You should read this question: Javascript as a functional language There are lots of useful links, including: Use functional programming techniques to write elegant JavaScript The Little JavaScripter Higher-Order JavaScript Eloquent JavaScript, Chapter 6: Functional Programming Now, for my opinion. A lot of people misunderstand JavaScript, possibly because its syntax looks like most other programming … Read more
Here’s the Underscore way to do it – this augments the core Underscore function with one that accepts an iterator function: // save a reference to the core implementation var indexOfValue = _.indexOf; // using .mixin allows both wrapped and unwrapped calls: // _(array).indexOf(…) and _.indexOf(array, …) _.mixin({ // return the index of the first … Read more
Assuming the original list is contained in a variable named list: _ .chain(list) .groupBy(‘type’) .map(function(value, key) { return { type: key, foods: _.pluck(value, ‘food’) } }) .value();
The following will: create a new array that contains all the elements of c1 and c2. See union. from that mix, create a new array that contains only the unique elements. See uniq. Note that this would work only if all your objects have the property a. _.uniq(_.union(c1, c2), false, function(item, key, a){ return item.a; … Read more
you should use _.filter() before _.map() var filteredArray = _.filter(myArray,function(obj) { return !obj.ignore; }); var finalArray = _.map(filteredArray, function(obj) { return obj.myProperty; });
Plain javascript (ES2015), using Set const list = [{ x: 1, y: 2 }, { x: 3, y: 4 }, { x: 5, y: 6 }, { x: 1, y: 2 }]; const uniq = new Set(list.map(e => JSON.stringify(e))); const res = Array.from(uniq).map(e => JSON.parse(e)); document.write(JSON.stringify(res));
I know you asked for Underscore.js solutions, but you don’t need it for this. Here’s a oneliner using ES7 object spread operator and dynamic keys. keys.reduce((obj, k, i) => ({…obj, [k]: values[i] }), {})
Underscore has the _.groupBy function which should do exactly what you want: var groups = _.groupBy(occurences, function (date) { return moment(date).startOf(‘day’).format(); }); This will return an object where each key is a day and the value an array containing all the occurrences for that day. To transform the object into an array of the same … Read more
Why all people gets over-complicated here? const people = [ { name: ‘Alejandro’, budget: 56 }, { name: ‘Juan’, budget: 86 }, { name: ‘Pedro’, budget: 99 }, ]; const average = _.meanBy(people, (p) => p.budget); console.log(average); <script src=”https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js”></script> As per the docs: https://lodash.com/docs/#meanBy
Update: See the comments below, this is not a good solution in most cases. Someone kindly answered in the issue I created. Here’s his answer, inlined: _.sortBy(data, function(item) { return [item.sortData.a, item.sortData.b]; }); I didn’t realize that you’re allowed to return an array from that function. The documentation doesn’t mention that.