Group by date

.js

import React from "react";
import ReactDOM from "react-dom";

function App() {
  const orders = [
    { date: 1556396396, project: "Project 1" },
    { date: 1556396416, project: "Project 2" },
    { date: 1552186577, project: "Project 3" },
    { date: 1554064562, project: "Project 4" },
    { date: 1556396473, project: "Project 5" },
    { date: 1552256702, project: "Project 6" },
    { date: 1552186855, project: "Project 8" }
  ];

  const groupBy = func => array =>
    array.reduce((acc, cur) => {
      const key = func(cur);
      acc[key] = (acc[key] || []).concat(cur);
      return acc;
    }, {});

  const orderDate = order => new Date(order.date * 1000).toDateString();
  const groupByDate = groupBy(orderDate);
  const groupedOrders = groupByDate(orders);

  return Object.keys(groupedOrders).map(date => (
    <>
      <div>{date}</div>
      {groupedOrders[date].map(order => (
        <div>{order.project}</div>
      ))}
    </>
  ));
}

const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);