title: Concat strings with different amount of values
body: <p>I am having five strings with a different amount of RangeIndex. String 1 for example could have the following data:</p>
  <pre><code>20160101   1.08526
  20160102   1.08535
  20160103   1.09052
  20160104   1.08659
  </code></pre>
  <p>String 2 is as follows</p>
  <pre><code>20160101   150.0659
  20160103   145.8063
  20160104   143.5892
  </code></pre>
  <p>with the normal concat function I would get the following result</p>
  <pre><code>20160101   1.08526 20160101 150.0659
  20160102   1.08535 20160103 145.8063
  20160103   1.09052 20160104 143.5892
  20160104   1.08659 
  </code></pre>
  <p>The result I am looking for should be as follow</p>
  <pre><code>20160101   1.08526 20160101 150.0659
  20160102   1.08535 20160102 150.0659
  20160103   1.09052 20160103 145.8063
  20160104   1.08659 20160104 143.5892
  </code></pre>
  <p>This means that the combination of the two strings should put the right data together with the right date. If there is an empty field the system should chose the previous value to fill the gap.</p>
  <p>How can that be done?</p>