[R] Compressing a sequence

[Rui Barradas]

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
> 
> 
> 	[[alternative HTML version deleted]]
> 
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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


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