title: Sum an a nested array in an array of objects
body: <p>I have a react component with a state that looks like this:</p>
  
  <pre><code>this.state = {
              categoryGroups: [
                  {
                      groupName: 'Immediate Obligations',
                      budgeted: '5,000.00',
                      activity: '3,275.76',
                      subcategories: [
                          {
                              category: 'food',
                              budgeted: '500.00',
                              activity: '300.76'
                          },
                          {
                              category: 'rent',
                              budgeted: '1,000.00',
                              activity: '1,000.00'
                          }
                      ]
                  },
                  {
                      groupName: 'True Expenses',
                      budgeted: '2,000.00',
                      activity: '1,000.33',
                      subcategories: [
                          {
                              category: 'Car Insurance',
                              budgeted: '60.00',
                              activity: '60.00'
                          },
                          {
                              category: 'Gas',
                              budgeted: '100.00',
                              activity: '34.50'
                          }
                      ]
                  }
              ]
          }
  </code></pre>
  
  <p>I want to find the total budgeted amount for all of the subcategories in each category group. How can I do this?</p>