D3.js rollups() method Last Updated : 14 Sep, 2020 Comments Improve Suggest changes Like Article Like Report With the help of d3.rollups() method, we can get the reduced nested array instead of map from iterable data structure having key and values. Syntax: d3.rollups(iterable, reduce, ...keys) Return value: It will return the reduced nested array instead of map. Note: To execute the below examples you have to install the d3 library by using the command prompt for the following command. npm install d3 Example 1: In this example, we can see that by using d3.rollups() method we are able to get the reduced nested array instead of nested map from an iterable data structure having key and values. JavaScript // Defining d3 contrib variable var d3 = require('d3'); data = [ {name: "ABC", amount: "34.0", date: "11/12/2015"}, {name: "DEF", amount: "120.11", date: "11/12/2015"}, {name: "MNO", amount: "12.01", date: "01/04/2016"}, {name: "ABC", amount: "34.05", date: "01/04/2016"} ] var gfg = d3.rollups(data, g => g.length, d => d.name); console.log(gfg); Output: [ [ 'ABC', 2 ], [ 'DEF', 1 ], [ 'MNO', 1 ] ] Example 2: JavaScript // Defining d3 contrib variable var d3 = require('d3'); data = [ {name: "ABC", amount: "34.0", date: "11/12/2019"}, {name: "DEF", amount: "120.11", date: "11/02/2020"}, {name: "MNO", amount: "12.01", date: "01/04/2020"}, {name: "DEF", amount: "34.05", date: "03/04/2020"} ] var gfg = d3.rollups(data, g => g.length, d => d.name, d => d.date); console.log(gfg); Output: [ [ 'ABC', [ [Array] ] ], [ 'DEF', [ [Array], [Array]]], [ 'MNO', [ [Array] ] ] ] Comment More infoAdvertise with us J jitender_1998 Follow Improve Article Tags : JavaScript Web Technologies D3.js Explore JavaScript Tutorial 8 min read JavaScript BasicsIntroduction to JavaScript 4 min read JavaScript Versions 2 min read How to Add JavaScript in HTML Document? 3 min read JavaScript Syntax 6 min read JavaScript Output 4 min read JavaScript Comments 2 min read JS Variables & DatatypesVariables and Datatypes in JavaScript 6 min read Global and Local variables in JavaScript 4 min read JavaScript Let 6 min read JavaScript const 5 min read JavaScript Var Statement 7 min read JS OperatorsJavaScript Operators 5 min read Operator precedence in JavaScript 2 min read JavaScript Arithmetic Operators 5 min read JavaScript Assignment Operators 5 min read JavaScript Comparison Operators 5 min read JavaScript Logical Operators 5 min read JavaScript Bitwise Operators 5 min read JavaScript Ternary Operator 4 min read JavaScript Comma Operator 2 min read JavaScript Unary Operators 4 min read JavaScript in and instanceof operators 3 min read JavaScript String Operators 3 min read JS StatementsJavaScript Statements 4 min read JavaScript if-else 3 min read JavaScript switch Statement 4 min read JavaScript Break Statement 2 min read JavaScript Continue Statement 1 min read JavaScript Return Statement 4 min read JS LoopsJavaScript Loops 3 min read JavaScript For Loop 4 min read JavaScript While Loop 3 min read JavaScript For In Loop 3 min read JavaScript for...of Loop 3 min read JavaScript do...while Loop 4 min read JS Perfomance & DebuggingJavaScript | Performance 4 min read Debugging in JavaScript 4 min read JavaScript Errors Throw and Try to Catch 2 min read JS ObjectObjects in Javascript 4 min read Object Oriented Programming in JavaScript 3 min read JavaScript Objects 6 min read Creating objects in JavaScript 5 min read JavaScript JSON Objects 3 min read JavaScript Object Reference 4 min read JS FunctionFunctions in JavaScript 4 min read How to write a function in JavaScript ? 4 min read JavaScript Function Call 2 min read Different ways of writing functions in JavaScript 3 min read Difference between Methods and Functions in JavaScript 3 min read Explain the Different Function States in JavaScript 3 min read JavaScript Function Complete Reference 3 min read JS ArrayJavaScript Arrays 7 min read JavaScript Array Methods 7 min read Best-Known JavaScript Array Methods 6 min read Important Array Methods of JavaScript 7 min read JavaScript Array Reference 4 min read Like