python - pandas 数据框中带有附加问题的时间序列

Question

我正在研究时间序列，我发现 pandas 数据框中有非常奇怪的行为

当索引不是时间序列时，以下代码有效

import pandas as pd
df = pd.DataFrame({"a":[1,2,3], "b":[31,41,51],"c":[31,52,23]}, index=["z", "y", "x"])
df1 = pd.DataFrame({"a":[41,55,16]}, index=["w", "v", "u"])
df2 = pd.DataFrame({"b":[24,3,57]}, index=["w", "v", "u"])
df3 = pd.DataFrame({"c":[111,153,123]}, index=["w", "v", "u"]) 
df = df.append(df1)
dfx.ix[df2.index, "b"] = df2

df 的输出:

    a   b   c
z   1  31  31
y   2  41  52
x   3  51  23
w  41  24 NaN
v  55   3 NaN
u  16  57 NaN

但是，当有 datetime64[ns] 索引或大小太大时，此方法不起作用

此外，当存在 datetime64[ns] 索引时，以下命令有效

df = df.append(df1)
df["b"][df2.index] = df2

为什么会这样？

Answer 1

您可以尝试fillna :

df = df.append(df1)
print df.fillna(df2)
    a   b   c
z   1  31  31
y   2  41  52
x   3  51  23
w  41  24 NaN
v  55   3 NaN
u  16  57 NaN

我使用 Datatimeindex 对其进行了测试，效果非常好:

import pandas as pd

df = pd.DataFrame({"a":[1,2,3], "b":[31,41,51],"c":[31,52,23]}, index=["z", "y", "x"])
df.index = pd.date_range('20160101',periods=3,freq='T')

df1 = pd.DataFrame({"a":[41,55,16]}, index=["w", "v", "u"])
df1.index = pd.date_range('20160104',periods=3,freq='T')

df2 = pd.DataFrame({"b":[24,3,57]}, index=["w", "v", "u"])
df2.index = pd.date_range('20160104',periods=3,freq='T')

df3 = pd.DataFrame({"c":[111,153,123]}, index=["w", "v", "u"])
df3.index = pd.date_range('20160104',periods=3,freq='T')

df = df.append(df1)
print df
                      a   b   c
2016-01-01 00:00:00   1  31  31
2016-01-01 00:01:00   2  41  52
2016-01-01 00:02:00   3  51  23
2016-01-04 00:00:00  41 NaN NaN
2016-01-04 00:01:00  55 NaN NaN
2016-01-04 00:02:00  16 NaN NaN

print df.fillna(df2)
                      a   b   c
2016-01-01 00:00:00   1  31  31
2016-01-01 00:01:00   2  41  52
2016-01-01 00:02:00   3  51  23
2016-01-04 00:00:00  41  24 NaN
2016-01-04 00:01:00  55   3 NaN
2016-01-04 00:02:00  16  57 NaN

df.ix[df2.index, "b"] = df2
print df
                      a   b   c
2016-01-01 00:00:00   1  31  31
2016-01-01 00:01:00   2  41  52
2016-01-01 00:02:00   3  51  23
2016-01-04 00:00:00  41  24 NaN
2016-01-04 00:01:00  55   3 NaN
2016-01-04 00:02:00  16  57 NaN