DISQUS

David Stone · 3 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.

Paul Watson · 3 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);.

David Stone · 3 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.

Paul Watson · 3 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

David Stone · 3 years ago

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

David Stone · 3 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

David Stone · 3 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);

Andrew Peace · 3 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.

Andrew Peace · 3 years ago

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

David Stone · 3 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...

Paul Watson · 3 years ago

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