Why is day() function throwing me this error: Check for missing argument or incorrect argument data type in call to function 'day'?

Having this task:

Perform a regression model over the normalized active cases in China using the model.....(long assignment that I'm not worried about). Tip: To convert from datetime to a numeric variable for the regression, use x=day(date-min(date(:)))+1; being “date” the datetime vector return from getdata function.

This is what I have until now:

function RP_ejercicio1
    
    data = readtable('COVID-19.csv');
    [active_res, confirmed_res, death_res, recovered_res, date]  = getdata(data, 'China', 93/147);
    
    x=day(date-min(date(:)))+1;
    y = active_res;
    yp = log(y./x);
    a = [x ones(size(x))];
    sol = inv(a'*a)*(a'*yp);
    b = sol(1);
    c = sol(2);
    a = exp(c);
    
end

I'm getting an error in this line

x=day(date-min(date(:)))+1;

and I don't get it. From getdata function I'm getting successfully a 1x50 datetime array fulled with dates and stored in my date variable. What am I doing wrong?

[Shalini K]

letterds = datastore("*_M_*.txt"); data = read(letterds); data = scale(data); plot(data.X,data.Y) axis equal plot(data.Time,data.Y) ylabel("Vertical position") xlabel("Time")

Answer 1

[Cris LaPierre]

Based on the arithmetic you are doing with your date, I think you want to use the function days instead of day. The former returns the number of elapsed days as a duration, which is typically what you want when you subtract two dates. The later extracts the day number from a date, as in day of the month.

x=days(date-min(date(:)))+1;

[Francisco Javier Pérez Sánchez]

You can't imagine how much I owe you, I was just giving up. You are right, it's a mistake in the task. I can finally keep with my work after hours of frustration.

Again, thank you very much.

[Cris LaPierre]

I only know because I've made the mistake myself. Glad to have helped.