compare datetime with different lengths

I have two datetime variables: dt_D and dt_C. They cover the same set of time but dt_C is significantly shorter becuase it is missing timesteps.

I would like to plot two other variables, D & C, (which are the same length as their respective datetimes) when they both have data at the same timestep. I do not want to do any interpolation, just simply plot the variables when they overlap. Another alternative would be to remove timesteps from dt_D when they do not exist in dt_C.

Is there an easy way to do this?

Answer 1

[Ameer Hamza]

There can be several ways to do this. For example, see interp1() or retime().

This code shows an example

t1 = datetime(2020,1,1):datetime(2020,1,20);
y1 = rand(size(t1));

t2 = datetime(2020,1,1):days(4):datetime(2020,1,20);
y2 = rand(size(t2));

y2_t1 = interp1(t2, y2, t1, 'linear', 'extrap');

figure()
axes();
hold on;
plot(t1, y1);
plot(t1, y2_t1);

[SW]

Thanks for your response. I do not want to do any interpolation though, rather I would just like to isolate the variables when they have overlapping timesteps.

[Ameer Hamza]

If you just want common elements then you can try intersect()

t1 = datetime(2020,1,1):datetime(2020,1,20);
y1 = rand(size(t1));
t2 = datetime(2020,1,1):days(4):datetime(2020,1,20);
y2 = rand(size(t2));

[t_new, idx1, idx2] = intersect(t1, t2);

y1_new = y1(idx1);
y2_new = y2(idx2);

figure()
axes();
hold on;
plot(t_new, y1_new);
plot(t_new, y2_new);

Answer 2

[Peter Perkins]

SW, if all you want is a plot, there's nothing special you need to do, just plot them.

t1 = datetime(2020,11,19) + caldays(0:2:10)';
y1 = rand(size(t1));
t2 = datetime(2020,11,17) + caldays(0:15)';
y2 = rand(size(t2));

plot(t1,y1,'-o');
hold on;
plot(t2,y2,'-x');
hold off

If you really do want to up/downsample, put them in a timetable and use synchronize. It's a one-liner, and very easy to do other similar things like interpolation or whatever.

>> tt1 = timetable(t1,y1);
>> tt2 = timetable(t2,y2);
>> tt12 = synchronize(tt1,tt2,'intersect')
tt12 =
  6×2 timetable
        t1            y1          y2   
    ___________    ________    ________
    19-Nov-2020     0.13612    0.012766
    21-Nov-2020     0.79886     0.92698
    23-Nov-2020    0.007788     0.78629
    25-Nov-2020     0.85174     0.31578
    27-Nov-2020     0.10331    0.053424
    29-Nov-2020      0.5331     0.59552