[R] Factors as labels in text() and mtext()
john.maindonald at anu.edu.au
Sat Jun 16 05:24:00 CEST 2001
Currently text() and mtext() give the integer levels in
such contexts as the following:
> f <- factor(letters[1:4])
> plot(1:4, 1:4, type="n")
> text(1:4, 1:4, f)
I presume this was for reasons of S-PLUS compatibility.
However one has
 "a" "b" "c" "d"
where S-PLUS2000 gives "1" in place of "a", etc.
Note that in both dialects, a test for the level
value a is f=="a", not f=="1".
The text() behaviour seems anomalous, especially if one
is serious about the statement in the draft R language
definition manual (1.2.3) that
"Factors are currently implemented using an integer
array to specify the actual levels and a second array
of names that are mapped to the integers. Rather
unfortunately users often make use of the implementation
in order to make some calculations easier. This . . .
is not guaranteed to hold in all implementations of R."
I presume that the reference is to the use of integers
for the "actual" levels. Does it imply that sometime
somewhere text(1:4, 1:4, f) might place characters
other than 1, 2, 3, 4 on the graph? Or is the current
behaviour of text() and mtext() likely to change in the
John Maindonald email : john.maindonald at anu.edu.au
Statistical Consulting Unit, phone : (6125)3998
c/o CMA, SMS, fax : (6125)5549
John Dedman Mathematical Sciences Building
Australian National University
Canberra ACT 0200
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