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[英]apply function on subset of dataframe rows in column based on value in other column
[英]Apply function to dataframe based on column with other dataframe based on index
我想根據它們的顏色對列蘋果的值執行一些操作(例如x*apples^y
)。 相應的值位於單獨的數據框中:
import pandas as pd
import numpy as np
df1 = pd.DataFrame({'apples': [2, 1, 5, 6, 7], 'color': [1, 1, 1, 2, 2]})
df2 = pd.DataFrame({'x': [100, 200], 'y': [0.5, 0.3]}).set_index(np.array([1, 2]), 'color')
我正在尋找以下結果:
apples color
0 100*2^0.5 1
1 100*1^0.5 1
2 100*5^0.5 1
3 200*6^0.3 2
4 200*7^0.3 2
首先將DataFrame.join
與默認左連接一起使用,然后使用附加列進行操作:
df = df1.join(df2, on='color')
df['apples'] = df['x'] * df['apples'] ** df['y']
print (df)
apples color x y
0 141.421356 1 100 0.5
1 100.000000 1 100 0.5
2 223.606798 1 100 0.5
3 342.353972 2 200 0.3
4 358.557993 2 200 0.3
有左連接,因此附加到df1
新列應該可以工作:
df = df1.join(df2, on='color')
df1['apples'] = df['x'] * df['apples'] ** df['y']
print (df1)
apples color
0 141.421356 1
1 100.000000 1
2 223.606798 1
3 342.353972 2
4 358.557993 2
另一個想法是使用雙map
:
df1['apples'] = df1['color'].map(df2['x']) * df1['apples'] ** df1['color'].map(df2['y'])
print (df1)
apples color
0 141.421356 1
1 100.000000 1
2 223.606798 1
3 342.353972 2
4 358.557993 2
我認為你需要pandas.merge -
temp = df1.merge(df2, left_on='color', right_index= True, how='left')
df1['apples'] = (temp['x']*(temp['apples'].pow(temp['y'])))
輸出
apples color
0 141.421356 1
1 100.000000 1
2 223.606798 1
3 342.353972 2
4 358.557993 2
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