title: Merging two time data frames one after the other
body: <p>What I am trying to do is to merge two data frames with observations of different variables by data.</p>
  
  <p>The first data frame contains observations for the period between January 2019 till January 2020
  The second data frame contains observations for the period between January 2020 till December 2020. Namely, the observations for the month of January 2020 are present in both dataframes. In the example below two of the last observation in <code>dataframe 1</code> are identical to the two first observations in <code>dataframe 2</code>.  </p>
  
  <pre><code>      dataframe 1
  Date         V1    V2
  2019-01-01    x     y
  2019-01-03    x     z
  2020-01-01    x     y
  2020-01-02    v     x
  
  
       dataframe 2 
   Date         V1    V2
  2020-01-01    x     y
  2020-01-02    v     x
  2020-01-03    v     x
  2020-01-04    n     j
  2020-01-06    b     h
  </code></pre>
  
  <p>Out of these two data frames I want to create one dataframe that spans from January 2019 till December 2020. Namely, from the beginning of <code>dataframe 1</code> till the end of <code>dataframe 2</code>. </p>
  
  <p>But, the goal is to merge the two dataframes in a way <strong>that if there are any same observations then only one observation of the two will remain in the new dataframe</strong>. While <strong>if there is an observation that is present in only one of the original dataframes it will remain in the new one</strong>. In other words, I want to avoid duplicates but preserve unique observations. I think its called full join.
  The new one should like like this</p>
  
  <pre><code>     NewDataFRAME
  2019-01-01    x     y
  2019-01-03    x     z
  2020-01-01    x     y
  2020-01-02    v     x
  2020-01-03    v     x
  2020-01-04    n     j
  2020-01-06    b     h
  </code></pre>
  
  <p>The observations presented in both of the original dataframes are present only once in the new one.  </p>
  
  <p>I am not familiar with the correct terminology if you wish to feel free to explain it.</p>