How to validate that one datetime is greater than another

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Rich006
Rich006 2024-5-17
评论： Rich006 2024-5-20
My class takes two datetimes startTime and endTime as input arguments. I would like to use argument validation to force endTime to be later than startTime, but mustBeGreaterThan does not accept datetimes.

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采纳的回答

Stephen23
Stephen23 2024-5-17
编辑：Stephen23 2024-5-17
Ran in:
Do NOT convert to low-precision serial date numbers! Avoid deprecated DATENUM !
Argument validation lets you define your own validation function, which makes your task easy (and you get to write exactly the informative error messages that you want to see displayed):
A = datetime(1994,1,1);
B = datetime(2024,1,1);
myfun(A,B)
okay!
myfun(B,A)
Error using solution>myfun (line 9)
Invalid argument at position 2. End time must be after start time.
function myfun(startTime,endTime)
arguments
startTime (1,1) {idt}
endTime (1,1) {idt,ilt(startTime,endTime)}
end
disp('okay!')
end
function idt(x)
assert(isdatetime(x),'Input must be a DATETIME.')
end
function ilt(s,e)
assert(s<e,'End time must be after start time.')
end
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Stephen23
Stephen23 2024-5-17
编辑：Stephen23 2024-5-17
Ran in:
Some changes:
  • move the validation functions to local functions (rather than methods),
  • do not use the same name for the method and the class,
  • define the class object as a method input. This requirement is explained here:
https://www.mathworks.com/help/matlab/matlab_oop/class-components.html#bupsck8
https://www.mathworks.com/help/matlab/matlab_oop/specifying-methods-and-functions.html
After that (see attached file), it works as expected:
A = datetime(1994,1,1);
B = datetime(2024,1,1);
obj = myClass();
obj.myMethod(A,B)
okay!
obj.myMethod(B,A)
Error using myClass/myMethod (line 7)
Invalid argument at position 3. End time must be after start time.
Rich006
Rich006 2024-5-20
That still isn't what I was trying to do, because it requires running a method after construction. But I did use your suggestion of standalone validation functions. This allows me to create my own mustBeLater. And that answers my question!
classdef myClass
properties
startTime
endTime
end
methods
function obj = myClass(s,e)
arguments
s datetime
e datetime {mustBeLater(e,s)}
end
obj.startTime = s;
obj.endTime = e;
disp('Success!')
end
end
end
function mustBeLater(laterTime,earlierTime)
if laterTime < earlierTime
error("End time must be after start time.")
end
end
>> A = datetime('yesterday');
>> B = datetime('now');
>> obj = myClass(A,B);
Success!
>> obj = myClass(B,A);
Error using myClass
obj = myClass(B,A);
↑
Invalid argument at position 2. End time must be after start time.
(sorry, not sure how to format the inline command inputs/outputs)

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更多回答（2 个）

Joshua Levin Kurniawan
You can use traditional logical operator for datatime. Operator "<", if true, means that the first datatime will occurs sooner than the next variable. In this case, just use the following code
if startTime < endTime
disp("The data is valid");
else
disp("The data is invalid");
end
For further information, you can check out the following page
https://www.mathworks.com/help/matlab/matlab_prog/compare-dates-and-time.html
Fangjun Jiang
Fangjun Jiang 2024-5-17
编辑：Fangjun Jiang 2024-5-17
Ran in:
It seems fine in R2022b, R2023b and R2024a
a=now;
b=now;
mustBeGreaterThan(b,a)
mustBeGreaterThan(a,b)
Value must be greater than 739389.6563.
  2 个评论
Rich006
Rich006 2024-5-17
It works with numbers, but I'm trying to compare datetime objects.
Fangjun Jiang
Fangjun Jiang 2024-5-17
编辑：Fangjun Jiang 2024-5-17
Ran in:
okay, I thought now() returns a datetime object. It was not. You can convert it to datenum()
a=datetime('now');
b=datetime('now');
mustBeGreaterThan(datenum(b),datenum(a))
mustBeGreaterThan(datenum(a),datenum(b))
Value must be greater than 739389.6782.

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