title: How to use function for strings using Dask?
body: <p>I have a big data set and recently got introduced to Dask. I am trying to tokenise the text in each row.
  This is very easy to do in pandas as shown below, but I having an error saying</p>
  <p>AttributeError: 'DataFrame' object has no attribute 'lower' when I try to use Dask ( see the second group of codes below)</p>
  <pre><code>import pandas as pd
  import dask 
  import dask.dataframe as dd
  
   def to_lower(text):
          return text.lower()
  
  df_2016 = pd.read_csv(&quot;2016_Cleaned_DroppedDup.csv&quot;)
  df_2016['token2'] = df_2016['token2'].apply(lambda x: pr.to_lower(x))
  </code></pre>
  <p>With DASK:</p>
  <pre><code>df_2016 = dd.from_pandas(df_2016, npartitions = 4 * multiprocessing.cpu_count())
  df_2016 = df.2016.map_partitions.(lambda df: df.apply(lambda x: pr.to_lower(x))).compute(scheduler = 'processes')
  </code></pre>