我想用 Python 对数据进行切片。对我的数据帧进行切片这一非常基本的任务会向我抛出意外错误。
我的代码是:
import pandas as pd
test_file = pd.read_csv("C:/Users/Lenovo/Desktop/testfile.csv")
test_select = test_file[["Category", "Shop"]]
print(test_select[1,1])
代码 print(test_select[1,1]) 应该显示第二列的第二行。
错误信息:
File "pandas_libs\hashtable_class_helper.pxi", line 1500, in pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: (1, 1)
During handling of the above exception, another exception occurred:
Traceback (most recent call last): File "C:/Users/Lenovo/.PyCharmCE2018.1/config/scratches/Dictionary.py", line 8, in print(h_select[1,1]) File "C:\Users\Lenovo\PycharmProjects\mindnotez\venv\lib\site-packages\pandas\core\frame.py", line 2688, in getitem return self._getitem_column(key) File "C:\Users\Lenovo\PycharmProjects\mindnotez\venv\lib\site-packages\pandas\core\frame.py", line 2695, in _getitem_column return self._get_item_cache(key) File "C:\Users\Lenovo\PycharmProjects\mindnotez\venv\lib\site-packages\pandas\core\generic.py", line 2489, in _get_item_cache values = self._data.get(item) File "C:\Users\Lenovo\PycharmProjects\mindnotez\venv\lib\site-packages\pandas\core\internals.py", line 4115, in get loc = self.items.get_loc(item) File "C:\Users\Lenovo\PycharmProjects\mindnotez\venv\lib\site-packages\pandas\core\indexes\base.py", line 3080, in get_loc return self._engine.get_loc(self._maybe_cast_indexer(key)) File "pandas_libs\index.pyx", line 140, in pandas._libs.index.IndexEngine.get_loc File "pandas_libs\index.pyx", line 162, in pandas._libs.index.IndexEngine.get_loc File "pandas_libs\hashtable_class_helper.pxi", line 1492, in pandas._libs.hashtable.PyObjectHashTable.get_item File "pandas_libs\hashtable_class_helper.pxi", line 1500, in pandas._libs.hashtable.PyObjectHashTable.get_item KeyError: (1, 1)
当我打印 print(test_select.head()) 时，我得到以下输出:
Category Shop
0 Jidlo Albert
1 Jidlo BILLA
2 Jidlo Albert
3 Jidlo Albert
4 Restaurant Kockafé Freyd
像 print(test_select[1:4]) 一样对数据框进行切片，打印第 1:3 行。 使用命令 print(test_select[1,1])，我想要第二列，第二行。但是，我收到上面的错误消息。
为什么我会收到 KeyError 异常？我错过了什么？
我使用:
- python 3.7
- PyCharm
- Anaconda(已安装)
请您参考如下方法:
当你想要切片数据帧时
按行号
df.iloc[[1, 5]] # to get rows 1 and 5
df.iloc[1:6] # to get rows 1 to 5 inclusive
您还可以将其缩小到特定列，如下所示(以避免 chain indexing )
df.iloc[[1, 5], df.columns.get_loc('Shop')]
或多列
df.iloc[[1, 5], df.columns.get_indexer(['Shop', 'Category'])]
基于标签的索引
# Numeric
df.loc[[1, 5]] # 1 and 5 are considered labels here
df.loc[[1, 5], 'Shop']
df.loc[[1, 5], ['Shop', 'Category']]
# Textual or otherwise
df.set_index('Shop', inplace=True)
df.loc[['BILLA', 'Albert'], 'Category']
