Question

What’s the closest equivalent to ruby’s Hash#reject/delete_if method?

{a:1, b:2, c:3, d:4}.reject { |k,v| v > 2 }
=> {:a=>1, :b=>2}

this quick version uses key, value of <Object> but it’s not elegant, and lacks the ability to pass an arbitrary condition (as a block or otherwise)

params = {a:1, b:2, c:3}
filter = (hash)->
    result = {}
    (result[key] = value unless value > 2) for key, value of params
    result

console.log(filter(params))

underscore has a similar _.omit method, but only works on keys.

Answer 1

Unfortunately CoffeeScript comprehensions always generate arrays. You could use Underscore’s object method to transform a [key, value] array into an object:

obj = {a:1, b:2, c:3, d:4}
_.object([k, v] for k, v of obj when v <= 2) # -> {a:1, b:2}

I’d recommend you code your own method for this specific purpose though:

reject = (obj, predicate) ->
  res = {}
  res[k] = v for k, v of obj when not predicate k, v
  res

reject {a:1, b:2, c:3, d:4}, (k, v) -> v > 2 # -> {a:1, b:2}