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6914 :: Double for loops

• archnim (orginal) [2020-10-12T15:21:47+02:00] view original

  Hello world. I was trying this morning, to loop on two seqs at the same time, but in a reverse order. For example:

  var
      seq1 = @[ #[First seq's content]# ]
      seq2 = @[ #[Second seq's content]# ]
  
  for index in countdown(seq1.len, 0):
      echo (seq1[index] + seq2[index])
  Run

  But I faced an issue: The two sequences didn't have the same length. I finaly found another way to implement my algorithm. But i'm still asking myself: Isn't there any manner to do a double loop ? What about adding that to Nim ? I imagine something like this:

  var
      seq1 = @[ #[First seq's content]# ]
      seq2 = @[ #[Second seq's content]# ]
  
  for
      index1 in countdown(seq1.len, 0)
      index2 in countdown(seq2.len, 0)
  : # When the length of the shortest seq is reached, the loop stops
      echo (seq1[index1] + seq2[index2])
  Run

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• inventormatt (orginal) [2020-10-12T15:42:04+02:00] view original

  I believe what you are look for is zip which can be found in sequtils https://nim-lang.org/docs/sequtils.html . it only works for two openarrays at a time but it should do what you are asking for.

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• cblake (orginal) [2020-10-12T15:47:10+02:00] view original

  It sounds like you want a generalization of sequtils.zip (perhaps that takes a closure iterator that could go backwards like your example and metadata like expected iteration ranges). In Nim nothing stops you from just writing that and using it in your own code (or possibly generalizing it from 2 to N iter-ees). You might also be able to use for loop macros to get a syntax you find palatable.

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• Araq (orginal) [2020-10-12T15:56:49+02:00] view original

  Sometimes a tiny amount of math does the trick:

  var
      seq1 = @[ #[First seq's content]# ]
      seq2 = @[ #[Second seq's content]# ]
  
  for index in countdown(min(seq1.len, seq2.len)-1, 0):
      echo(seq1[index] + seq2[index])
  
  Run

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• pietroppeter (orginal) [2020-10-12T17:03:25+02:00] view original

  or maybe you want to loop over the tail of the sequences. here is this option compared with @araq's way in a simple example (playground):

  var
      seq1 = @[ 1, 2, 3 ]
      seq2 = @[ 1, 2, 3, 4, 5, 6 ]
  
  for index in countdown(min(seq1.len, seq2.len)-1, 0):
      echo((seq1[index], seq2[index], seq1[index] + seq2[index]))
  
  echo ""
  
  for index in 1 .. min(seq1.len, seq2.len):
      echo((seq1[^index], seq2[^index], seq1[^index] + seq2[^index]))
  Run

  output:

  
  (3, 3, 6)
  (2, 2, 4)
  (1, 1, 2)
  
  (3, 6, 9)
  (2, 5, 7)
  (1, 4, 5)
  Run

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