python - 将数据实时附加到一个空的 pandas DataFrame

Question

我想实时向一个空的 DataFrame 添加一些数据:

import pandas as pd
import time

df = pd.DataFrame(columns=['time', 'price'])   # this is a simple example
                                               # but in my code, I have more 
                                               # columns: 'volume', etc.
for i in range(5):                             # here it lasts one day in my real use case
    time.sleep(2)
    t = pd.datetime.now()
    df[t] = 5 + i
    # here I need to have access to the latest updates of df

print df

输出是:

Empty DataFrame  
Columns: [time, price, 2015-12-27 01:55:29.812000, 2015-12-27 01:55:31.812000, 2015-12-27 01:55:33.812000, 2015-12-27 01:55:35.812000, 2015-12-27 01:55:37.812000]  
Index: []

而我想要:

time                                price
2015-12-27 01:55:29.812000          5
2015-12-27 01:55:31.812000          6
2015-12-27 01:55:33.812000          7
...

如何像这样将数据附加到 DataFrame？

Answer 1

考虑使用 pandas 的 append()将循环数据列表迁移到数据框的功能:

df = pd.DataFrame(columns=['time', 'price'])

for i in range(5):
    time.sleep(2)
    t = pd.datetime.now()
    df = df.append(pd.DataFrame({'time': [t],
                                 'price': [5 + i]}))
print df