Handling Non-Uniform Time Steps During Timetable Schema Modifications

Confirmed facts

MATLAB timetable stores the time vector in the RowTimes property, which is completely separate from the data variables. Operations that change the variable schema—such as addvars, removevars, or assigning a new value to a variable (TT.VarName = …)—do not alter RowTimes. Consequently, the mapping from each row index to its timestamp remains unchanged unless you explicitly modify RowTimes.

Likely explanation

The internal indexing used by timetable for row access (TT(i,:)) relies on the RowTimes vector. As long as that vector is not altered, the temporal relationship between rows is preserved even when the underlying time steps are non‑uniform. The timetable subclass does not impose additional constraints on schema changes beyond those of the base table class; the only restriction is that you cannot change row times indirectly through variable‑only functions.

Steps for safe schema modification on a non‑uniform timetable

1. Preserve the original row times: originalTimes = TT.RowTimes;
2. Perform the desired variable changes using table‑compatible functions, e.g., TT = addvars(TT, newVar, 'Before', 'Var1'); or TT.Var2 = cast(TT.Var2, 'double');.
3. After modifications, verify that row times are unchanged: assert(isequal(TT.RowTimes, originalTimes), 'Row times were altered unintentionally');
4. If you need to change the time vector itself, do so explicitly (TT.RowTimes = newTimes;) and then re‑align any dependent calculations.

When to ask for a diagnostic detail

If you suspect that RowTimes was altered (e.g., you used a function that returns a timetable with modified times), ask: Did any step assign directly to TT.RowTimes or use a function like retime or synchronize that could have changed the time vector? Knowing this determines whether you need to restore the original times or accept the new timing.