Can you Group XArray Data Array by Day of Month?-CodePudding

If there was a variable in an xarray dataset with a time dimension with daily values over some multiyear time span

2017-01-01 ... 2018-12-31, then it is possible to group the data by month, or by the day of the year, using

.groupby("time.month") or .groupby("time.dayofyear")

Is there a way to efficiently group the data by the day of the month, for example if I wanted to calculate the mean value on the 21st of each month?

CodePudding user response：

See the xarray docs on the DateTimeAccessor helper object. For more info, you can also check out the xarray docs on Working with Time Series Data: Datetime Components, which in turn refers to the pandas docs on date/time components.

You're looking for day. Unfortunately, both pandas and xarray simply describe .dt.day as referring to "the days of the datetime" which isn't particularly helpful. But if you take a look at python's native datetime.Date.day definition, you'll see the more specific:

date.day
Between 1 and the number of days in the given month of the given year.

So, simply

da.groupby("time.day")

Should do the trick!

CodePudding user response：

I not sure, but maybe you can do like this:

import datetime

x = datetime.datetime.now()

day = x.strftime("%d")
month = x.strftime("%m")
year = x.strftime("%Y")

.groupby(month) or .groupby(year)