11 comments

• 

  David Stone

  2 years ago

  I'd tend to say that using the Array.filter method would be a cleaner way of doing it...but filter doesn't change the actual array, so you couldn't use that.
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• 

  Paul Watson

  2 years ago

  hhmm didn't know about Array.filter. Seems quite nice, though I wonder about performance?
  
  And I reckon it could be used, just use this = this.filter(func);.
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• 

  David Stone

  2 years ago

  You'd think...but setting this = this.filter... actually results in an error because you're not allowed to re-assign to this.
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• 

  Paul Watson

  2 years ago

  Ah yeah, damn, invalid assignment. Hmmmm... So it can be used outside of a prototype extension but not inside. Grr.
  
  Maybe you could do this.clear and then this.push(this.filter blah blah
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• 

  David Stone

  2 years ago

  But is that really better than the iteration and the splice?
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• 

  David Stone

  2 years ago

  Here. This:
  
  Array.prototype.remove = function(item_to_remove)
  {
  var index;
  while((index = this.indexOf(item_to_remove)) != -1)
  {
  this.splice(index, 1);
  }
  }
  
  That'll remove all of the items that match. For instance:
  
  var filtered = [1, 2, 3, 4, 5, 6, 5, 7, 8, 5, 9, 10];
  filtered.remove(5);
  document.write(filtered);
  
  1,2,3,4,6,7,8,9,10
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• 

  David Stone

  2 years ago

  Better:
  
  Array.prototype.remove = function(item_to_remove)
  {
  var index;
  while((index = this.indexOf(item_to_remove)) != -1)
  {
  this.splice(index, 1);
  }
  return this;
  }
  
  That way you can do:
  
  var filtered = [1, 2, 3, 4, 5, 6, 5, 7, 8, 5, 9, 10].remove(5);
  document.write(filtered);
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• 

  Andrew Peace

  2 years ago

  The filter operation is quite cool - Python has something identical.
  
  I'm not sure if javascript also has them, but a couple of other useful Python functions on sequences are map and reduce, which behave like:
  
  
  def map(fn, list):
  newlist = []
  for item in list:
  newlist.append = fn(item)
  
  def reduce(fn ,list, initial_arg = None):
  if initial_arg:
  val = initial_arg
  start = 0
  else:
  val = list[0]
  start = 1
  
  for i in range(start, len(list)):
  val = fn(val, myseq[i])
  return val
  
  
  I may have goofed these up as I did them off the top of my head, but hopefully you get the idea.
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• 

  Andrew Peace

  2 years ago

  Eek, that didn't look so good - not sure how to get in this message board.
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• 

  David Stone

  2 years ago

  Andrew: Here's the JS Array Object documentation that lists what functions Array does have. As you can see, map is in there. And I think reduce is kinda like every: http://developer.mozilla.org/en/docs/Core_JavaS...
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• 

  Paul Watson

  2 years ago

  And if it doesn't have it, prototype it :)
  reply