filter object with preserve keys

filter-object-preserve-keys.md

I have a object

var obj = {
  1: [5, 7, 8],
  7: [4, 2],
  10: [],
  19: [4]
}; // each key:value is id: array

I want to filter the object: remove keys have empty array and preserve keys. If I use _.filter, result is not expected:

_.filter(obj, function(ids) { return ids.length > 0;});
_.filter(obj, _.negate(_.isEmpty)); // or the code

// result is
// {
//  [5, 7, 8],
//  [4, 2],
//  [4],
// }

But I want expected result is

{
  1: [5, 7, 8],
  7: [4, 2],
  19: [4]
}

There are 2 ways:

1. short code. I'm using it, of course

_.pick(obj, _.negate(_.isEmpty));

2. long code. Just reference.

_.chain(obj)
.pairs()
.filter(function(value){ return !_.isEmpty(value[1]);})
.object()
.value()