There is, however, an important distinction.
Quoting from ?TRUE (or ?logical):
'TRUE' and 'FALSE' are reserved words denoting logical constants
in the R language, whereas 'T' and 'F' are global variables whose
initial values set to these. All four are 'logical(1)' vectors.
TRUE <- 3
Error in TRUE <- 3 : invalid (do_set) left-hand side to assignment
In other words, the rule is
T is TRUE unless otherwise defined by the user
(ditto for F)
So this rule apparently applies to input from a file. Using
colClasses is then an example of "otherwise defined by the user."
I think it's logical (pun not particularly intended) and consistent
(though perhaps not ideal, but that's another question...)
-Don
At 5:37 PM -0500 2/28/10, Gabor Grothendieck wrote:
It is strange. Even in R itself T and F are not guaranteed to be TRUE
and FALSE.
T <- 1:3
T
[1] 1 2 3
On Sun, Feb 28, 2010 at 4:55 PM, Rolf Turner <r.tur...@auckland.ac.nz> wrote:
I had occasion recently to read in a one-line *.csv file that
looked like:
"CandidateName","NSN","Ethnicity","dob","gender"
"Smith, Mary Jane",111222333,"E","2/25/1989","F"
That "F" (for female) in the last field got transformed to
FALSE. Apparently read.csv (and hence read.table) are inferring
that if the entries of a file are all F's and T's then the
field is interpreted as logical.
If I change the file to
"CandidateName","NSN","Ethnicity","dob","gender"
"Smith, Mary Jane",111222333,"E","2/25/1989","F"
"Mingdinkler, Melvin Queue",999888777,"01/04/1942","M"
then the read functions correctly interpret the last field
as being character.
The translation of "F" into FALSE resulted in some mysterious
contretemps in further analysis, which it took me a while to
track down.
I solved the problem by putting in a colClasses argument in my
call to read.csv(). But I really think that the read functions
are being too clever by half here. If field entries are surrounded
by quotes, shouldn't they be left as character? Even if they are
all F's and T's?
Furthermore using F's and T's to represent TRUE's and FALSE's is
bad practice anyway. Since FALSE and TRUE are reserved words it
would make sense for the read function to assume that a field is
logical if it consists entirely of these words. But T's and F's
.... I don't think so.
I would argue that this behaviour should be changed. I can see no
downside to such a change.
cheers,
Rolf Turner
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--
---------------------------------
Don MacQueen
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
m...@llnl.gov
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