How to convert a datenum to a datetime?

Hi, I have table with column of datenum. I need to do a join with another table which has also a column of date but in just a plain format such as '11/1/2017'. But I got this error: Left and right key variables 'Date' and 'Date' are not comparable because one is a non-cell. How to resolve this error? Thanks a lot!

Answer 1

[Star Strider]

Use the 'ConvertFrom' option:

t = datetime(X,'ConvertFrom','datenum')

[JFz]

Thanks. This line works. But the join is still not working, because the table A.Date is array of cells; table B.Date is array of datetime. How to make them to be either both datetime or cell?

[Star Strider]

Something like this will work:

dt = datetime([now+(0:6)], 'ConvertFrom','datenum')';   % ‘datetime’ Array
dtc = mat2cell(dt, ones(size(dt,1),1), 1);              % ‘cell’ Array
dtt = cell2table(dtc);                                  % ‘table’ Array

Change it appropriately to work with your code.

[JFz]

Thank you! let me try it....

[JFz]

It will take sometime to find out since it is inside a large application.

[JFz]

Works. Thanks!

[Star Strider]

My pleasure!

Answer 2

[Peter Perkins]

Star Strider's answer seems like the long way around. JFz, it always helps to provide a short concrete example so people don't have to guess, but it sounds like you have one table with a datenum variable and another with a datestr variable,

>> t1 = table(floor(now) + [1;2;3],[1;2;3],'VariableNames',{'Date' 'X'})
t1 =
  3×2 table
     Date     X
    ______    _
    737020    1
    737021    2
    737022    3
>> t2 = table(datestr(floor(now) + [3;2;1]),[33;22;11],'VariableNames',{'Date' 'Y'})
t2 =
  3×2 table
       Date        Y 
    ___________    __
    [1x11 char]    33
    [1x11 char]    22
    [1x11 char]    11

and you want to join the two tables using dates as the key. Convert the dates to datetimes, and you're done:

>> t1.Date = datetime(t1.Date,'ConvertFrom','datenum')
t1 =
  3×2 table
            Date            X
    ____________________    _
    21-Nov-2017 00:00:00    1
    22-Nov-2017 00:00:00    2
    23-Nov-2017 00:00:00    3
>> t2.Date = datetime(t2.Date)
t2 =
  3×2 table
       Date        Y 
    ___________    __
    23-Nov-2017    33
    22-Nov-2017    22
    21-Nov-2017    11
>> t3 = join(t1,t2)
t3 =
  3×3 table
            Date            X    Y 
    ____________________    _    __
    21-Nov-2017 00:00:00    1    11
    22-Nov-2017 00:00:00    2    22
    23-Nov-2017 00:00:00    3    33

[JFz]

Yes! You are giving an excellent example. Thank you!