Load data and labels into arrays.

def load_data_batch(self, data_batch):
        """Load data and labels into arrays."""
        if self.sym_gen is not None:
            key = data_batch.bucket_key
            if key not in self.execgrp_bucket:
                # create new bucket entry
                symbol = self.sym_gen(key)
                execgrp = DataParallelExecutorGroup(symbol, self.arg_names,
                                                    self.param_names, self.ctx,
                                                    self.slices, data_batch,
                                                    shared_group=self.execgrp)
                self.execgrp_bucket[key] = execgrp

            self.curr_execgrp = self.execgrp_bucket[key]
        else:
            self.curr_execgrp = self.execgrp

        self.curr_execgrp.load_data_batch(data_batch)