Use Underscore.js to retrieve top n elements from array ranked by some property

Question

I have an array of objects in javascript. Each object is of the form

obj {
    location: "left", // some string
    weight: 1.25 // some real, positive number
}

Let us assume the length of the array is greater than 500.

I want to return a filtered copy of the array where only the top 500 elements as ranked by the weight property are present. In other words, I want the array with objects with the 500 highest weights

What is the clean way to do this with underscore?

Answer 1

You can do it with normal javascript, put this in a function and it should work. Just pass in the array you want to sort as myArray. Sorry for lack of explanation, on my phone.

var sorted = myArray.sort(function (a, b) {
    return a.weight - b.weight; // sort by weight, low to heigh
}).reverse(); // then reverse to get high to low

return sorted.slice(0, 500); // slice the first 500

Answer 2

You can use sortBy() to sort the array in descending order by weight and use first() to take the first 500...

var top500 = _.chain(myObjects)
              .sortBy(function(item) { return item.weight * -1; })
              .first(500)
              .value();