title: Problem in Appending dictionary to Dataframe
body: <p>I have this dataframe(<code>User</code> is the index)(Also, this a part of a bigger dataframe, so <code>Series</code> cannot be used):</p>
  <pre><code>User  Score
  A         5
  B        10
  A         4
  C         8
  </code></pre>
  <p>I want to add <code>Score</code> of duplicate <code>User</code>s.</p>
  <p>So First I calculate the Sum of <code>Score</code> of the duplicate <code>User</code>:</p>
  <pre class="lang-py prettyprint-override"><code>sum = df.loc['A'].sum()
  </code></pre>
  <p>Then I drop the duplicate rows:</p>
  <pre class="lang-py prettyprint-override"><code>df.drop('A',inplace=True)
  </code></pre>
  <p>Then I append the new values as a dictionary to the dataframe:</p>
  <pre class="lang-py prettyprint-override"><code>dic = {'User':'A','Score':10}
  df = df.append(dic,ignore_index=True)
  </code></pre>
  <p>But I get this dataframe:</p>
  <pre><code>   Score User
  0     10  NaN
  1      8  NaN
  2     10    A
  </code></pre>
  <p>The default autoincrement values has replaced <code>User</code> as index and values of <code>User</code> are non <code>NaN</code>.
  The expected dataframe would be:</p>
  <pre><code>User  Score
  B        10
  C         8
  A         9
  </code></pre>