On 14/12/2023 11:37 a.m., Martin Morgan wrote:
In the spirit of 'advent of code', maybe it is better to exploit the features
of the particular language you've chosen? Then the use of factors seems very
relevant.
value_levels <- c("Small", "Medium", "Large")
df <- data.frame(
person = c("Alice", "Bob", "Bob", "Charlie"),
value = factor(
c("Medium", "Large", "Small", "Large"),
levels = value_levels
)
)
df[with(df, order(person, value)),]
Likely this is more efficient than the hints of your existing solution, because
it will act on vectors rather than iterating through individual elements of the
'person' and 'value' vectors.
For a more general solution, I don't think I'd follow the low-level approach
Duncan suggests (maybe see also ?Math for S3 generics), but rather define a
class (e.g., that requires vectors person and value) and implement a
corresponding `xtfrm()` method.
I'd agree, in cases where it's feasible to implement one. But there are
cases where the pairwise comparison is obvious, while the numeric
conversion isn't.
A simple one would be a list of string vectors of different lengths,
where you want to sort lexicographically.
Duncan
Have fun with the remainder of the advent!
Another Martin
From: R-help <r-help-boun...@r-project.org> on behalf of Martin Møller Skarbiniks
Pedersen <traxpla...@gmail.com>
Date: Thursday, December 14, 2023 at 6:42 AM
To: R mailing list <r-help@r-project.org>
Subject: Re: [R] Sorting based a custom sorting function
On Thu, 14 Dec 2023 at 12:02, Duncan Murdoch <murdoch.dun...@gmail.com> wrote:
class(df$value) <- "sizeclass"
`>.sizeclass` <- function(left, right) custom_sort(unclass(left),
unclass(right)) == 1
`==.sizeclass` <- function(left, right) custom_sort(unclass(left),
unclass(right)) == 0
`[.sizeclass` <- function(x, i) structure(unclass(x)[i], class="sizeclass")
df[order(df$value),]
All the "unclass()" calls are needed to avoid infinite recursion. For a
more complex kind of object where you are extracting attributes to
compare, you probably wouldn't need so many of those.
Great! Just what I need. I will create a class and overwrite > and ==.
I didn't know that order() used these exact methods.
My best solution was something like this:
quicksort <- function(arr, compare_func) {
if (length(arr) <= 1) {
return(arr)
} else {
pivot <- arr[[1]]
less <- arr[-1][compare_func(arr[-1], pivot) <= 0]
greater <- arr[-1][compare_func(arr[-1], pivot) > 0]
return(c(quicksort(less, compare_func), pivot, quicksort(greater,
compare_func)))
}
}
persons <- c("alfa", "bravo", "charlie", "delta", "echo", "foxtrot", "golf",
"hotel", "india", "juliett", "kilo", "lima", "mike", "november",
"oscar", "papa", "quebec", "romeo", "sierra", "tango", "uniform",
"victor", "whiskey", "x-ray", "yankee", "zulu")
quicksort(persons, function(left, right) {
nchar(left) - nchar(right)
})
Regards
Martin
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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