp2 + spp3, spp5)

hence "+" with arguments "spp1 + spp2 + spp3" and "spp5"

Same below.

Uwe Ligges

as.character(fmla)
[1] "~"                         "y1"                       
[3] "spp1 + spp2 + spp3 + spp5"

Thanks in advance,

Gav
I guess the problem is that Gavin is unaware of what [[]] does for a call.
It is still a call and so you want to use deparse() and not 
as.character():
deparse(fmla[[3]])
[1] "spp1 + spp2 + spp3 + spp5"

Watch out for the line length limit on deparse() if you do this in 
programs.

Gavin Simpson wrote:

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"

? Where does the extra "+" come from?
Which *extra* "+"?

This expression is the same as

"+"(spp1 + spp2 + spp3, spp5)

hence "+" with arguments "spp1 + spp2 + spp3" and "spp5"

Same below.

Uwe Ligges

as.character(fmla)
[1] "~"                         "y1"
[3] "spp1 + spp2 + spp3 + spp5"

Thanks in advance,

Gav

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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
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)                  FAX: (+45) 35327907
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.
Thanks Uwe, Brian and Peter for setting me straight. Being unobservant,
forgetful and stupid, all in one day, is some going, even for me.

All the best,

Gav
? 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] == "~"

%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%
Gavin Simpson                     [T] +44 (0)20 7679 5522
ENSIS Research Fellow             [F] +44 (0)20 7679 7565
ENSIS Ltd. & ECRC                 [E] gavin.simpsonATNOSPAMucl.ac.uk
UCL Department of Geography       [W] http://www.ucl.ac.uk/~ucfagls/cv/
26 Bedford Way                    [W] http://www.ucl.ac.uk/~ucfagls/
London.  WC1H 0AP.
%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%