>>> df.tip_amount.corr(df.payment_type == 2).compute()
/opt/anaconda/lib/python2.7/site-packages/dask/dataframe/core.pyc in corr(self, other, method, min_periods)
   1235             raise NotImplementedError("Only Pearson correlation has been "
   1236                                       "implemented")
-> 1237         df = concat([self, other], axis=1)
   1238         return cov_corr(df, min_periods, corr=True, scalar=True)
   1239 

/opt/anaconda/lib/python2.7/site-packages/dask/dataframe/multi.pyc in concat(dfs, axis, join, interleave_partitions)
    552     else:
    553         if axis == 1:
--> 554              raise ValueError('Unable to concatenate DataFrame with unknown '
    555                               'division specifying axis=1')
    556         else:

ValueError: Unable to concatenate DataFrame with unknown division specifying axis=1

>>> df[['tip_amount', 'payment_type']].corr().compute()
               tip_amount    payment_type
tip_amount       0.999169       -0.033852
payment_type    -0.033852        8.420302

>>> df.head(1000)[['tip_amount', 'payment_type']].corr()
               tip_amount    payment_type
tip_amount       1.000000       -0.559584
payment_type    -0.559584        1.000000