indexing question
There are real examples; they are all fairly obscure. It can't be a big problem because the standard formal argument name for a data frame in modelling and graphics functions is 'data'. That's actually a more serious problem than the function called data() -- having local and global variables with the same name won't confuse R, but it can easily confuse you.
Possibilities for R getting confused include
1. The functions for environment access by name, eg exists(), get(), don't by default check the type of the argument.
2. bquote() and substitute() substitute before evaluating and could get confused.
There used to be real problems in S when certain function names were used as data names. Then there was a period of aversive conditioning by irritating warnings. As a result, I still avoid 'c' and 't' as variable names.
You could call your data frames 'df' -- many of the people who complain about 'data' don't realise that df() is the density function of the F distribution :)
-thomas
On Tue, 13 Jan 2009, Ista Zahn wrote:
On Tue, Jan 13, 2009 at 10:23 AM, jim holtman <jholtman at gmail.com> wrote:
How about this:
data(ToothGrowth) ls()
[1] "ToothGrowth"
data <- function(x){invisible(NULL)}
data(ToothGrowth)
ls()
[1] "data"
Yep, that sure does cause a problem alright. Is it the case that that problems arise when you name a function with the same name as an existing function? Or are there cases where naming data.frames, vectors, matrices, etc. can also cause problems? I hope I'm not being annoying -- I'm just trying to determine if I need to break my habit of naming data.frames "data". Thanks, Ista
On Tue, Jan 13, 2009 at 9:53 AM, Ista Zahn <istazahn at gmail.com> wrote:
From: baptiste auguie <ba208 at exeter.ac.uk> To: Dimitris Rizopoulos <d.rizopoulos at erasmusmc.nl> Date: Tue, 13 Jan 2009 09:38:09 +0000 Subject: Re: [R] indexing question
you can also look at subset,
my.data.frame <- data.frame(a=rnorm(10),
b=factor(sample(letters[1:4], 10, replace=T)))
str(my.data.frame)
my.data.frame[my.data.frame$b == "a", ]
subset(my.data.frame, b == "a")
by the way, it is probably safer not to use "data" as a variable name as
it
is also a function.
I've often wondered about this. The thing is, I've never run into a
problem
with this. For example:
ls()
character(0)
data(ToothGrowth) ls()
[1] "ToothGrowth"
rm(ToothGrowth) ls()
character(0)
data <- data.frame(1:10, 101:110) data(ToothGrowth) #works just the same ls()
[1] "data" "ToothGrowth"
In this example the data command works just the same the second time,
even
though I have a data.frame named data. Can someone give an example where
this causes a problem?
Thanks,
Ista
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______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
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