Question

I’m trying to get my head around using CoffeeScript comprehensions as efficiently as possible. I think I have basic mapping down — turning one list into another — but searching still seems verbose to me.

Say I have a map of items to shops:

shopMap:
  toyStore: ["games", "puzzles"]
  bookStore: ["novels", "picture books"]

and, given an item, I want to find out which shop it’s in. What’s the best way of doing that in CoffeeScript?

Here’s how I could do in in JavaScript:

var shop = findShop(item);

function findShop(item) {
   for (shop in shopMap)
      itemList = shopMap[shop]
      for (i = 0, ii = itemList.length; i<ii; i++) {
         if (itemList[i] === item) {
            return shop;
         }
      }
  }
}

I used a function to allow it to quickly break out of the loops with the return statement, instead of using breaks, but the function is kind of fugly as this is only being used once.

So is there a shorter CS equivalent preferably one that doesn’t require creating a new function?

Answer 1

You can try this:

findShop = (item) ->
  for shop, items of shopMap
    return shop if item in items

If you really want to try with a list comprehension, this is equivalent:

findShop = (item) ->
  (shop for shop, items of shopMap when item in items)[0]

But i think the first one reads better (and also doesn’t need to generate an intermediate array for the results). This would be a better approach IMO if you wanted to find all shops for a given item:

findShops = (item) ->
  shop for shop, items of shopMap when item in items