python - 如何根据同一行中另一列中的值向前填充列值

Question

我想根据次数列转发填写金额列。例如第一个值是 2800000.0 ，我希望这个值被填充6次。

amount      times       
2800000.0    6
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0   
4750000.0    4         
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0   
nan     0    0    

期望的输出:

amount      times       
2800000.0    6
2800000.0    0   
2800000.0    0   
2800000.0    0   
2800000.0    0   
2800000.0    0   
2800000.0    0   
4750000.0    4         
4750000.0    0   
4750000.0    0   
4750000.0    0   
4750000.0    0   
nan     0    0   
nan     0    0   

Answer 1

首先通过使用累积和测试非缺失值来创建组并传递给 GroupBy.apply带有 lambda 函数 Series.ffill每组的第一个值次受到限制:

#if necessary convert strings t onumeric and NaNs
#df['amount'] = pd.to_numeric(df['amount'], errors='coerce')

print (df['amount'].dtype)
float64

g = df['amount'].notna().cumsum()

f = lambda x: x['amount'].ffill(limit=x['times'].iat[0])
df['amount'] = df.groupby(g, group_keys=False).apply(f)
print (df)
       amount  times
0   2800000.0      6
1   2800000.0      0
2   2800000.0      0
3   2800000.0      0
4   2800000.0      0
5   2800000.0      0
6   2800000.0      0
7   4750000.0      4
8   4750000.0      0
9   4750000.0      0
10  4750000.0      0
11  4750000.0      0
12        NaN      0
13        NaN      0