D3.js index() method

With the help of d3.index() method, we can get the map having key as an element but the change is that we get object as unique values instead of an array.

Syntax:

d3.index(iterable, ...keys)

Return value: It returns the map of objects.

Note: To execute the below examples you have to install the d3 library by using the command prompt with the following command.

npm install d3

Example 1: In this example we can see that by using d3.index() method, we are able to get the map having key as element and value as object.

// 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: "XYZ", amount: "34.05",  date: "01/04/2016"}
]

var gfg = d3.index(data, d => d.name);

console.log(gfg);

Output:

Map {
  'ABC' => { name: 'ABC', amount: '34.0', date: '11/12/2015' },
  'DEF' => { name: 'DEF', amount: '120.11', date: '11/12/2015' },
  'MNO' => { name: 'MNO', amount: '12.01', date: '01/04/2016' },
  'XYZ' => { name: 'XYZ', amount: '34.05', date: '01/04/2016' } }

Example 2:

// 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: "XYZ", amount: "34.05",  date: "03/04/2020"}
]

var gfg = d3.index(data, d => d.name, d => d.date);

console.log(gfg);

Output:

Map {
  'ABC' => Map {
    '11/12/2019' => { name: 'ABC', amount: '34.0', date: '11/12/2019' } },
  'DEF' => Map {
    '11/02/2020' => { name: 'DEF', amount: '120.11', date: '11/02/2020' } },
  'MNO' => Map {
    '01/04/2020' => { name: 'MNO', amount: '12.01', date: '01/04/2020' } },
  'XYZ' => Map {
    '03/04/2020' => { name: 'XYZ', amount: '34.05', date: '03/04/2020' } } }