Mirror of forum.nim-lang.org

9798 :: Delete items in a seq while iterating over it?

• elcritch (orginal) [2023-01-05T05:12:27+01:00] view original

  A number of times I've wanted to iterate through a sequence and delete various items in it.

  However, that causes errors. I'm curious if there is an idiomatic Nim way to do it? I'm sorta hoping there's a nice tool in system.nim?

---

• moigagoo (orginal) [2023-01-05T05:52:51+01:00] view original

  If your goal is to filter out elements based on some criteria, I'd say the idiomatic way tondi that would be to use filter/filterIt or keepIf/keepItIf procs from std/sequtils.

---

• ElegantBeef (orginal) [2023-01-05T06:09:03+01:00] view original

  I generally just do the normal iterate countDown(mySeq.high, 0) and either del or delete depending if order matters. It's simple but it works :D

---

• pietroppeter (orginal) [2023-01-05T10:40:52+01:00] view original

  TIL del vs delete: https://forum.nim-lang.org/t/7928

---

• doofenstein (orginal) [2023-01-05T10:46:06+01:00] view original

  what I usually do is something like this:

  var i  = 0
  while i < myseq.len:
    if deleteCond:
      myseq.del i
    else:
      i += 1
  Run

  it also works with both delete and del, but is admitedly not that pretty.

---

• Zoom (orginal) [2023-01-05T11:12:20+01:00] view original

  It's probably best to iterate in reverse and use del, this way you don't need to double check the condition on the same index after the swap.

  ## Retains elements of a sequence specified by the predicate.
  ## Does not preserve order!
  proc retain[T](s: var seq[T]; pred: proc(x: T): bool {.closure.}) =
    for i in countDown(s.len-1, 0):
      if not pred(s[i]): s.del(i)
  
  var a = @[10, 11, 12, 13, 14]
  a.retain(proc(x: int): bool = (x mod 2 == 0))
  echo a
  Run

---

• Araq (orginal) [2023-01-05T13:53:29+01:00] view original

  I always use @doofenstein's solution.

---