I'm trying to convert date numbers to character dates, I created a vector using datenum and manually entering each date in Y,M,D,H,M,S format, and it works but I hope to find

Hi I'm still a newbie, I'm trying to convert date numbers to character dates, I created a vector using datenum and manually entering each date in Y,M,D,H,M,S format, and it works BUT, I have a ton of files and it takes me forever to write and add to the vector each day in Y,M,D,H,M,S format, because I have to manually change each day everytime I run a different set of files.

This is what I have and it works:

dvec = [ datenum(2018,07,28,02,27,32); datenum(2018,07,28,19,18,50); datenum(2018,07,28,21,27,19); datenum(2018,07,28,14,08,06); ...];

I've been going over the documenation I could find and this is what I'm trying but it doesn't work (it just shows the last date in the struct):

DateNumber = daily_names.datenum;
formatOut = 'mm dd';
str = datestr(DateNumber,formatOut);

Ps.

daily_names is a struct with datenum as a column and what I'm ultimately trying to do, is to automatically have the X axis in a plot, show the dates of the data.

Thank you!! All advice is appreciated

[Walter Roberson]

Why are you using datenum() and datestr() instead of datetime() ?

Answer 1

[Steven Lord]

Instead of using serial date numbers with datenum, use datetime.

% Arbitrary data. I entered this manually, but you could build these
% vectors automatically by reading from a file (for example) or using the
% normal vector creation tools like the colon operator (see y)
y = (2020:2022).';
mo = [6; 3; 11];
d = [4; 12; 1];
h = [4; 8; 5];
mi = [15; 16; 23];
s = [42; 20; 01];
T = datetime(y, mo, d, h, mi, s) 

T = 3×1 datetime array
   04-Jun-2020 04:15:42
   12-Mar-2021 08:16:20
   01-Nov-2022 05:23:01

You can directly plot with datetime arrays.

plot(T, 1:3, 'o-')

Answer 2

[Stephen23]

As Steven Lord and Walter Roberson and the MATLAB documentation recommended, you should use DATETIME objects, which can be plotted directly (no need to convert to text).

You can simply convert your structure data like so:

T = datetime([daily_names.datenum], 'ConvertFrom','datenum', 'Format','MM dd')

Avoid using the less accurate, less versatile, deprecated functions DATENUM, DATEVEC, and DATESTR. The recommended DATETIME objects support many many functions and can be plotted directly: read the help to know more about them:

https://www.mathworks.com/help/matlab/date-and-time-operations.html

[Margarita Rivera]

Thank you Steven!! For some reason it shows the date the data was downloaded as opposed to the date the data is from, but I agree it should work. The dates I need are in the datenum column in daily_names, and the date the data was downloaded is in a different column, so I'm not sure why its happening.

But I appreciate your help, I'll keep at it, thank you!