code: def dataset_nan_locs(ds):
      
      ans = []
      for sampnum, sample in enumerate(ds):
          if pd.isnull(sample).any():
              ans += [{
                  'sample': sampnum,
                  'input':  pd.isnull(sample[0]).nonzero()[0],
                  'output': pd.isnull(sample[1]).nonzero()[0],
                  }]
      return ans
docs: from http://stackoverflow.com/a/14033137/623735
      # gets the indices of the rows with nan values in a dataframe
      pd.isnull(df).any(1).nonzero()[0]