如何向下填充（向前填充）pandas 中過濾的 dataframe 列

Question

問題陳述：需要填寫過濾后的 dataframe。

我有一個很大的 dataframe。這里沒有顯示，但我在下面包含了一個虛擬 dataframe 作為示例。
我想要的唯一 Status/State 組合是 UP/GOOD 和 DOWN/BAD。
我的數據集目前有不需要的 DOWN/GOOD 組合，我正在嘗試通過填寫過濾后的 dataframe 將其更正為 DOWN/BAD。請就下面的代碼提出建議，它不起作用。 這個問題有幾個其他的解決方案，但我想要 filldown (.ffill) 方法。

謝謝！

未經過濾的數據集

過濾后的數據集：顯示關閉狀態

所需的解決方案

代碼：

"""This is a dummy dataframe"""
import pandas as pd
import numpy as np
dummydata=[["Up","Good"],["Up","Good"],["Up","Good"],["Down","Bad"],["Up","Good"],
           ["Down","Good"],["Down","Good"],["Down","Good"],["Up","Good"],["Up","Good"],
           ["Down","Bad"],["Up","Good"],["Up","Good"],["Up","Good"],["Up","Good"]]
df=pd.DataFrame(dummydata, columns=['Status','State'])
filt=df['Status']=="Down"
df2=df.loc[filt]
df2.loc[df2['State']=='Good','State']=""
df2.loc[df2.State=='','State']= np.nan
df2.loc[df2['State']=='','State']=df2['State'].ffill()
print(df,df2)

我當前的填充方法不起作用。 提供代碼。 任何幫助將不勝感激

Answer 1

這里不需要切片。

最簡單的方法是：

df2['State'] = df2['State'].replace('Good', np.nan).ffill()

Output：

   Status State
3    Down   Bad
5    Down   Bad
6    Down   Bad
7    Down   Bad
10   Down   Bad

Answer 2

用這個：

df.loc[df['Status']=='Down','State']='Bad'
df[df['Status']=='Down']

   Status State
3    Down   Bad
5    Down   Bad
6    Down   Bad
7    Down   Bad
10   Down   Bad

Answer 3

您可以使用條件直接過濾它們並分配它們。

代碼：

import pandas as pd
import numpy as np
dummydata=[["Up","Good"],["Up","Good"],["Up","Good"],["Down","Bad"],["Up","Good"],
        ["Down","Good"],["Down","Good"],["Down","Good"],["Up","Good"],["Up","Good"],
        ["Down","Bad"],["Up","Good"],["Up","Good"],["Up","Good"],["Up","Good"]]
df=pd.DataFrame(dummydata, columns=['Status','State'])
#Filter Status == Down and State == Good
df.loc[((df["Status"] == "Down") &  (df["State"] =="Good")), "State"] = "Bad"