title: Typescript reduce object array by specific value
body: <p>I have this:</p>
  
  <pre><code>0: {orderType: "orderType1", orderCount: 0, orderDate: 47}
  1: {orderType: "orderType1", orderCount: 21, orderDate: 47}
  2: {orderType: "orderType1", orderCount: 3, orderDate: 47}
  3: {orderType: "orderType1", orderCount: 5, orderDate: 48}
  4: {orderType: "orderType1", orderCount: 32, orderDate: 48}
  5: {orderType: "orderType1", orderCount: 12, orderDate: 48}
  </code></pre>
  
  <p>and I would like to achieve this:</p>
  
  <pre><code>0: {orderType: "orderType1", orderCount: 24, orderDate: 47}
  1: {orderType: "orderType1", orderCount: 49, orderDate: 48}
  </code></pre>
  
  <p>Basically I want to 'combine' or 'reduce' the entries by combining the orderCount based on orderDate.</p>
  
  <p>Apologies if combine or reduce are not the right terms here.</p>