Smartest way to initialize an array in CoffeeScript

Question

What is the best way to initialize an array with a particular value 0 in coffee script. What I have done so far -

[0..100].map -> 0

And

arr = []
arr.push(0) while arr.length isnt 100

If personally feel that the first one will have a poor performance and the second one is too verbose and destroys the charm of programming in coffee script.

Update 2: Incase performance is not an issue then this is also an option I suppose.

arr = new Array(10).join(0).split('')

Update 2: the above will perform better than others options if the join is passed number

Update 3: After seeing a couple of JSPerf tests mentioned in the comments and answers I tried to perform them my self using node.js. Here are the weird results - Code -

    size = 10000000;
key = 1

console.time('splits')
arr1= Array(size + 1).join(key).split('')
console.timeEnd('splits')


console.time('maps')
arr2 = [1..size].map -> key
console.timeEnd('maps')

console.time('loop')
arr3 = []
arr3.push(key) while arr3.length isnt size
console.timeEnd('loop')


console.time('for')
arr4 = (0 for n in [0...size])
console.timeEnd('for')

console.time('for-no-var')
arr5 = (0 for [0...size])
console.timeEnd('for-no-var')


### node- 0.10.15
splits: 162ms
maps: 1639ms
loop: 607ms
for: 659ms
###

Interestingly the split and join is taking much less time. Also if we care about performance really then we should try to initialize and array which is really big instead of something in the order of hundreds.

Use the first it's very nice and clear. Worry about performance when it becomes an issue. — Benjamin Gruenbaum
– Benjamin Gruenbaum, Commented Aug 30, 2013 at 22:13
Yes that too. I wish there was a builtin feature for this in coffeescript. I love the way we can swap numbers in coffeescript using arrays. — tusharmath
– tusharmath, Commented Aug 31, 2013 at 0:11
jsperf.com/big-array-initialize/2 finds that push out performs ary[x]=0 on Chrome, but not on Firefox. There are many more such tests on jsperf.com — hpaulj
– hpaulj, Commented Aug 31, 2013 at 16:52
The join/split version creates ['0','0',...]. Initials to characters, not integers. — hpaulj
– hpaulj, Commented Aug 31, 2013 at 18:02

epidemian · Accepted Answer · 2013-09-01 00:02:41Z

17

There's also the arr = (0 for [1..100]) form if you don't want to have any iteration variable leaking outside the comprehension ;)

answered Sep 1, 2013 at 0:02

epidemian

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4 Comments

tusharmath Over a year ago

This is what I would go for, but its performance isn't as great as the one @nicolashruchten's answer see jsperf.com/array-initialization-in-coffeescript/4

nicolaskruchten Over a year ago

This answer is better than mine, and it compiles to essentially exactly the same JS minus the variable, so the performance should very very close

epidemian Over a year ago

@Tushar, notice that in that jsPerf the size of the array is not hard-coded in the expression (it uses (0 for [0...size]) instead of (0 for [0...100000])), and because of that, the Coffee compiler generates a loop that has to check if the range is ascending or descending in each iteration. Nevertheless, Firefox doesn't seem to suffer any performance penalty because of that :D

tusharmath Over a year ago

This seems like the best option interms of both performance and syntax. Thanks :)

nicolaskruchten · Accepted Answer · 2013-08-31 22:03:59Z

5

My vote goes to arr = (0 for x in [0...100])

It's clear, concise, CoffeeScript-ish, and compiles to reasonably clear Javascript:

var arr, x;

arr = (function() {
  var _i, _results;
  _results = [];
  for (x = _i = 0; _i < 100; x = ++_i) {
    _results.push(0);
  }
  return _results;
})();

answered Aug 31, 2013 at 22:03

nicolaskruchten

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2 Comments

tusharmath Over a year ago

Can we get rid of the variable x in CoffeeScript?

tusharmath Over a year ago

@epidemian has given an example for it.

Ben McCormick · Accepted Answer · 2013-08-31 20:57:40Z

1

Here's a comparison of the performance of each of the options mentioned in the question/comments

http://jsperf.com/array-initialization-in-coffeescript

for me on Chrome 28

arr = []
arr.push(0) while arr.length isnt 100

is the fastest

and

[0..100].map -> 0

is the slowest.

That said, the slowest one is on the order of 100k ops/sec. Since initialization should be a relatively uncommon operation, I think its safe to say that performance here is less important than readability.

Personally I find the push version and map versions to be the most readable, but that should really be a decision made by you and whoever else will be working with/reading this code.

answered Aug 31, 2013 at 20:57

Ben McCormick

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