# how to plot double against datetime

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Sirius8 on 17 Apr 2021
Commented: Sirius8 on 17 Apr 2021
I am trying to plot a .csv file.
filename='data.csv';
time = data{:,1}+data{:,2};
X = data{:,3};
Y = data{:,4};
Z = data{:,5};
plot(X) % OK
plot(time,X) % NOT OK
When I plot X i get the figure that i want (see 1), but when I plot X against time, I get figure 2. Any ideas why this is happening and how to plot X against time and have the figure look like fig.1 with time in x axis?

Clayton Gotberg on 17 Apr 2021
Edited: Clayton Gotberg on 17 Apr 2021
In the attached CSV, the time data is the same for every 100 columns or so. Because of this, MATLAB is plotting all of the events that happened at that time at the same position on the x-axis. You will not be able to use the time information in the csv for plotting because the time is only measured to the second but you are taking measurements hundreds of times per second.
If you want to plot vs. time, you will need to create a new time vector.
time_new = linspace(start_time,end_time,size(X,1));
%start_time is the earliest time in the sequence
will create equally spaced points in time to plot X against. Note that if you started or stopped measuring in the middle of a second, the points will not match up with the true time exactly if you start or stop from the recorded value:
true_time = [0.5 0.75 1 1.25 1.5 1.75 2 2.25];
time_new = [0 0.2857 0.5714 0.8571 1.1429 1.4286 1.7143 2];
If the data samples you took are not equally spaced in time, you will need to re-measure your data with a more accurate clock.
Sirius8 on 17 Apr 2021
Thank you!