PythonのPandasで値の代入のエラー

Question

def main():
    features_df = pd.DataFrame()
    features_df['labels'] = [0,1,2,0,1]
    features_df['T1'][0] = 1
    features_df['T2'][0] = 1
    print(features_df)

if __name__ == '__main__':
    main()

想定している結果
   labels  T1  T2
0       0   1   1
1       1   Nan Nan
2       2   Nan Nan
3       0   Nan Nan
4       1   Nan Nan

以上のコードを実行すると、

Traceback (most recent call last):
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2393, in get_loc
    return self._engine.get_loc(key)
  File "pandas/_libs/index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5239)
  File "pandas/_libs/index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5085)
  File "pandas/_libs/hashtable_class_helper.pxi", line 1207, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas/_libs/hashtable.c:20405)
  File "pandas/_libs/hashtable_class_helper.pxi", line 1215, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas/_libs/hashtable.c:20359)
KeyError: 'T1'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "pa.py", line 94, in <module>
    main()
  File "pa.py", line 89, in main
    features_df['T1'][1] = 1
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/frame.py", line 2062, in __getitem__
    return self._getitem_column(key)
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/frame.py", line 2069, in _getitem_column
    return self._get_item_cache(key)
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/generic.py", line 1534, in _get_item_cache
    values = self._data.get(item)
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/internals.py", line 3590, in get
    loc = self.items.get_loc(item)
  File "/Users/anaconda/lib/python3.6/site-packages/pandas/core/indexes/base.py", line 2395, in get_loc
    return self._engine.get_loc(self._maybe_cast_indexer(key))
  File "pandas/_libs/index.pyx", line 132, in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5239)
  File "pandas/_libs/index.pyx", line 154, in pandas._libs.index.IndexEngine.get_loc (pandas/_libs/index.c:5085)
  File "pandas/_libs/hashtable_class_helper.pxi", line 1207, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas/_libs/hashtable.c:20405)
  File "pandas/_libs/hashtable_class_helper.pxi", line 1215, in pandas._libs.hashtable.PyObjectHashTable.get_item (pandas/_libs/hashtable.c:20359)
KeyError: 'T1'

このようなエラーがでてしまいます。
原因はなにが考えられるでしょうか。

よろしくお願い致します。

Answer 1

loc[]をお使いください

import pandas as pd

features_df = pd.DataFrame()
features_df['labels'] = [0,1,2,0,1]
features_df.loc[0, 'T1'] = 1
features_df.loc[0, 'T2'] = 1
print(features_df)
#   labels   T1   T2
#0       0  1.0  1.0
#1       1  NaN  NaN
#2       2  NaN  NaN
#3       0  NaN  NaN
#4       1  NaN  NaN

Comments

[gymgym]

回答ありがとうございます。
参考にさせていただきます。

Answer 2

import pandas as pd

d = {"labels": [0,1,2,0,1], "T1": None, "T2":None}
df = pd.DataFrame(d)
df["T1"][0] = 1
df["T2"][0] = 1
"""
     T1    T2  labels
0     1     1       0
1  None  None       1
2  None  None       2
3  None  None       0
4  None  None       1
"""

Comments

[gymgym]

回答ありがとうございます。
参考にさせていただきます。