My application has different types of data about a fixed set of countries, kept in arrays of a consistent order.

data = 
  oranges: [1,2,3]
  apples: [1,2,3]
  cabbages: [1,2,3]

These arrays get bined by various criteria into new arrays, and I find myself wanting to write code like this:

fruit = []
for key, arr of data                  # For each array
  if key in ['oranges', 'apples']     # It it meets certain criteria
    for val, i in arr                 # Use the values in the creation of a new array
      fruit[i] += val

This doesn't work because if fruit[i] is not initialized += won't work.

There are various ways around this.

1) Fill the new fruit array with zeros first:

for i in [0..len]
  fruit[i] = 0

2) Check if fruit[i] exists:

if fruit[i]?
  fruit[i] += val 
else 
  fruit[i] = val

Neither of these seem elegant. I tried extracting approach 2) into a function but I have to admit that I couldn't quite get my head round it. I thought about passing in fruit, cloning it (with arr.slice(0)) and then setting fruit to the output, but it didn't feel right to do this on every iteration.

The data format is fixed, but other than that my question is "what is the best way of handling this?" I'm open to answers that use CoffeeScript and/or ECMAScript 5 and/or JQuery.

My application has different types of data about a fixed set of countries, kept in arrays of a consistent order.

data = 
  oranges: [1,2,3]
  apples: [1,2,3]
  cabbages: [1,2,3]

These arrays get bined by various criteria into new arrays, and I find myself wanting to write code like this:

fruit = []
for key, arr of data                  # For each array
  if key in ['oranges', 'apples']     # It it meets certain criteria
    for val, i in arr                 # Use the values in the creation of a new array
      fruit[i] += val

This doesn't work because if fruit[i] is not initialized += won't work.

There are various ways around this.

1) Fill the new fruit array with zeros first:

for i in [0..len]
  fruit[i] = 0

2) Check if fruit[i] exists:

if fruit[i]?
  fruit[i] += val 
else 
  fruit[i] = val

Neither of these seem elegant. I tried extracting approach 2) into a function but I have to admit that I couldn't quite get my head round it. I thought about passing in fruit, cloning it (with arr.slice(0)) and then setting fruit to the output, but it didn't feel right to do this on every iteration.

The data format is fixed, but other than that my question is "what is the best way of handling this?" I'm open to answers that use CoffeeScript and/or ECMAScript 5 and/or JQuery.

• javascript
• coffeescript

• Where is array defined? – elclanrs Commented Aug 22, 2013 at 7:44
• @elclanrs sorry. Fixed typo. array is arr – Derek Hill Commented Aug 22, 2013 at 8:10
• 2 fruit[i] = fruit[i] + 1 || 1? – david Commented Aug 22, 2013 at 8:15

1 Answer 1

You can initialize element of the array with using ||= or ?= operator:

fruit[i] ||= 0
fruit[i] += val

The only difference is that ?= checks for null or undefined and ||= checks for any false value.