Add up millisecond steps to a certain datetime

I try to add milliseconds to a certain datetime. In dtStart.Var1 the times are in milliseconds (25,50,75, ...). I would like to add this to my current time_of_day. With my code, however, in the end I lose the milliseconds when converting back to datetime.

DateVector = datevec(time_of_day);

A = (dtStart.Var1/1000)+DateVector(:,6);

C = cat(2,DateVector,A);

B = C(:,[1,2,3,4,5,7]);

time = datetime(B,'InputFormat','yyyy-MM-dd HH:mm:ss.SSS');

Answer 1

[Chunru]

Use "Format" for output (not "InputFormat" which is for input).

DateVector = [2021 12 15 01 30 05]

DateVector = 1×6

2021 12 15 1 30 5

 A = DateVector;   
 A(6) = (345/1000)+A(:,6)   % ms: 345

A = 1×6

1.0e+03 * 2.0210 0.0120 0.0150 0.0010 0.0300 0.0053

    time = datetime(A, 'Format','yyyy-MM-dd HH:mm:ss.SSS')

time = datetime
   2021-12-15 01:30:05.345

[Karl Drenker]

Perfect thank you for your quick answer !!

Answer 2

[Siddharth Bhutiya]

You don't need to convert the datetime into a datevec. You can convert your millisecond values into a duration using the milliseconds function and directly add it to the datetime.

>> dt = datetime(2021,12,(1:5)',"Format","dd-MMM-uuuu HH:mm:ss.SSS")

dt = 

  5×1 datetime array

   01-Dec-2021 00:00:00.000
   02-Dec-2021 00:00:00.000
   03-Dec-2021 00:00:00.000
   04-Dec-2021 00:00:00.000
   05-Dec-2021 00:00:00.000

>> millisVals = [100;200;300;123;456];
>> dt = dt + milliseconds(millisVals)

dt = 

  5×1 datetime array

   01-Dec-2021 00:00:00.100
   02-Dec-2021 00:00:00.200
   03-Dec-2021 00:00:00.300
   04-Dec-2021 00:00:00.123
   05-Dec-2021 00:00:00.456