What do tail and skip do in EK9 stream pipelines?

Tail keeps the last N elements. Skip discards the first N elements. Both are positional operations in the pipeline.

TAIL N

Keeps only the final N elements that flow through the stream:

  cat [1, 2, 3, 4, 5] | tail 2 | collect as List of Integer
  Result: [4, 5]

SKIP N

Discards the first N elements, passing the rest downstream:

  cat [1, 2, 3, 4, 5] | skip 2 | collect as List of Integer
  Result: [3, 4, 5]

COMBINED

Skip the first 2, then take only the last 2 of what remains:

  cat [1, 2, 3, 4, 5, 6] | skip 2 | tail 2 | collect as List of Integer
  Result: [5, 6]  (skip gives [3,4,5,6], tail 2 gives [5,6])

Think of skip as Unix 'tail -n +N' and tail as Unix 'tail -N'.

See Q235 for all stream operations. See Q125 for head/tail/skip. See Q896 for redirect. See Q954 for collect as custom type.

Example

defines module qa.streams.tail.skip.example

  defines program

    TailSkipDemo()
      stdout <- Stdout()

      values <- [10, 20, 30, 40, 50, 60, 70]

      //Demonstrate list operations that mirror tail and skip concepts
      stdout.println(`Full list: ${values}`)
      stdout.println(`List length: ${length values}`)

      //Access elements by index using getOrDefault
      defaultVal <- 0
      firstElement <- values.getOrDefault(0, defaultVal)
      if firstElement?
        stdout.println(`First element: ${firstElement}`)

      lastIndex <- length values - 1
      lastElement <- values.getOrDefault(lastIndex, defaultVal)
      if lastElement?
        stdout.println(`Last element: ${lastElement}`)

Other ways to ask this

How do I get the last N elements from a stream in EK9?
How do I skip elements at the start of an EK9 stream?
Can I combine tail and skip in EK9?

Coming from another language?

Java: stream().skip(n) and no direct tail — need collect then subList. Python: islice(iter, n, None) for skip, deque(iter, maxlen=n) for tail. Rust: iter().skip(n) and no direct last-n. Go: manual slicing. EK9: skip N and tail N as built-in pipeline stages.

Keywords: tail, stream, skip, pipeline, discard, positional, last