convert from datetimes to double

I have created a variable called P_D and I want to put into it a date time asociated with each row (its financial data)

P_D(i,1)=data.Dates(i);
P_D(i,2)=data.Close(i);
P_D(i,3)=Premium;

When I run the code it is saying:

The following error occurred converting from datetime to double:

Undefined function 'double' for input arguments of type 'datetime'. To convert from datetimes to numeric, first subtract off a

datetime origin, then convert to numeric using the SECONDS, MINUTES, HOURS, DAYS, or YEARS functions.

Error in test2 (line 38)

P_D(i,1)=data.Dates(i);

How do I convert to numeric? '09-Jul-2019 02:25:00'

[Walter Roberson]

What would you want the numeric value to be?

[James Upton]

anything which I can display on a chart as the date on the X axis and price on the Y axis. That is what I am trying to achieve.

Answer 1

[Walter Roberson]

datenum() the datetime object.

This is not preferred. Consider using a table object or better yet a timetable

[James Upton]

I want to display on a chart the date on the X axis and price on the Y axis. That is what I am trying to achieve.

[Steven Lord]

I second Walter's suggestion of storing your data in a timetable. Once you've done that, you could call plot on the times stored in the timetable as the first input and the numeric data as the second input.

t = datetime('today')+days(0:5).';
r = (0:5).'.^2;

tt = timetable(t, r);
plot(tt.t, tt.r)

Yes, I know in this example I could just as easily have plotted the data using t and r directly. But I'm assuming you may be performing some manipulation or analysis on the data before visualizing it, and many functions can accept a timetable.