[英]Count unique dates in pandas dataframe
I have a dataframe of surface weather observations ( fzraHrObs
) organized by a station identifier code and date. 我有一个按台站标识符代码和日期组织的地面天气观测(
fzraHrObs
)数据fzraHrObs
。 fzraHrObs
has several columns of weather data. fzraHrObs
具有几列天气数据。 The station code and date (datetime objects) look like: 站点代码和日期(datetime对象)如下所示:
usaf dat
716270 2014-11-23 12:00:00
2015-12-20 08:00:00
2015-12-20 09:00:00
2015-12-21 04:00:00
2015-12-28 03:00:00
716280 2015-12-19 08:00:00
2015-12-19 08:00:00
I would like to get a count of the number of unique dates (days) per year for each station - ie the number of days of obs per year at each station. 我想获得每个站点每年唯一日期(天)的数量的计数,即每个站点每年obs的天数。 In my example above this would give me:
在上面的示例中,这将给我:
usaf Year Count
716270 2014 1
2015 3
716280 2014 0
2015 1
I've tried using groupby and grouping by station, year, and date: grouped = fzraHrObs['dat'].groupby(fzraHrObs['usaf'], fzraHrObs.dat.dt.year, fzraHrObs.dat.dt.date])
我试过使用groupby并按站点,年份和日期
grouped = fzraHrObs['dat'].groupby(fzraHrObs['usaf'], fzraHrObs.dat.dt.year, fzraHrObs.dat.dt.date])
: grouped = fzraHrObs['dat'].groupby(fzraHrObs['usaf'], fzraHrObs.dat.dt.year, fzraHrObs.dat.dt.date])
Count, size, nunique, etc. on this just gives me the number of obs on each date, not the number of dates themselves per year. 计数,大小,唯一性等等都给了我每个日期的obs数,而不是每年的日期数。 Any suggestions on getting what I want here?
在这里得到我想要的任何建议吗?
Could be something like this, group the date by usaf
and year
and then count the number of unique values: 可能是这样,将日期按
usaf
和year
usaf
,然后计算唯一值的数量:
import pandas as pd
df.dat.apply(lambda dt: dt.date()).groupby([df.usaf, df.dat.apply(lambda dt: dt.year)]).nunique()
# usaf dat
# 716270 2014 1
# 2015 3
# 716280 2015 1
# Name: dat, dtype: int64
The following should work: 以下应该工作:
df.groupby(['usaf', df.dat.dt.year])['dat'].apply(lambda s: s.dt.date.nunique())
What I did differently is group by two levels only, then use the nunique
method of pandas series to count the number of unique dates in each group. 我做的不同的是仅按两个级别进行分组,然后使用pandas系列的
nunique
方法计算每个组中唯一日期的数量。
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