title: round a single column in pandas
body: <p>Is there a way to round a single column in pandas without affecting the rest of the dataframe?</p>
  <pre><code>&gt;&gt;&gt; print(df)
    item  value1  value2
  0    a    1.12     1.3
  1    a    1.50     2.5
  2    a    0.10     0.0
  3    b    3.30    -1.0
  4    b    4.80    -1.0
  </code></pre>
  <p>I have tried the following:</p>
  <pre><code>&gt;&gt;&gt; df.value1.apply(np.round)
  0    1
  1    2
  2    0
  3    3
  4    5
  5    5
  </code></pre>
  <p>What is the correct way to make data look like this:</p>
  <pre><code>  item  value1  value2
  0    a       1     1.3
  1    a       2     2.5
  2    a       0     0.0
  3    b       3    -1.0
  4    b       5    -1.0
  5    c       5     5.0
  </code></pre>