Python Pandas -- 用前一列的值向前填充整行

Question

pandas 开发新手。如何使用先前看到的一列中包含的值转发填充 DataFrame？

独立示例：

import pandas as pd
import numpy as np
O = [1, np.nan, 5, np.nan]
H = [5, np.nan, 5, np.nan]
L = [1, np.nan, 2, np.nan]
C = [5, np.nan, 2, np.nan]
timestamps = ["2017-07-23 03:13:00", "2017-07-23 03:14:00", "2017-07-23 03:15:00", "2017-07-23 03:16:00"]
dict = {'Open': O, 'High': H, 'Low': L, 'Close': C}
df = pd.DataFrame(index=timestamps, data=dict)
ohlc = df[['Open', 'High', 'Low', 'Close']]

这会产生以下 DataFrame：

print(ohlc)
                     Open  High  Low  Close
2017-07-23 03:13:00   1.0   5.0  1.0    5.0
2017-07-23 03:14:00   NaN   NaN  NaN    NaN
2017-07-23 03:15:00   5.0   5.0  2.0    2.0
2017-07-23 03:16:00   NaN   NaN  NaN    NaN

我想从最后一个 DataFrame 变成这样：

                     Open  High  Low  Close
2017-07-23 03:13:00   1.0   5.0  1.0    5.0
2017-07-23 03:14:00   5.0   5.0  5.0    5.0
2017-07-23 03:15:00   5.0   5.0  2.0    2.0
2017-07-23 03:16:00   2.0   2.0  2.0    2.0

因此 'Close' 中先前看到的值向前填充整行，直到看到一个新的填充行。像这样填充列 'Close' 很简单：

column2fill = 'Close'
ohlc[column2fill] = ohlc[column2fill].ffill()
print(ohlc)
                     Open  High  Low  Close
2017-07-23 03:13:00   1.0   5.0  1.0    5.0
2017-07-23 03:14:00   NaN   NaN  NaN    5.0
2017-07-23 03:15:00   5.0   5.0  2.0    2.0
2017-07-23 03:16:00   NaN   NaN  NaN    2.0

但是有没有办法用这些行的 'Close' 值填充 03:14:00 和 03:16:00 行？有没有一种方法可以使用一个正向填充一步完成，而不是先填充 'Close' 列？

Answer 1

看来您需要 assign 和 ffill，然后 bfill 每行 axis=1，但需要完整的 NaN 行：

df = ohlc.assign(Close=ohlc['Close'].ffill()).bfill(axis=1)
print (df)
                     Open  High  Low  Close
2017-07-23 03:13:00   1.0   5.0  1.0    5.0
2017-07-23 03:14:00   5.0   5.0  5.0    5.0
2017-07-23 03:15:00   5.0   5.0  2.0    2.0
2017-07-23 03:16:00   2.0   2.0  2.0    2.0

什么相同：

ohlc['Close'] = ohlc['Close'].ffill()
df = ohlc.bfill(axis=1)
print (df)
                     Open  High  Low  Close
2017-07-23 03:13:00   1.0   5.0  1.0    5.0
2017-07-23 03:14:00   5.0   5.0  5.0    5.0
2017-07-23 03:15:00   5.0   5.0  2.0    2.0
2017-07-23 03:16:00   2.0   2.0  2.0    2.0

Python Pandas -- 用前一列的值向前填充整行

Python Pandas -- Forward filling entire rows with value of one previous column

python

dataframe

pandas

data-cleaning

data-science