underscore.js filter an array of objects, based on another
I am trying to filter an array of objects, based on another. The common property id id.
I am not sure filter + each is the best way to do it or map reduce. Anyway, below code doesn’t work as out is empty list.
var aaa = [
{name: "AAA", id: 845},
{name: "BBB", id: 839},
{name: "CCC", id: 854}
];
var bbb = [
{id: 839},
{id: 854}
];
var out = _.filter(aaa, function(val){
return _.each(this, function(val2){
return val['id'] === val2['id']
});
}, bbb);
Just create a “set” of the valid ids and use that “set” to do the filtering:
var aaa = [
{name: "AAA", id: 845},
{name: "BBB", id: 839},
{name: "CCC", id: 854}
];
var bbb = [
{id: 839},
{id: 854}
];
var ids = {};
_.each(bbb, function (bb) { ids[bb.id] = true; });
var out = _.filter(aaa, function (val) {
return ids[val.id];
}, bbb);
Filling ids is fast, it’s in n * amortized O(1), i.e O(n). Same holds for the filtering.
If you use each(…) in the inner loop, you will have O(n²). For bigger data sets this would become very slow. Also the additional nesting make the code more difficult to read/understand at first glance.
See that code snipped in action: http://jsfiddle.net/SMtX5/
you can use _.find to filter:
_.filter(aaa, function(a){
return _.find(bbb, function(b){
return b.id === a.id;
});
});
You can use _.some(list, [iterator], [context]).
It returns true if any of the values in the list pass the iterator truth test.
var out = _.filter(aaa, function(val){
return _.some(this,function(val2){
return val2['id'] === val['id'];
});
}, bbb);
Here is jsfiddle. http://jsfiddle.net/h98ej/
bbb = bbb.map(_ => _.id) && aaa.filter(_ => bbb.indexOf( _.id ) > -1)
You just need pure JS array functions to do that assuming your use case.
