R help - Apr 2002 - display of character NA's in a dataframe in 1.5.0

I understand that NA's in character vectors are displayed differently than
NA's
in factor vectors.
> c("x", NA, "y")
[1] "x" NA  "y"
> as.factor(c("x", NA, "y"))
[1] x    <NA> y   
Levels:  x y 

That seems sensible enough. But shouldn't I see the same behavior in a
dataframe?
> test <- data.frame(a = c("x", NA, "y"))
> test
     a
1    x
2   <NA>
3    y
> is.factor(test$a)
[1] TRUE
> is.character(test$a)
[1] FALSE

This behavior is correct since R coerces `a' to be a factor as it constructs
the test dataframe. But consider what happens when I force `a' to be
character:
> test$a <- as.character(test$a)
> is.factor(test$a)
[1] FALSE
> is.character(test$a)
[1] TRUE
> test
     a
1    x
2   <NA>
3    y

The display is the same. I would have expected it to be something like:
> test
     a
1    x
2   NA
3    y

If this is a bug, please let me know and I would be happy to submit it as
such. But, I suspect that it is more likely that there is something that I
don't fully understand about NA's and dataframes.

> R.version
         _                   
platform sparc-sun-solaris2.6
arch     sparc               
os       solaris2.6          
system   sparc, solaris2.6   
status                       
major    1                   
minor    5.0                 
year     2002                
month    04                  
day      29                  
language R                   

Thanks,

Dave Kane
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This is not a bug, and it is described in the section on USER-VISIBLE
CHANGES in the NEWS file!

Hint: consider the setting of the quote argument when printing.


On Tue, 30 Apr 2002, David Kane  <David Kane wrote:
> I understand that NA's in character vectors are displayed differently
than NA's
> in factor vectors.
>
> > c("x", NA, "y")
> [1] "x" NA  "y"
> > as.factor(c("x", NA, "y"))
> [1] x    <NA> y
> Levels:  x y
>
> That seems sensible enough. But shouldn't I see the same behavior in a
dataframe?
>
> > test <- data.frame(a = c("x", NA, "y"))
> > test
>      a
> 1    x
> 2   <NA>
> 3    y
> > is.factor(test$a)
> [1] TRUE
> > is.character(test$a)
> [1] FALSE
>
> This behavior is correct since R coerces `a' to be a factor as it
constructs
> the test dataframe. But consider what happens when I force `a' to be
character:
>
> > test$a <- as.character(test$a)
> > is.factor(test$a)
> [1] FALSE
> > is.character(test$a)
> [1] TRUE
> > test
>      a
> 1    x
> 2   <NA>
> 3    y
>
> The display is the same. I would have expected it to be something like:
>
> > test
>      a
> 1    x
> 2   NA
> 3    y
But then you would have though NA meant Nabisco.
>
> If this is a bug, please let me know and I would be happy to submit it as
> such. But, I suspect that it is more likely that there is something that I
> don't fully understand about NA's and dataframes.
>
>
> > R.version
>          _
> platform sparc-sun-solaris2.6
> arch     sparc
> os       solaris2.6
> system   sparc, solaris2.6
> status
> major    1
> minor    5.0
> year     2002
> month    04
> day      29
> language R
>
> Thanks,
>
> Dave Kane
>
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !)  To: r-help-request at
stat.math.ethz.ch
>
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>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595


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Thanks to Douglas Bates, Brian Ripley and Don MacQueen for taking the time to
answer my question. I think that Doug Bates puts it best when he writes:
>The difference in the display of character NA's is according to
>whether the quote option is on.  By default it is on for character
>vectors, so an NA is displayed as NA and the character string "NA"
is
>displayed as "NA", and off for data frames, so an NA is displayed
as
><NA> and the character string "NA" is displayed as NA.
So, in my example, we can see:
> c("x", NA, "y")
[1] "x" NA  "y"
> print(c("x", NA, "y"), quote = FALSE)
[1] x    <NA> y   
> data.frame(a = c("x", NA, "y"))
     a
1    x
2   <NA>
3    y
> print(data.frame(a = c("x", NA, "y")), quote = TRUE)
    a
1 "x"
2  NA
3 "y"

As best I can tell, this is not an "option," in the sense of something
that the
user can set with options(). That is, unless you want to override the default
print methods, the display will be different for vectors and for
dataframes. There was also information about this in the NEWS file for 1.5.0.

Thanks to all,

Dave Kane
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r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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