[juki]

There are shorter options in Nim too, depending on your stylistic preferences

    let sorted = entries.sorted(proc (a, b: Entry): int = cmp(a.timestamp, b.timestamp))
    let sorted = entries.sorted((a, b) => cmp(a.timestamp, b.timestamp))
    let sorted = entries.sortedByIt(it.timestamp)

I suppose you could change the whole proc to something like

    proc groupIntoThreads(entries: seq[Entry], threshold: int): seq[seq[Entry]] =
      let sorted = entries.sortedByIt(it.timestamp)

      for i, entry in sorted:
        if i == 0 or entry.timestamp - sorted[i - 1].timestamp > threshold:
          result.add(@[sorted[i]])
        else:
          result[^1].add(sorted[i])