就地修改 DataFrame 中的列

Question

编辑：我已经意识到，当使用 .loc 访问时，我没有收到任何错误，而是一个警告，所以代码确实有效。

我有一个需要清理的数据集。我需要做的一件事是删除所有超过 50000kn 的交易。 碰巧成本bruto_prihod 是字符串格式，事务transakcija_sifra 跨越多行。 另一个不便之处是十进制格式使用逗号（我们在克罗地亚语中使用十进制逗号）而不是点。

这是我在任务之前的代码：

    import pandas as pd
    import numpy as np

    diversus = pd.read_csv(r"C:\Users\dagejev\Desktop\excel\diversus4_saved.csv", encoding="cp1252", sep=";")

    df = diversus.copy()

    df_filter = df[(df['faza'] == 'A') &
                   ( (df['grupa_id'] == 'W ODIJELO') | (df['grupa_id'] == 'ODIJELO') ) &
                   ( (df['vp_kupac_id']!= 591) & (df['vp_kupac_id']!= 333) & (df['vp_kupac_id']!= 332) ) &
                   ( (df['brand_naziv'] == 'JOOP') | (df['brand_naziv'] == 'JOOP!') ) &
                   (df['vrsta_robe']=='ROBA') &
                   (df['divizija'] == 'MEN')]
    print('df: ', len(df), 'filtered: ', len(df_filter))

以下是相关部分：

#This is what I tried first

df_filter['bruto_prihod'] = df_filter['bruto_prihod'].str.replace(',','.')

但是，它不起作用：

C:\Users\dagejev\AppData\Local\Continuum\anaconda3\lib\site-packages\ipykernel_launcher.py:1: SettingWithCopyWarning: 
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
  """Entry point for launching an IPython kernel.

建议的替代方案也没有：

    df_filter[:,'bruto_prihod'] = df_filter['bruto_prihod'].str.replace(',','.')

    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    <ipython-input-82-0e27bdc0e78f> in <module>
    ----> 1 df_filter[:,'bruto_prihod'] = df_filter['bruto_prihod'].str.replace(',','.')

    ~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\frame.py in __setitem__(self, key, value)
       3368         else:
       3369             # set column
    -> 3370             self._set_item(key, value)
       3371 
       3372     def _setitem_slice(self, key, value):

    ~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\frame.py in _set_item(self, key, value)
       3443 
       3444         self._ensure_valid_index(value)
    -> 3445         value = self._sanitize_column(key, value)
       3446         NDFrame._set_item(self, key, value)
       3447 

    ~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\frame.py in _sanitize_column(self, key, value, broadcast)
       3659 
       3660         # broadcast across multiple columns if necessary
    -> 3661         if broadcast and key in self.columns and value.ndim == 1:
       3662             if (not self.columns.is_unique or
       3663                     isinstance(self.columns, MultiIndex)):

    ~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\indexes\base.py in __contains__(self, key)
       3918     @Appender(_index_shared_docs['contains'] % _index_doc_kwargs)
       3919     def __contains__(self, key):
    -> 3920         hash(key)
       3921         try:
       3922             return key in self._engine

    TypeError: unhashable type: 'slice'

但是这个链索引确实 (which is supposedly always bad to use)：

    df_filter[:]['bruto_prihod'] = df_filter['bruto_prihod'].str.replace(',','.')

此外，这不起作用：

    df_filter['bruto_prihod'] = pd.to_numeric(df_filter['bruto_prihod'])

但这确实：

df_filter[:]['bruto_prihod'] = pd.to_numeric(df_filter['bruto_prihod'])

为什么会这样？ 为什么我必须为我的就地分配工作链接索引？

另外，如果有人感兴趣，这就是我对交易进行分组的方式：

df_filter.groupby('transakcija_sifra').agg({'bruto_prihod':np.sum}).sort_values('bruto_prihod', ascending=False)

Answer 1

为了避免警告，您可以使用明确的copy：

df_filter = df[(df['faza'] == 'A') &
               ( (df['grupa_id'] == 'W ODIJELO') | (df['grupa_id'] == 'ODIJELO') ) &
               ( (df['vp_kupac_id']!= 591) & (df['vp_kupac_id']!= 333) & (df['vp_kupac_id']!= 332) ) &
               ( (df['brand_naziv'] == 'JOOP') | (df['brand_naziv'] == 'JOOP!') ) &
               (df['vrsta_robe']=='ROBA') &
               (df['divizija'] == 'MEN')].copy()