使用<和>在Pandas中选择日期范围时遇到麻烦

Question

a really simple question perhaps, but it's my first time working with pandas already and I'm having trouble slicing up my dataframes into smaller ones based on dates.

So, i have a dataframe (named firstreadin ) that looks like this (and thousands more rows):

        date               numbers  megaball
0 1999-01-12     [5, 7, 9, 20, 46]         2
1 1999-01-08   [5, 21, 23, 26, 37]         3
2 1999-01-05   [4, 31, 32, 34, 43]        19
3 1999-01-01  [11, 19, 28, 43, 48]         5
4 1998-12-29     [3, 5, 7, 28, 35]        10

and i want to slice them into a couple periods given specific date dividers, and while I'm having no trouble specifying the first and last periods, i can't seem to specify the middle periods:

#firsttime and secondtime are the date separators
firsttime = datetime.datetime.strptime('1/13/99', '%m/%d/%y')
secondtime = datetime.datetime.strptime('5/15/02', '%m/%d/%y')

firstperiod = firstreadin[firstreadin.date < firsttime].reset_index(drop=True)
thirdperiod = firstreadin[firstreadin.date > secondtime].reset_index(drop=True)

i can't get the secondperiod! (the one between firsttime and secondtime). I've tried this:

secondperiod = firstreadin[firstreadin.date >= firsttime and firstreadin.date < secondtime] 

but this just gives me ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all(). ValueError: The truth value of a Series is ambiguous. Use a.empty, a.bool(), a.item(), a.any() or a.all().

What's going on and how should I solve it? Thanks!

Answer 1

You can use numpy.logical_and : numpy.logical_and(a, b)

    secondperiod = firstreadin[numpy.logical_and(firstreadin.date >= firsttime, firstreadin.date < secondtime)]

I hope this can help you!