coffeescript for loop refactoring

Question

I am quite new to coffeescript and I am wondering if any more experienced users could point suggest a refactoring for the following code:

splitCollection: =>
  maxLength = Math.ceil(@collection.length / 3)

  sets = Math.ceil(@collection.length / maxLength)
  start = 0    

  for x in [1..sets]   
    if x != sets
      @render new BusinessUnits(@collection.models.slice(start, (maxLength + start)))
    else
      @render new BusinessUnits(@collection.models.slice(start, (@collection.length)))
    start+= maxLength

There does not appear to be a while loop in coffeescript which seems to suggest a better mechanism.

Any suggestions appreciated.

Brian Genisio · Accepted Answer · 2011-11-21 11:06:23Z

5

Looks like you are using Backbone.js, which includes Underscore.js, which has the groupBy function.

You could create a "bucketNumber" function:

bucketNumber = (value, index) ->
    Math.floor( index / @collection.length * 3 )

Then group your collection:

sets = @collection.groupBy bucketNumber

Now, assuming ten items, sets should look something like this:

{0: [{}, {}, {}], 1: [{}, {}, {}], 2: [{}, {}, {}, {}]}

From here, it becomes rather straight-forward

for bucketNumber, bucket of sets
    @render new BusinessUnits( bucket )

Here is a jsFiddle showing it in action

edited Nov 21, 2011 at 11:06

answered Nov 21, 2011 at 10:44

Brian Genisio

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1 Comment

dagda1 Over a year ago

That is a nice answer and what I will probably use but I am trying to understand coffeescript better.

Ricardo Tomasi · Accepted Answer · 2011-11-21 12:46:11Z

1

You don't need to keep track of your position twice, x is enough:

splitCollection: =>
    setSize = Math.ceil @collection.length / 3
    sets = Math.ceil @collection.length / maxLength

    for x in [1..sets]
        @render new BusinessUnits @collection.models[x * setSize...(x+1) * setSize]

Note that there is nothing wrong with passing slice an end greater than the array length.

answered Nov 21, 2011 at 12:46

Ricardo Tomasi

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Comments

tokland · Accepted Answer · 2011-11-21 16:22:42Z

0

If I understand your code, you want to split an array in 3 parts (the last one can have less items). In this case write the reusable abstraction for the task. Using underscore:

splitCollection: =>
  group_size = Math.ceil(@collection.size() / 3)
  _.each _(@collection.models).inGroupsOf(group_size), (group) ->
    @render(new BusinessUnits(group))

_.inGroupsOf can be written:

_.mixin({
  inGroupsOf: function(array, n) {
    var output = [];
    for(var index=0; index < array.length; index += n) {
      output.push(array.slice(index, index+n));
    }
    return output;
  }
});

edited Nov 21, 2011 at 16:22

answered Nov 21, 2011 at 15:49

tokland

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