Matching data and time with sample number

Hi all, i have a data for 24hrs with sampling frequency of fs= 500Hz (so t=1/fs:1/fs:1/fs*length(data)). Now i want to extract the data from a particular time. For example the start time of the data is "11/19/2015 18:00" and i want to find the point in "t" at "11/20/2015 6:34".Can someone please help me with this? I am new to Matlab and not sure how to use datevectors.

[Adam]

What format is your time data in exactly? If you used datavec then I assume it is just in an nx6 double array, but you refer to strings for your times which makes me think your data is in date string format instead.

[Sowmya MR]

I do not have a "time vector". I just have a ECG data with fs=500hz for 24hrs and the starting time of the recording is "11/19/2015 18:00". Now i need to extract the ECG data from time "11/20/2015 6:34".

Answer 1

[dpb]

Find the elapsed time and convert to number of samples--

>> t0='11/19/2015 18:00';target='11/20/2015 6:34';  % given example times
>> dt=datenum(target,'mm/dd/yyyy HH:MM')-datenum(t0,'mm/dd/yyyy HH:MM')  % the time delta
dt =
  0.5236
>> nSampTarget=fix(dt*24*3600*500)
nSampTarget =
  22619999
>>

So, at approximately the 22,620,000th sample will be the beginning of the time history of interest. The originating timestamp will only allow you to locate a precise time down to somewhere around +/- 1 minute which, at 500 Hz, is a number of samples of +/-500*60 = +/30,000