Why can't I convert from datenum to datetime?

I am trying to convert a vector of datenums to datetime but for some reason having issues. The spreadsheet I am working with is 7gb so I will just include the top rows.

%Data (d) example:
7.3782e+05    79.064    80.016    75.023    
7.3782e+05    79.137    80.478    75.399
7.3782e+05    78.144    79.663      75.5

d_times=d(:,1);
d_times=datetime(d_times, 'ConvertFrom', 'datenum'); %convert t column datenums to date and time

When I do this I get the error:

Error using datetime (line 658)
Input data must be a numeric array, a string array, a cell array containing character vectors, or a char matrix.

...but I can see that the first value is a datetime? Where am I going wrong?

Answer 1

[Stephen23]

You imported that data into a table (e.g. using readtable) and so you are using the wrong indexing:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

You would need to use curly braces to get the numeric data out of the table:

d_times = d{:,1};
%          ^   ^ you need these

Even better would be to use the variable name (which you have not told us):

d_times = d.nameofthefirstcolumn;

[Louise Wilson]

Thanks Stephen. I didn't include variable names in my table-the first row of the first column was 0. I managed to get around this problem by importing the data using csvread instead. Following this, everything works fine. Since I only needed to do this to check the datetimes were correct following subsetting the data, I will leave it I think. But, this is really good to know! I didn't realise the indexing was wrong. Thank you.

Answer 2

[per isakson]

The datetime statement is ok.

>> d_times=datetime( now, 'ConvertFrom', 'datenum');
>> d_times
d_times = 
  datetime
   27-Apr-2020 05:27:05
>> 

This script

%%
d = [
        7.3782e+05    79.064    80.016    75.023    
        7.3782e+05    79.137    80.478    75.399
        7.3782e+05    78.144    79.663      75.5
    ];
d1 = d(:,1);
%%
d_times = datetime( d1, 'ConvertFrom', 'datenum')

returns

d_times = 
  3×1 datetime array
   30-Jan-2020 00:00:00
   30-Jan-2020 00:00:00
   30-Jan-2020 00:00:00
>> 

I guess there is some kind of problem with your value of d(:,1)

Proposal: Replace

d_times=d(:,1);

by

d1 = d(:,1);

run the script and inspect the value of d1

Try

d1 = d( 1:end-2, 1 );