D3.js rollup() method

With the help of d3.rollup() method, we can get the reduced map from an iterable data structure having keys and values.

Syntax:

d3.rollup(iterable, reduce, ...keys)

Return value: It will return the reduced map from iterables.

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 the d3.rollup() method, we are able to get the reduced map from an iterable data structure having keys and values.

Javascript

// Defining d3 contrib variable
const 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" }
]

let gfg = d3.rollup(data, g => g.length, d => d.amount);
console.log(gfg);

Output:

Map { '34.0' => 1, '120.11' => 1, '12.01' => 1, '34.05' => 1 }

Example 2:

Javascript

// Defining d3 contrib variable
const 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" }
]

const gfg = d3.rollup(data, g => g.length, d => d.name, d => d.date);

console.log(gfg);

Output:

Map {
  'ABC' => Map { '11/12/2019' => 1 },
  'DEF' => Map { '11/02/2020' => 1, '03/04/2020' => 1 },
  'MNO' => Map { '01/04/2020' => 1 } 
  }