ttB = retime (ttA, newTimes) returns a timetable whose rows sit at newTimes, a datetime or duration vector of the same kind as the row times of ttA, sorted and without repeats.

ttB = retime (ttA, newTimeStep) builds those times instead from a time unit, one of 'secondly', 'minutely', 'hourly', 'daily', 'weekly', 'monthly', 'quarterly' and 'yearly'. The grid starts at the unit’s own boundary at or before the first row time. A filling method reads the times as sample points and runs the grid to the first boundary at or after the last row time, so three hours of data retimed 'daily' spans two days; an aggregating method reads them as bins and stops at the bin holding the last row time, so the same three hours give one day. Weeks begin on Sunday. A duration row time carries no calendar, so a unit measures it only where a duration counts in that unit: 'secondly', 'minutely', 'hourly', 'daily' and 'yearly' are taken and 'weekly', 'monthly' and 'quarterly' are refused.

ttB = retime (ttA, 'regular', …) builds a grid from the first row time in steps of the 'TimeStep' or 'SampleRate' given after it, exactly one of which is required. 'SampleRate' is in hertz. It is bounded by the same rule.

method says how a row that the old times do not carry takes its value. 'fillwithmissing' leaves it missing; 'previous', 'next' and 'nearest' copy a neighbouring value; and 'linear', 'spline', 'pchip' and 'makima' interpolate, which restricts the timetable to numeric, datetime and duration variables. 'default', which is also what no method at all means, reads VariableContinuity and treats a 'continuous' variable as 'linear', a 'step' one as 'previous', and an 'unset' or 'event' one as 'fillwithmissing'.

method may instead aggregate the rows the target times gather into each bin, as 'sum', 'prod', 'mean', 'median', 'mode', 'min', 'max', 'count', 'firstvalue' or 'lastvalue', or as a function handle taking the rows of one bin and returning a single row. A bin holding no row answers 0 for 'sum', 1 for 'prod', 0 for 'count' and missing for the rest, and a function handle is called on it too, with an empty slice of the variable’s own type. Every method but 'count', 'firstvalue' and 'lastvalue' needs a numeric, logical, datetime or duration variable.

'IncludedEdge' says which edge of a bin belongs to it, 'left' by default, under which the last bin runs on past the last target time; 'right' instead lets the first bin run back before the first. A grid built from a unit or a step moves with it: closed on the right it starts at the first bin that can hold a row and ends one unit past the last row time. It is read only by an aggregating method.

An option the chosen method cannot use is warned about and ignored rather than dropped in silence, once per call. MATLAB says nothing in that case.

An aggregation reads the row times as bins rather than as sample points, so it accepts row times that repeat and row times out of order, both of which the other methods refuse.

'fillwithconstant' gives every added row the value of 'Constant', which is required with it and must be a value of the variable’s own kind: a number for a numeric or logical variable, a duration for a duration one, and text for a string or a categorical one, where a name the variable does not yet carry is added to its categories. A number standing for a duration or for text is refused rather than read as days or as digits. Needing no missing value of its own, it serves a variable that has none.

'EndValues' says what a target time outside the span of the old ones takes, either 'extrap' or a constant. It is 'extrap' by default, under which 'linear' and the interpolating methods extrapolate and the neighbouring methods carry the nearest known value outward.

A value that was missing before the call is a gap like any other and is filled with them: a row the new times keep is resampled along with the rest, so 'previous' gives it the last value that was not missing rather than the missing value it held. Only 'fillwithmissing' leaves such a value alone.

Every property of the timetable survives, VariableUnits, VariableDescriptions and VariableContinuity included, and the result carries the time step its new row times imply.

See also: timetable, isregular, fillmissing, synchronize

Source Code: timetable