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 variableconst d3 = require('d3');Â
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" }]Â
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 variableconst d3 = require('d3');Â
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" }]Â
const gfg = d3.rollup(data, g => g.length, d => d.name, d => d.date);Â
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 }
}
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