How to extract specific dates from a datetime table?

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Ashfaq Ahmed
Ashfaq Ahmed 2023-4-19
回答： Eric Sofen 2023-4-20
Hi!
I have a datetime table (DATE1.mat) containing some dates from 1984 to 2022 at 10:00 am. I have another date timetable (DATE2.mat) that contains data from 2005 to 2019 at 10:00 am with temperature values. Can anyone please tell me how to find only the dates from DATE2.mat file that belong to DATE1.mat list?
Any feedback will be greatly appreciated!

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采纳的回答

Les Beckham
Les Beckham 2023-4-19
Ran in:
whos('-file', 'DATE1.mat')
Name Size Bytes Class Attributes datet - 6112 datetime
whos('-file', 'DATE2.mat')
Name Size Bytes Class Attributes B - 83241 timetable
load('DATE1.mat')
load('DATE2.mat')
whos
Name Size Bytes Class Attributes B 5141x1 83241 timetable ans 1x34 68 char cmdout 1x33 66 char datet 764x1 6112 datetime
head(datet)
02-May-1984 10:00:00 03-Jun-1984 10:00:00 19-Jun-1984 10:00:00 23-Sep-1984 10:00:00 09-Oct-1984 10:00:00 25-Oct-1984 10:00:00 10-Nov-1984 10:00:00 26-Nov-1984 10:00:00
head(B)
Time Temp ____________________ ____ 01-Jan-2005 10:00:00 4.98 02-Jan-2005 10:00:00 4.44 03-Jan-2005 10:00:00 5.33 04-Jan-2005 10:00:00 5.09 05-Jan-2005 10:00:00 4.81 06-Jan-2005 10:00:00 4.1 07-Jan-2005 10:00:00 4.51 08-Jan-2005 10:00:00 5.09
found_date_idx = ismember(datet, B.Time); % logical indexes for dates in datet that are found in B
B_selected = B(found_date_idx, :) % extract the rows from B that match the found dates
B_selected = 278×1 timetable
Time Temp ____________________ ____ 02-Feb-2006 10:00:00 5.58 03-Feb-2006 10:00:00 5.39 04-Feb-2006 10:00:00 5.44 05-Feb-2006 10:00:00 5.92 06-Feb-2006 10:00:00 5.54 07-Feb-2006 10:00:00 5.26 08-Feb-2006 10:00:00 4.96 09-Feb-2006 10:00:00 3.7 10-Feb-2006 10:00:00 3.69 11-Feb-2006 10:00:00 3.55 12-Feb-2006 10:00:00 3.21 13-Feb-2006 10:00:00 3.93 14-Feb-2006 10:00:00 4.74 15-Feb-2006 10:00:00 4.87 16-Feb-2006 10:00:00 4.73 17-Feb-2006 10:00:00 5.69

更多回答（2 个）

Eric Sofen
Eric Sofen 2023-4-20
Ran in:
If you know all the datetimes have 10:00:00 time components and you're just matching dates, timetable subscripting does that directly. Of course, if you're concerned about wanting non-exact matches (e.g. to match things that occur on the same date but not the same time), then the approach suggested by Adam is helpful. Other approaches for dealing with inexact matches may involve retime, timerange, or withtol.
load DATE1.mat
load DATE2.mat
B(datet,:)
ans = 278×1 timetable
Time Temp ____________________ _____ 20-Jan-2005 10:00:00 2.75 28-Jan-2005 10:00:00 -0.19 05-Feb-2005 10:00:00 0.82 13-Feb-2005 10:00:00 1.87 09-Mar-2005 10:00:00 1.96 17-Mar-2005 10:00:00 1.98 10-Apr-2005 10:00:00 7.89 18-Apr-2005 10:00:00 8.65 26-Apr-2005 10:00:00 7.94 12-May-2005 10:00:00 10.31 28-May-2005 10:00:00 10.95 05-Jun-2005 10:00:00 14.26 15-Jul-2005 10:00:00 19.78 23-Jul-2005 10:00:00 20.32 08-Aug-2005 10:00:00 20.72 16-Aug-2005 10:00:00 23.2
Adam Danz
Adam Danz 2023-4-19
Datetimes are rounded down to the start of the day using dateshift. Then, ismember finds matches between the two sets of dates.
load DATE1.mat % datet (vector)
load DATE2.mat % B (table)
[isDateMatch, idx] = ismember(dateshift(datet,'start','day'),dateshift(B.Time,'start','day'));
B.Time(idx(isDateMatch)) corresponds with datet(isDateMatch)
This line verifies that they are equal.
isequal(dateshift(B.Time(idx(isDateMatch)),'start','day') , dateshift(datet(isDateMatch),'start','day'))

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