Hello,
Inline.
Às 18:47 de 22/02/2025, avi.e.gr...@gmail.com escreveu:
Rui,
Your post (way at the bottom) expands beyond what was requested and that makes
it more interesting.
I like to look at what I consider reusable ideas and tools.
One was the reminder of using apply across rows of a matrix which would have
applied to my earlier post of a package that also created a matrix of
sequential followed by a count.
Another was the idea of creating a changed object that now has an additional
class that can determine which new print function to use automagically. I do
wonder what happens if there are other classes that also have such a function.
Does the first class in the listing dominate?
Yes, to call the 2nd, use NextMethod().
Continues at the end.
Finally, I have been considering the broader question of how to create a more
abstract function along the lines being discussed.
This request was about integers and the definition of being next but contiguous was to be
one apart. Clearly, there can be cases where you want say just contiguous even (or odd)
numbers so that c(2, 6,8,10) becomes "2, 6-10" as in street addresses for
deliveries on one side of a street where all addresses on that side are even. That could
be handled by not hard-coding in a difference of 1, but providing a successor() function
that returns TRUE/FALSE when supplied with two arguments. One method is to allow such a
function as an argument.
A related idea would be to allow other entries where a successor has meaning. Consider c("a", "c", "d", "e",
"x", "y") which you can imagine collapsed as "a, c-e, x-y" as one example. But you can broaden it to work with
something like Roman numerals in text form. Having a successor function, as above, could allow such additional functionality.
And, of course, other options could be allowed, perhaps to just pass through,
so that you can specify the sep(arator) or col(lapse) strings such as instead
of this:
"1, 3-6, 12-19"
You might see:
1
3:6
12:19
As in multiple lines and colon separated.
But one question I keep asking is about complexity. We have seen a number of
solutions and some of them require many passes over what could be a long vector
and other data structures like matrices with quite a few passes. It is nice to
re-use bits and pieces but perhaps for longer examples, not in prototyping
mode, writing a custom function that passes minimally over the data, may be a
better choice.
-----Original Message-----
From: R-help <r-help-boun...@r-project.org> On Behalf Of Rui Barradas
Sent: Saturday, February 22, 2025 7:36 AM
To: Dennis Fisher <fis...@plessthan.com>; r-help <r-help@r-project.org>
Subject: Re: [R] Compressing a sequence
Às 00:46 de 22/02/2025, Dennis Fisher escreveu:
R 4.4.0
OS X
Colleagues
I have a sequence like:
1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 20
I would like to display it as:
1, 3-5, 7-8, 12-15, 20
Any simple ways to accomplish this?
Dennis
Dennis Fisher MD
P < (The "P Less Than" Company)
Phone / Fax: 1-866-PLessThan (1-866-753-7784)
www.PLessThan.com
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Hello,
Here is a way with package R.utils, function seqToIntervals.
x <- scan(text = "1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 20", sep = ",")
mat <- R.utils::seqToIntervals(x)
apply(mat, 1L, \(m) {
ifelse(m[1L] == m[2L], m[1L], paste(m, collapse = "-"))
})
#> [1] "1" "3-5" "7-8" "12-15" "20"
If you want to be fancy, define a special class that prints like that.
x <- scan(text = "1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 20", sep = ",")
as_seqInterval <- function(x) {
old_class <- class(x)
class(x) <- c("seqInterval", old_class)
x
}
print.seqInterval <- function(x, ...) {
mat <- R.utils::seqToIntervals(x)
out <- apply(mat, 1L, \(m) {
ifelse(m[1L] == m[2L], m[1L], paste(m, collapse = "-"))
})
print(out)
}
y <- as_seqInterval(x)
class(y)
#> [1] "seqInterval" "numeric"
# autoprinting y
y
#> [1] "1" "3-5" "7-8" "12-15" "20"
# explicit printing y
print(y)
#> [1] "1" "3-5" "7-8" "12-15" "20"
Hope this helps,
Rui Barradas
With the example from my first post, there is another advantage in using
a new class. Since this new class sub-classes "numeric" "seqInterval"
numbers can be added, subtracted, etc, they will keep the expected
behaviour of numbers.
x2 <- c(1:3, 5, 6)
length(x)
#> [1] 11
length(x2)
#> [1] 5
y2 <- as_seqInterval(x2)
y2
#> [1] "1-3" "5-6"
x + x2
#> Warning in x + x2: longer object length is not a multiple of shorter
object
#> length
#> [1] 2 5 7 10 13 9 14 16 19 21 21
# make it more obvious that 9, 10 and 13, 14 should be compressed
sort(x + x2)
#> Warning in x + x2: longer object length is not a multiple of shorter
object
#> length
#> [1] 2 5 7 9 10 13 14 16 19 21 21
# to add two objects of class "seqInterval" keeps the compressing property
as_seqInterval(x + x2)
#> Warning in x + x2: longer object length is not a multiple of shorter
object
#> length
#> [1] "2" "5" "7" "9-10" "13-14" "16" "19" "21"
y + y2
#> Warning in y + y2: longer object length is not a multiple of shorter
object
#> length
#> [1] "2" "5" "7" "9-10" "13-14" "16" "19" "21"
# now a division, the results are not integer
y/2
#> [1] "0-4" "6-7" "10"
unclass(y/2)
#> [1] 0.5 1.5 2.0 2.5 3.5 4.0 6.0 6.5 7.0 7.5 10.0
Hope this helps,
Rui Barradas
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