How to get only duration calculated from datetime type variables as an integer/real scalar?

Hi,

I have some data from a sensor with date-time values and I need to compute something like below:

timeduration = max(datetimevalue) - min(datetimevalue);

rate = A/timeduration ;%A is a set of double values; sensor readings within the duration

where, max(datetimevalue) = 02-Dec-2016 15:30:26 and min(datetimevalue) = 02-Dec-2016 15:30:06

So I get timeduration as 00:00:20.

when I use rate = A/timeduration, it shows an error 'The denominator in matrix division for duration arrays must be a real scalar double value'.

What I want to do is, let matlab calculate the duration and take the duration as an integer (in the above case it is 20) and calculate the rate.

How do I do this? For an experiment or two, I can manually change it, but when I have many experiments to do, I would like to make matlab do it automatically so I do not have to hard-code it. (I have tried using etime, but no good).

Thanks in advance.

Answer 1

[Steven Lord]

What do you want that scalar to be? How many years, days, hours, minutes, seconds, or milliseconds that duration represents? There are functions for each of those. In this context you're probably looking for seconds. If S = seconds(X) and "X is a duration array, then S is a double array with each element equal to the number of seconds in the corresponding element of X."

[lexi11]

Thank you very much, this works!

Answer 2

[Geoff Hayes]

laksi11 - one way would be for you to convert your datetime values into serial numbers using datenum as

 timeDurationSerial = datenum(max(datetimevalue)) - datenum(min(datetimevalue));

and then convert that duration into seconds as

 timeDurationSec = timeDurationSerial*86400;

The timeDurationSerial is a serial number which represents the whole and fractional number of days from a fixed, preset date. So we convert this difference to seconds using 86400 (the number of seconds in a day). Your code could then be simply

 timeDurationSerial = (datenum(max(datetimevalue)) - datenum(min(datetimevalue)))*86400;

The above should work...I can't test it out since R2014a doesn't have the datetime function.

[Sean de Wolski]

I would not recommend this. Datetime has many features lacking from datenum, use the conversion functions like seconds, hours, etc. to get the double output.

[lexi11]

Geoff Hayes: thank you very much. Your method works too!

Sean de Wolski: thank you for your useful comment. Both these methods work.

Answer 3

[Mohd Owais]

% Usain Bolt's 100-meter dash record

distance = 100; % meters

time = 9.58; % seconds

hundred = (distance/time) * 3.6; % km/h

% Eliud Kipchoge's marathon record

distance = 42.195; % kilometers

time = hours(2) + minutes(1) + seconds(39); % convert to duration

marathon = (distance/time) * 3.6; % km/h

[Mohd Owais]

The denominator in matrix division for duration arrays must be a real scalar double value.

[Walter Roberson]

distance / hours(time)

[Steven Lord]

Convert your second time variable into a number of hours using the hours function.

time = hours(2) + minutes(1) + seconds(39)

time = duration
   2.0275 hr

timeInHours = hours(time)

timeInHours = 2.0275

whos

  Name             Size            Bytes  Class       Attributes

  cmdout           1x33               66  char                  
  time             1x1                10  duration              
  timeInHours      1x1                 8  double                

Note that time is a duration array while timeInHours is a double value.