pd.Timedelta在数据帧列上的转换

Question

I am trying to convert a dataframe column to a timedelta but am having issues. The format that the column comes in looks like '+XX:XX:XX' or '-XX:XX:XX'

My dataframe:

    df = pd.DataFrame({'time':['+06:00:00', '-04:00:00'],})

My approach:

    df['time'] = pd.Timedelta(df['time'])

However, I get the error:

    ValueError: Value must be Timedelta, string, integer, float, timedelta or convertible

When I do a simpler example:

    time = pd.Timedelta('+06:00:00')

I get my desired output:

    Timedelta('0 days 06:00:00')

What would be the approach if I wanted to convert a series into a timedelta with my desired output?

Answer 1

I would strongly recommend to use specifically designed and vectorized (ie very fast) method: to_timedelta() :

In [40]: pd.to_timedelta(df['time'])
Out[40]:
0            06:00:00
1   -1 days +20:00:00
Name: time, dtype: timedelta64[ns]

Timing against a 200K rows DF:

In [41]: df = pd.concat([df] * 10**5, ignore_index=True)

In [42]: df.shape
Out[42]: (200000, 1)

In [43]: %timeit pd.to_timedelta(df['time'])
1 loop, best of 3: 891 ms per loop

In [44]: %timeit df['time'].apply(pd.Timedelta)
1 loop, best of 3: 7.15 s per loop

In [45]: %timeit [pd.Timedelta(x) for x in df['time']]
1 loop, best of 3: 5.52 s per loop

Answer 2

The error is pretty clear:

ValueError: Value must be Timedelta, string, integer, float, timedelta or convertible

What you are passing to pd.Timedelta() is none of the above data types:

>>> type(df['time'])
<class 'pandas.core.series.Series'>

Probably what you want it:

>>> [pd.Timedelta(x) for x in df['time']]
[Timedelta('0 days 06:00:00'), Timedelta('-1 days +20:00:00')]

Or:

>>> df['time'].apply(pd.Timedelta)
0            06:00:00
1   -1 days +20:00:00
Name: time, dtype: timedelta64[ns]

See more examples in the docs .