add feature names

Signed-off-by: weiwee <wbwmat@gmail.com>

python/fate/arch/dataframe/ops/_histogram.py

@@ -16,19 +16,21 @@
 import functools
 
 from fate.arch.tensor.inside import Hist
-from ._compress_block import compress_blocks
+
 from .._dataframe import DataFrame
 from ..manager import BlockType, DataManager
+from ._compress_block import compress_blocks
 
 
 def hist(df: DataFrame, targets):
     data_manager = df.data_manager
+    column_names = data_manager.infer_operable_field_names()
 
     block_table, data_manager = _try_to_compress_table(df.block_table, data_manager)
     block_id = data_manager.infer_operable_blocks()[0]
 
     def _mapper(blocks, target, bid: int = None):
-        histogram = Hist()
+        histogram = Hist(column_names)
         histogram.update(blocks[bid], target)
 
         return histogram

python/fate/arch/tensor/inside/_op_hist.py

@@ -2,7 +2,8 @@
 
 
 class Hist:
-    def __init__(self):
+    def __init__(self, feature_names):
+        self.feature_names = feature_names
         self.data: typing.Dict[int, typing.Dict[int, typing.Any]] = {}
 
     def update(self, features, labels):
@@ -38,7 +39,7 @@ def cumsum(self):
         return self
 
     def __sub__(self, other: "Hist"):
-        out = Hist()
+        out = Hist(self.feature_names)
         for j in self.data:
             out.data[j] = {}
             for v in self.data[j]:
@@ -48,6 +49,9 @@ def __sub__(self, other: "Hist"):
                     out.data[j][v] = self.data[j][v] - other.data[j][v]
         return out
 
+    def to_dict(self):
+        return {name: self.data[i] for i, name in enumerate(self.feature_names)}
+
 
 if __name__ == "__main__":
     import numpy as np