avoid <<- in specific case
I agree with this. But there is (in my opinion) a much more dangerous point: a<b If there is an object called b in the function, it uses this b. But if you forgot to inialise b in the function, it looks in the global environment. So the following happens: b<<-100 a<-b (if there is no b in the function, it uses b in the global environment. So a=100 b<9 (writes to b in the local environment) Now b in the global environment is 100, while b in the function is 9 It would be more logical if a<-b would give an error if b does not exist in the function (just like pascal does). ------------------- Frans -----Oorspronkelijk bericht----- Van: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Namens Duncan Murdoch Verzonden: vrijdag 5 oktober 2012 14:26 Aan: Berry Boessenkool CC: R Help Onderwerp: Re: [R] avoid <<- in specific case
On 05/10/2012 8:19 AM, Berry Boessenkool wrote:
Hi all, I improved a function drawing horizontal histograms (code below) which
uses barplot and works fine.
It does,however, need to assign a function to the global environment to
later find the actual location on the vertical axis, and not the number of bars used by barplot.
Hopefully, running the examples below will illustrate that. As said, it works perfectly fine and does exactly what I want. The problem arises now that I'm building a package (just for myself, for now) and run into R CMD check telling me 'no visible binding for '<<-'
assignment'.
(wording below) Similar problem as in http://r.789695.n4.nabble.com/R-CMD-check-tells-me-no-visible-binding- for-global-variable-what-does-it-mean-td1837236.html My question is: Is there a way to avoid assigning the function to the global environment
with <<- but still have it available? I know it is generally not good practice. You can return the function as the value of your function. A bonus: if it is created within the body of your function, it will have access to all the local variables there. You shouldn't write to the global environment, because globalenv belongs to the user, not to you. If the user wants your function in the global environment s/he can just assign the value of your function to a variable there. Duncan Murdoch
Or ist it OK in a case like this, and is there a way to avoid the notes
from the rcmd check (make the function package-compatible)?
Or should I just ignore these notes? (I'm completely new to building packages and cannot judge the importance yet.) I'd be very thankful for any hints! Berry PS: I recently read about barcharts in lattice, but by now I'm already
used to my function. (And I learned a lot writing it a couple of years ago).
# Function horiz.hist <- function(Data, breaks="Sturges", col="transparent", las=1, ylim=range(HBreaks), labelat=pretty(ylim), labels=labelat,
border=par("fg"), ... )
{a <- hist(Data, plot=FALSE, breaks=breaks)
HBreaks <- a$breaks
HBreak1 <- a$breaks[1]
hpos <<- function(Pos) (Pos-HBreak1)*(length(HBreaks)-1)/
diff(range(HBreaks)) # Assign a function to the global environment with values calculated inside the main function.
barplot(a$counts, space=0, horiz=T, ylim=hpos(ylim), col=col,
border=border,...)
axis(2, at=hpos(labelat), labels=labels, las=las, ...)
print("use hpos() to address y-coordinates") }
# Data and basic concept
set.seed(8); ExampleData <- rnorm(50,8,5)+5
hist(ExampleData)
horiz.hist(ExampleData, xlab="absolute frequency") # Caution: the
labels at the y-axis are not the real coordinates!
# abline(h=2) will draw above the second bar, not at the label value 2.
Use hpos:
abline(h=hpos(11), col=2) # Further arguments horiz.hist(ExampleData, xlim=c(-8,20)) horiz.hist(ExampleData, main="the ... argument worked!", col.axis=3) hist(ExampleData, xlim=c(-10,40)) # with xlim horiz.hist(ExampleData, ylim=c(-10,40), border="red") # with ylim horiz.hist(ExampleData, breaks=20, col="orange") axis(2, hpos(0:10), labels=F, col=2) # another use of hpos() # One shortcoming: doesn't work with breakpoints provided as a vector with different widths of the bars Wording from the rcmd check when building a package: * checking R code for possible problems ... NOTE horiz.hist: no visible binding for '<<-' assignment to 'hpos' horiz.hist: no visible global function definition for 'hpos' [[alternative HTML version deleted]]
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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.