# hours(diff​(datetime(​[t1;t2]))) function

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Berk Opla on 12 Jul 2021
Answered: Peter Perkins on 27 Jul 2021
i have a 300 x 2 table, i want to calculate time differences and i want to count how many of them are more than 3 hours. [a, b] is the size of the table. it gives an error in the = c line & it says Unable to use a value of type duration as an index. how do i solve this?
below is the related part of the code. thank you so much
for n = 1:a
t1 = y(n,1)
t2 = y(n,2)
hours(diff(datetime(t1;t2]))) = c
if c > 3
x = x+ 1
end
end
##### 2 CommentsShowHide 1 older comment
Berk Opla on 12 Jul 2021
yes i'm getting "Unable to use a value of type duration as an index." for the line of
hours(diff(datetime(t1;t2]))) = c

Berk Opla on 12 Jul 2021
Edited: Berk Opla on 12 Jul 2021
figured it out
hours(diff(datetime(t1;t2]))) = c is wrong
it should be c = hours(diff(datetime([t1;t2])))
for some reason
##### 2 CommentsShowHide 1 older comment
Berk Opla on 12 Jul 2021
yeah fixed it now. the problem was the place of the c

dpb on 12 Jul 2021
hours(diff(datetime(t1;t2]))) = c
You're using hours that is a builtin function as an array name on the LHS of an assignment statement and you also have an unmatched "]" bracket in the expression.
You also don't need a loop here...use MATLAB vectorized operations instead...
You don't provide what y variable contains; presuming it can be converted to a datetime, then if the answer is to determine how many of the time differences between the two columns are > 3 hours, then
nGt3=sum((datetime(y:,1)-datetime(y:,2))>3);
This presumes as your code that the first date is in the second column not the first -- one would normally think that would be the other way 'round; in which case would want to reverse the column indices in the difference calculation.

Peter Perkins on 27 Jul 2021
In addition to what others have said, you probably don't need the "hours" in
hours(diff(datetime(t1;t2])))
All that does is turn the duration that diff returns into a number. You are probably better off leaving it as duration, and replacing "3" with hours(3). More expressive.