title: pandas update dataframe values if cell contains '-'
body: <p>I have a pandas Dataframe which has 46 columns, and 6 rows. </p>
  
  <pre><code>Index    Column1    Column2    Column3   Column4      ... # Cant type all 46 columns.
  2012     5626       fooo       -         barrr
  2013     5655h      booo       -         barr
  2014     5626d      zooo       -         -
  LTM      56         gooo       greed     -   
  </code></pre>
  
  <p>Is there a way for me to go through this Dataframe and update all the <code>-</code> values to be <code>0</code> or <code>null</code> values?</p>
  
  <p>I have tried:</p>
  
  <pre><code>for zzz in df.columns:  # since df.columns will return me the names of the columns
      if df_final[zzz].any() == '-':
          df_final[zzz] = 0
          print(df_final) 
  </code></pre>
  
  <p>However, this just prints everything out as it is. it does not convert <code>-</code> into <code>0 / null</code></p>