title: Lodash - Find deep in array of object
body: <p>I have an array of an object like this</p>
  
  <pre><code>[
      {
          'a': 10,
          elements: [
              {
                  'prop': 'foo',
                  'val': 10
              },
              {
                  'prop': 'bar',
                  'val': 25
              },
              {
                  'prop': 'test',
                  'val': 51
              }
          ]
      },
      {
          'b': 50,
          elements: [
              {
                  'prop': 'foo',
                  'val': 30
              },
              {
                  'prop': 'bar',
                  'val': 15
              },
              {
                  'prop': 'test',
                  'val': 60
              }
          ]
      },
  ]
  </code></pre>
  
  <p>What I need is sum the property <code>Val</code> when <code>prop</code> is <code>foo</code>.
  So, I have to search through elements and get all objects where <code>prop</code> is <code>foo</code>. With this objects, I should sum the <code>val</code> property.</p>
  
  <p>I tried to use many combinations of <code>_.find</code>, <code>_.pick</code> and so on, but I don't get the right result. Can someone help me?</p>