# How do to get a specific time from datetime format in Matlab?

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Kofial on 11 Nov 2020
Commented: Kofial on 12 Nov 2020
I have these data:
x=(17-Apr-2020 06:59:00,17-Apr-2020 07:00:00,17-Apr-2020 07:01:00,17-Apr-2020,07:02:0017-Apr-2020,07:03:00)
y=(06:58:30,17-Apr-2020 06:59:30,17-Apr-2020 07:00:30,17-Apr-2020 07:01:30,17-Apr-2020 07:02:30,17-Apr-2020 07:03:30)
Both times (x,y) are in the datetime format).
To get the time for x from 07:00:00 till the end I do this:
interpolation_time = (x(420):minutes(1):x(end));
For y I need it from 07:00:30 till the end. How can I do it? It has a different timestamp.
Thank you!
Kofial on 12 Nov 2020
It works very well. Thank you

Walter Roberson on 11 Nov 2020
Edited: Walter Roberson on 11 Nov 2020
[xh, xm, xs] = hms(x);
xidx = find(xh >= 7 & xm >= 0, 1);
[yh, ym, ys] = hms(y);
yidx = find(yh >= 7 & ym >= 0 & ys >= 30, 1);
selected_x = x(xidx:end);
selected_y = y(yidx:end);
Note here that this code is perfectly happy if the dates do not match at all, and if the entries are out of order. Your problem definition involved finding the first entry that meets a particular time-based criteria that ignores dates.
Perhaps you should use isbetween() ?
xbase = dateshift(x(1), 'start', 'day');
dx = x - xbase;
dy = y - xbase;
masky = dy >= hours(7) + seconds(30);
Steven Lord on 11 Nov 2020
You can compute dx and dy without computing xbase using the timeofday function for datetime arrays.
dt = datetime('now') + hours(48*randn(10, 1)) + minutes(60*randn(10, 1));
td = timeofday(dt);
results = table(dt, td, 'VariableNames', ["Date and time", "Time since midnight"])
results = 10x2 table
Date and time time since midnight ____________________ ___________________ 09-Nov-2020 07:06:30 07:06:30 10-Nov-2020 16:46:13 16:46:13 09-Nov-2020 20:24:50 20:24:50 12-Nov-2020 20:58:31 20:58:31 10-Nov-2020 09:09:45 09:09:45 09-Nov-2020 02:58:16 02:58:16 13-Nov-2020 12:14:36 12:14:36 11-Nov-2020 13:15:02 13:15:02 12-Nov-2020 01:21:48 01:21:48 09-Nov-2020 12:10:02 12:10:02