基于另一列的计算创建一列

Question

我想根据前一周的销售额创建另一个列。这是示例输入：

df = pd.DataFrame({'Week':[1,1,2,2,3,3,4,4,5,5,1,1,2,2,3,3,4,4,5,5],
                   'Category':['Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White'],
                   'id':[1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2],
                   'Sales':[100,200,300,400,100,200,300,400,100,200,100,200,300,400,100,200,300,400,100,200],
                  'Sales_others':[10,20,30,40,10,20,30,40,10,20,10,20,30,40,10,20,30,40,10,20]})
print(df)

基于此，我想创建另一个列，该列仅是前一周的销售额。这是所需输出的示例

    df_output = pd.DataFrame({'Week':[1,1,2,2,3,3,4,4,5,5,1,1,2,2,3,3,4,4,5,5],
                       'Category':['Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White','Red','White'],
                       'id':[1,1,1,1,1,1,1,1,1,1,2,2,2,2,2,2,2,2,2,2],
                       'Sales':[100,200,300,400,100,200,300,400,100,200,100,200,300,400,100,200,300,400,100,200],
                      'Sales_others':[10,20,30,40,10,20,30,40,10,20,10,20,30,40,10,20,30,40,10,20],
                      'Sales_previous_week':[0,0,100,200,300,400,100,200,300,400,0,0,100,200,300,400,100,200,300,400]})
print(df_output)

我发现很难创建自联接。前一周应该只受销售文件的影响，我应该能够保留“sales_others”列

--编辑 添加原始代码

CR_UK_NL_Weeklevel['PREVIOUS_WEEK'] = CR_UK_NL_Weeklevel.groupby(['RETAIL_SITE_ID','CATEGORY_NAME'])['CURRENT_WEEK'].shift(fill_value=0)
print(CR_UK_NL_Weeklevel)

重命名列

CR_UK_NL_Weeklevel.columns.values[4] = 'CURRENT_WEEK'
CR_UK_NL_Weeklevel.columns.values[3] = 'LAST_YEAR_WEEK'
CR_UK_NL_Weeklevel.columns.values

尝试实施解决方案：

CR_UK_NL_Weeklevel['PREVIOUS_WEEK'] = CR_UK_NL_Weeklevel.groupby(['RETAIL_SITE_ID','CATEGORY_NAME'])['CURRENT_WEEK'].shift(fill_value=0)
print(CR_UK_NL_Weeklevel)

[78]：

CR_UK_NL_Weeklevel['PREVIOUS_WEEK'] = CR_UK_NL_Weeklevel.groupby(['RETAIL_SITE_ID','CATEGORY_NAME'])['CURRENT_WEEK'].shift(fill_value=0)
print(CR_UK_NL_Weeklevel)

--错误

------------------------------------------ ------------------------------------------- KeyError Traceback（最近一次调用最后一次） 在 ----> 1 CR_UK_NL_Weeklevel['PREVIOUS_WEEK'] = CR_UK_NL_Weeklevel.groupby(['RETAIL_SITE_ID','CATEGORY_NAME'])['CURRENT_WEEK'].shift(fill_value=0) 2 打印（CR_UK_NL_Weeklevel） ~\AppData\Local\Continuum\anaconda3\lib\site-packages\pandas\core\base.py in getitem(self, key) 273 其他： 274 如果 key 不在 self.obj 中： --> 275 raise KeyError("Column not found: {key}".format(key=key)) 第276章 277 KeyError：'未找到列：CURRENT_WEEK'

Answer 1

如果每周和连续几周总是有相同的类别，请使用DataFrameGroupBy.shift 按Category 列分组：

df['Sales_PREVIOUS'] = df.groupby('Category')['Sales'].shift(fill_value=0)
print (df)
   Week Category  Sales  Sales_PREVIOUS
0     1      Red    100               0
1     1    White    200               0
2     2      Red    300             100
3     2    White    400             200
4     3      Red    100             300
5     3    White    200             400
6     4      Red    300             100
7     4    White    400             200
8     5      Red    100             300
9     5    White    200             400

旋转的另一个想法是使用DataFrame.pivot，然后使用DataFrame.shift 和DataFrame.stack 用于Series，最后通过DataFrame.join 添加新列：

s = df.pivot('Week','Category','Sales').shift(fill_value=0).stack()
df = df.join(s.rename('Sales_PREVIOUS WEEK'), on=['Week','Category'])

编辑：

使用新数据添加列id：

df['Sales_PREVIOUS'] = df.groupby(['id','Category'])['Sales'].shift(fill_value=0)

第二个解决方案：

s = df.set_index(['Week','id','Category'])['Sales'].unstack([1,2]).shift(fill_value=0).unstack()
df = df.join(s.rename('Sales_PREVIOUS WEEK'), on=['id','Category','Week'])
print (df)
    Week Category  id  Sales  Sales_others  Sales_PREVIOUS WEEK
0      1      Red   1    100            10                    0
1      1    White   1    200            20                    0
2      2      Red   1    300            30                  100
3      2    White   1    400            40                  200
4      3      Red   1    100            10                  300
5      3    White   1    200            20                  400
6      4      Red   1    300            30                  100
7      4    White   1    400            40                  200
8      5      Red   1    100            10                  300
9      5    White   1    200            20                  400
10     1      Red   2    100            10                    0
11     1    White   2    200            20                    0
12     2      Red   2    300            30                  100
13     2    White   2    400            40                  200
14     3      Red   2    100            10                  300
15     3    White   2    200            20                  400
16     4      Red   2    300            30                  100
17     4    White   2    400            40                  200
18     5      Red   2    100            10                  300
19     5    White   2    200            20                  400

编辑：

问题在于列名，使用：

cols = CR_UK_NL_Weeklevel.columns.tolist()
cols[4] = 'CURRENT_WEEK'
cols[3] = 'LAST_YEAR_WEEK'
CR_UK_NL_Weeklevel.columns = cols