TF = isregular (D) returns true when the elements of the duration vector D are evenly spaced, that is, when every step from one element to the next is the same and is not zero. A second output DT gives that step, and is NaN when there is none.

A sequence that does not move is not regularly spaced: a step of zero describes no spacing, so isregular of a constant vector is false. A descending vector is regular, with a negative step. A NaN or an infinite element anywhere makes the vector irregular, as does having fewer than two elements, so a scalar and an empty array are both false. D must be a vector; a matrix is an error.

TF = isregular (D, COMPONENT) asks about a particular component, one of 'Years', 'Quarters', 'Months', 'Weeks', 'Days' or 'Time'. A duration measures elapsed time and knows nothing of a calendar, so only 'Time', the default, can be true; every calendar component is false however the vector is spaced. The argument exists so that a duration can be asked the same question as a datetime.

Steps are compared within a few eps of the largest value present rather than exactly, because subtracting neighbouring durations rounds: even one, two and three hours have steps differing in the last bit, and an exact test would call that irregular. MATLAB tolerates a difference of about the same size, for the same reason.

Deviation from MATLAB. A negative step is returned there formatted in seconds whatever the vector’s own format; here the step keeps D’s format whichever way the vector runs.

Source Code: duration