[英]Creating new column in a Pandas df, where each row's value depends on the value of a different column in the row immediately above it
假設以下 Pandas df:
# Import dependency.
import pandas as pd
# Create data for df.
data = {'Value': [1000, 1020, 1011, 1010, 1030, 950, 1001, 1100, 1121, 1131],
'Dummy_Variable': [0,0,1,0,0,0,1,0,1,1]
}
# Create DataFrame
df = pd.DataFrame(data)
display(df)
我想在 df 中添加一個名為“Placeholder”的新列。 Placeholder 的值將基於基於以下規則的“Dummy_Variable”列:
所需的結果是一個帶有新“占位符”列的 df,它看起來像通過運行以下代碼生成的 df:
desired_data = {'Value': [1000, 1020, 1011, 1010, 1030, 950, 1001, 1100, 1121, 1131],
'Dummy_Variable': [0,0,1,0,0,0,1,0,1,1],
'Placeholder': [1000,1020,1011,1011,1011,1011,1001,1001,1121,1131]}
df1 = pd.DataFrame(desired_data)
display(df1)
我可以在 Excel 中輕松地做到這一點,但我無法弄清楚如何在 Pandas 中不使用循環來做到這一點。 任何幫助是極大的贊賞。 謝謝!
您可以為此使用np.where :
import pandas as pd
import numpy as np
data = {'Value': [1000, 1020, 1011, 1010, 1030, 950, 1001, 1100, 1121, 1131],
'Dummy_Variable': [0,0,1,0,0,0,1,0,1,1]
}
df = pd.DataFrame(data)
df['Placeholder'] = np.where((df.Dummy_Variable.cumsum() == 0) | (df.Dummy_Variable == 1), df.Value, np.nan)
# now forward fill the remaining NaNs
df['Placeholder'].fillna(method='ffill', inplace=True)
df
Value Dummy_Variable Placeholder
0 1000 0 1000.0
1 1020 0 1020.0
2 1011 1 1011.0
3 1010 0 1011.0
4 1030 0 1011.0
5 950 0 1011.0
6 1001 1 1001.0
7 1100 0 1001.0
8 1121 1 1121.0
9 1131 1 1131.0
# check output:
desired_data = {'Value': [1000, 1020, 1011, 1010, 1030, 950, 1001, 1100, 1121, 1131],
'Dummy_Variable': [0,0,1,0,0,0,1,0,1,1],
'Placeholder': [1000,1020,1011,1011,1011,1011,1001,1001,1121,1131]}
df1 = pd.DataFrame(desired_data)
check = df['Placeholder'] == df1['Placeholder']
check.sum()==len(df1)
# True
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.