Às 09:08 de 21/04/2024, Rui Barradas escreveu:
Às 08:55 de 21/04/2024, Hans W escreveu:
As we all know, in R indices for vectors start with 1, i.e, x[0] is not a
correct expression. Some algorithms, e.g. in graph theory or
combinatorics,
are much easier to formulate and code if 0 is an allowed index
pointing to
the first element of the vector.
Some programming languages, for instance Julia (where the index for
normal
vectors also starts with 1), provide libraries/packages that allow the
user
to define an index range for its vectors, say 0:9 or 10:20 or even
negative
indices.
Of course, this notation would only be feasible for certain specially
defined vectors. Is there a library that provides this functionality?
Or is there a simple trick to do this in R? The expression 'x[0]' must
be possible, does this mean the syntax of R has to be twisted somehow?
Thanks, Hans W.
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Hello,
I find what you are asking awkward but it can be done with S3 classes.
Write an extraction method for the new class and in the use case below
it works. The method increments the ndex before calling NextMethod, the
usual extraction function.
`[.zerobased` <- function(x, i, ...) {
i <- i + 1L
NextMethod()
}
as_zerobased <- function(x) {
class(x) <- c("zerobased", class(x))
x
}
x <- 1:10
y <- as_zerobased(x)
y[0]
#> [1] 1
y[1]
#> [1] 2
y[9]
#> [1] 10
y[10]
#> [1] NA
Hope this helps,
Rui Barradas
Sorry, forgot to also define a `[[zerobased` method. It's probably safer.
`[[.zerobased` <- function(x, i, ...) {
i <- i + 1L
NextMethod()
}
Hope this helps,
Rui Barradas
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