title: Pandas adding NA changes column from float to object
body: <p>I have a dataframe with a column that is of type float64. Then when I run the following it converts to object, which ends up messing with a downstream calculation where this is the denominator and there are some 0s:</p>
  <pre><code>df.loc[some criteria,'my_column'] = pd.NA
  </code></pre>
  <p>After this statement, my column is now of type object. Can someone explain why that is, and how to correct this? I'd rather do it right the first time rather than adding this to the end:</p>
  <pre><code>df['my_column'] = df['my_column'].astype(float)
  </code></pre>
  <p>Thanks.</p>