how to convert date to number

Hi, I have date as below: 2017/11/28 21:16:42, I want to convert it to number using datenum, but in matlab6p5 it give error that 2017 is too large as month. How can I do this? please help some one.

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/releases/R13sp2/techdoc/ref/datenum.html

In MATLAB 6.5, that date format was not supported by datenum(), and that version of datenum() was too early to allow you to pass in a custom date specification.

I suggest that you use sscanf() to break apart the string into numeric pieces, and you can then pass those pieces in to datenum(). Your entries happen to be in the right order so you do not need to re-arrange the numeric parts:

S = '2017/11/28 21:16:42';
datenum( sscanf(S, '%d/%d/%d %d:%d:%d') )

[Mekala balaji]

Sir, If I have date array:For exapmple(my array is even large, >2000 dates), can it work?

S = {'2017/11/28 21:16:42';'2017/11/29 20:06:42';'2018/01/08 1:19:43'}

[Walter Roberson]

 cellfun(@(s) datenum(sscanf(s, '%d/%d/%d %d:%d:%d').'), S)

[Mekala balaji]

Sir, 
It produces the answer as below:

2017
11
28
21
16
42
But I want a single number like:
737027.886597222

[Walter Roberson]

datenum( sscanf(S, '%d/%d/%d %d:%d:%d').' )

[Mekala balaji]

Sir, It works, how to use it for cell array: I used below line, but it gives error.

cellfun(@(s) datenum(sscanf(s, '%d/%d/%d %d:%d:%d').'), S), and it give error
my array is:

S = {'2017/11/28 21:16:42';'2017/12/28 21:16:42';'2017/11/29 20:163:02'}

[Walter Roberson]

What is the error message? I do not have a MATLAB version that old installed at the moment.

[Mekala balaji]

Error:"identifier" expected "(" found.

[Walter Roberson]

It appears that anonymous functions were after your release. You will need to use a for loop.

for K =  1 : length(S)
  result(K) = datenum(sscanf(S{K}, '%d/%d/%d %d:%d:%d').');
end

[Mekala balaji]

Sir, it works,

Sir one more help needed.

I want to calculate time elapsed(cell array):

T1  2017/9/2 21:16:42
T2  2017/9/17 11:34:2
T3  2017/10/23 16:15:23
T4  2017/11/28 22:23:17
T5  2018/1/6 2:21:56
T6  2018/1/13 14:37:33

Current time: 2018/1/13 20:24:22

I want to calculate time difference in hours between "Current time" to T1, T2, T3, T4, T5, T6

[Walter Roberson]

There are two ways you could proceed:

1) https://www.mathworks.com/help/releases/R13sp2/techdoc/ref/etime.html etime() calculates time differences in seconds, which you could then convert to hours; or

2) subtract the two datenum() results to get time differences in days, which you could then convert to hours.

[Mekala balaji]

It works, thanks, Sir.