Oops.
The message in the 'stop' should be something more like "numeric index out of range".
-- Tony Plate
Tony Plate wrote:
One way could be to make a special class with an indexing method that checks for out-of-bounds numeric indices. Here's an example for vectors:
> setOldClass(c("oobcvec"))
> x <- 1:3
> class(x) <- "oobcvec"
> x
[1] 1 2 3
attr(,"class")
[1] "oobcvec"
> "[.oobcvec" <- function(x, ..., drop=T) {
+ if (!missing(..1) && is.numeric(..1) && any(is.na(..1) | ..1 < 1 | ..1 > length(x)))
+ stop("numeric vector out of range")
+ NextMethod("[")
+ }
> x[2:3]
[1] 2 3
> x[2:4]
Error in "[.oobcvec"(x, 2:4) : numeric vector out of range
>
Then, for vectors for which you want out-of-bounds checks done when they indexed, set the class to "oobcvec". This should work for simple vectors (I checked, and it works if the vectors have names).
If you want this write a method like this for indexing matrices, you can use ..1 and ..2 to refer to the i and j indices. If you want to also be able to check for missing character indices, you'll just need to add more code. Note that the above example disallows 0 and negative indices, which may or may not be what you want.
If you're extensively using other classes that you've defined, and you want out-of-bounds checking for them, then you need to integrate the checks into the subsetting methods for those classes -- you can't just use the above approach.
hope this helps,
Tony Plate
Vivek Rao wrote:
I want R to stop running a script (after printing an error message) when an array subscript larger than the length of the array is used, for example
x = c(1) print(x[2])
rather than printing NA, since trying to access such an element may indicate an error in my program. Is there a way to get this behavior in R? Explicit testing with the is.na() function everywhere does not seem like a good solution. Thanks.
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