[R] Compressing a sequence

[Steven Ellis]

Hi Dennis,

A quick Claude request:

"using r I have a sequence like:        1, 3, 4, 5, 7, 8, 12, 13, 14, 15,
20I would like to display it as:        1, 3-5, 7-8, 12-15, 20"

yielded:

condense_sequence <- function(nums) {
  if (length(nums) == 0) return("")
  if (length(nums) == 1) return(as.character(nums))

  # Sort the numbers just in case they're not in order
  nums <- sort(unique(nums))

  # Initialize variables
  ranges <- vector("character")
  start <- nums[1]
  prev <- nums[1]

  for (i in 2:length(nums)) {
    if (nums[i] != prev + 1) {
      # End of a sequence
      if (start == prev) {
        ranges <- c(ranges, as.character(start))
      } else {
        ranges <- c(ranges, paste(start, prev, sep="-"))
      }
      start <- nums[i]
    }
    prev <- nums[i]
  }

  # Handle the last number or range
  if (start == prev) {
    ranges <- c(ranges, as.character(start))
  } else {
    ranges <- c(ranges, paste(start, prev, sep="-"))
  }

  # Join all ranges with commas
  paste(ranges, collapse=", ")
}

# Your sequence
nums <- c(1, 3, 4, 5, 7, 8, 12, 13, 14, 15, 20)

# Apply the function
result <- condense_sequence(nums)
print(result)
# Output: "1, 3-5, 7-8, 12-15, 20"

Which appears to work well, though you may have other thoughts in mind /
edge cases this code does not cover.

Best,
Steven

On Fri, Feb 21, 2025 at 7:47 PM Dennis Fisher <fisher using plessthan.com> wrote:

> 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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>
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