How to use Underscore.js filter with an object?

问题:

I have an object like so:

> Object
  > [e-mail]: Array[100]
  > [e-mail]: Array[4]
    > 0
       id : 132
       selected : true
    > 1
       id : 51
       selected : false

etc..

How can I use the underscore _.filter() to return back only the items where selected === true?

I've never had the need to go down to layers with _.filter(). Something like

var stuff = _.filter(me.collections, function(item) {
    return item[0].selected === true;
});

Thank you

回答1:

If you want to pull all array elements from any e-mail address where selected is true, you can iterate like so:

var selected = [];

for (email in emailLists) {
    selected.concat(_.filter(emailLists[email], function (item) {
        return item.selected === true;
    }));
}

If you only want to pull the arrays where all elements are selected, you might instead do something like this:

var stuff = _.filter(me.collections, function(item) {
    return _.all(item, function (jtem) { 
        jtem.selected === true;
    });
});

回答2:

Underscore's filter method will work on an object being used as a hash or dictionary, but it will return an array of the object's enumerable values and strip out the keys. I needed a function to filter a hash by its values that would preserve the keys, and wrote this in Coffeescript:

hash_filter: (hash, test_function) ->
  keys = Object.keys hash

  filtered = {}
  for key in keys
    filtered[key] = hash[key] if test_function hash[key]
  filtered

If you're not using Coffeescript, here's the compiled result in Javascript, cleaned up a little:

hash_filter = function(hash, test_function) {
  var filtered, key, keys, i;
  keys = Object.keys(hash);
  filtered = {};
  for (i = 0; i < keys.length; i++) {
    key = keys[i];
    if (test_function(hash[key])) {
      filtered[key] = hash[key];
    }
  }
  return filtered;
}


hash = {a: 1, b: 2, c: 3};
console.log((hash_filter(hash, function(item){return item > 1;})));
// Object {b=2, c=3}

TL; DR: Object.keys() is great!

回答3:

I have an object called allFilterValues containing the following:

{"originDivision":"GFC","originSubdivision":"","destinationDivision":"","destinationSubdivision":""}

This is ugly but you asked for an underscore based way to filter an object. This is how I returned only the filter elements that had non-falsy values; you can switch the return statement of the filter to whatever you need:

    var nonEmptyFilters = _.pick.apply({}, [allFilterValues].concat(_.filter(_.keys(allFilterValues), function(key) {
        return allFilterValues[key];
    })));

Output (JSON/stringified):

{"originDivision":"GFC"}

回答4:

Maybe you want a simplest way

_.filter(me.collections, { selected: true})