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4966 :: Getting OrderedTable key/value pair by insertion order

• squattingmonk (orginal) [2019-06-25T02:31:22+02:00] view original

  Hi, all! I'm trying to get the first item out of an OrderedTable that was indexed with strings. I'm not sure which is the best way to do it.

  My program is reading a set of configuration files and loading the information into a type Target, which is then added to an ordered table using the name of the target as its index. If the user executes a command that takes a target, I want to get the target using the supplied name as the index (just normalized). So far, so good. However, if the user does not specify a target, I want to select the first one that was added to the table.

  Here's my types:

  type
    Config* = object
      # ...
      targets*: OrderedTable[string, Target]
    
    Target = object
      name*, file*, description*: string
      sources*: seq[string]
  Run

  This is the only way I can think of to get the first index:

  if opts.target.len == 0:
    for target in cfg.targets.keys:
      opts.target = target
      break
   
  Run

  Is there a better way of getting the first index? Or maybe a better way to structure my data that avoids this?

  Thanks!

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• Araq (orginal) [2019-06-25T13:38:43+02:00] view original

  I don't understand the question: An OrderedTable keeps the insertion order, it's not a "SortedTable" (which the stdlib still lacks)

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• Stefan_Salewski (orginal) [2019-06-25T16:19:21+02:00] view original

  From your last code sample, I think I understand that you want to retrieve the table entry, that was added first to table. So indeed iterating over the keys and stopping after first one makes sense, I think there is no function to retrieve the first added element. And I think I can remember someone asking how to get the n-th. added element, conclusion was to use a loop similar as you do.

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• squattingmonk (orginal) [2019-06-25T17:19:51+02:00] view original

  I'm not trying to get sorted items, just the first item added (hence why I used an OrderedTable).

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• lucian (orginal) [2019-06-25T18:50:33+02:00] view original

  use

  iterator pairs[A, B](t: OrderedTable[A, B]): (A, B)
  Run

  and break-out after first (does "... in insertion order." kind of implies FIFO?) element.

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• Araq (orginal) [2019-06-25T20:50:34+02:00] view original

  Ok, yeah, we have no api for that.

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• squattingmonk (orginal) [2019-06-25T23:05:36+02:00] view original

  So indeed iterating over the keys and stopping after first one makes sense, I think there is no function to retrieve the first added element. And I think I can remember someone asking how to get the n-th. added element, conclusion was to use a loop similar as you do.

  Thanks, Stefan. I'd though I was just being silly and missing something obvious. Good to know this is a reasonable solution.

  use

  iterator pairs[A, B](t: OrderedTable[A, B]): (A, B)
  Run

  and break-out after first (does "... in insertion order." kind of implies FIFO?) element.

  Hi, lucian. That's what I did in the code sample I provided, but I used the keys iterator instead of pairs.

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• mratsim (orginal) [2019-06-26T11:44:44+02:00] view original

  We're still waiting for your B-Trees implementation to have SortedTable in the standard lib ;)

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