analyzing time

Terry Reedy tjreedy at
Fri Jul 5 21:54:46 CEST 2013

On 7/5/2013 3:18 PM, noydb wrote:

> I have a table with a column of type date, with dates and time

This is a datetime in Python parlance.

> combined (like '1/6/2013 3:52:69PM'), that spans many months.  How
> would I pull out records that are the first and last entries per
> day?

Sort on that column. Look at pairs of rows. If the days differ, you have 
the last of the first and the first of the second. One way:

it = <table iterator>
dt1 = next(it)
d1 = date(dt1)  # whatever that looks like

for row in it:
   dt2 = row
   d2 = date(dt2)
   if d1 != d2:
     do_whatever(dt1, dt2)
   dt1, d1 = dt2, d2

> Also, if I wanted to find time clusters per day (or per week) -- like
> if an entry is made every day around 11am -- is there a way to get at
> that temporal statistical cluster?

Make a histogram of time, ignoring date.

> Python 2.7, Windows 7.
> Any guidance would be greatly appreciated!  Time seems tricky...


Terry Jan Reedy

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