# isregular

Determine if timetable is regular with respect to time or calendar unit

## Syntax

``tf = isregular(TT,timeComponent)``
``tf = isregular(TT)``
``````[tf,dt] = isregular(___)``````

## Description

example

````tf = isregular(TT,timeComponent)` returns `1` (`true`) if timetable `TT` is regular with respect to the specified time or calendar unit. Otherwise, it returns `0` (`false`). A timetable is regular if its row times increase or decrease monotonically by the same time step.If the row times of `TT` are `datetime` values, then the time steps between them might be regular with respect to a calendar unit such as months, but irregular with respect to exact elapsed time. Specify the time or calendar unit by using the `timeComponent` input argument.For example, if the row times are regular monthly `datetime` values, and `timeComponent` is `'month'`, then `isregular` returns `1`. But if `timeComponent` is `'time'`, then `isregular` returns `0` because different months can represent different lengths of time.If the row times are `duration` values, then specify `timeComponent` as `'time'` or use the next syntax. The `duration` data type does not represent times using calendar units.```

example

````tf = isregular(TT)` is equivalent to `isregular(TT,'time')`.```

example

``````[tf,dt] = isregular(___)``` returns `dt`, the time step between row times. If `TT` is regular, then `dt` is either a `duration` value or a `calendarDuration` value. If `TT` is not regular, then `dt` is a `NaN` value.```

## Examples

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Create a timetable by using a monthly time vector. Determine whether it is regular with respect to time, and then with respect to months.

Create a timetable whose row times are the first five months of the year `2016`. Add the monthly price of a stock as a table variable.

```StockPrice = [109.0;107.82;113.17;128.01;116]; M = timetable(datetime(2016,1:5,3)',StockPrice)```
```M=5×1 timetable Time StockPrice ___________ __________ 03-Jan-2016 109 03-Feb-2016 107.82 03-Mar-2016 113.17 03-Apr-2016 128.01 03-May-2016 116 ```

Determine whether `M` is a regular timetable.

`TF = isregular(M)`
```TF = logical 0 ```

`M` is not regular because the first five months have different numbers of days. You can use the `diff` function to calculate the differences in the time steps between consecutive times in `M`. The differences are durations, formatted to display the time steps as hours, minutes, and seconds.

`D = diff(M.Time)`
```D = 4x1 duration 744:00:00 696:00:00 744:00:00 720:00:00 ```

Determine whether `M` is regular with respect to months by specifying `'month'` as the unit of measure.

`TF = isregular(M,'months')`
```TF = logical 1 ```

Create a timetable. Determine if it is regular, and then return the size of the time step if it is.

```Time = [minutes(0):minutes(15):minutes(60)]'; Pulse = [72 75 80 73 69]'; TT = timetable(Time,Pulse)```
```TT=5×1 timetable Time Pulse ______ _____ 0 min 72 15 min 75 30 min 80 45 min 73 60 min 69 ```
`[TF,dt] = isregular(TT)`
```TF = logical 1 ```
```dt = duration 15 min ```

`TT` is a regular timetable.

## Input Arguments

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Input timetable.

Time or calendar unit, specified as a character vector or string scalar. `isregular` determines if the row times of `TT` are regular to the time or calendar unit specified by `timeComponent`. The table lists the units that you can specify.

Time or Calendar Unit

Description

`'years'`

Regular to the year

`'quarters'`

Regular to the quarter

`'months'`

Regular to the month

`'weeks'`

Regular to the week

`'days'`

Regular to the day

`'time'` (default)

Regular with respect to time

## Output Arguments

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True or false, returned as a logical `1` if the row times are regular and a logical `0` if they are not.

Time step between row times, returned as a `duration` or `calendarDuration` value. If the timetable is not regular, then `dt` is a `NaN` value.

## Tips

• In certain cases, you can create a timetable while specifying a regular time step between row times, and yet the resulting timetable is irregular. This result occurs when you specify the time step by using a calendar unit of time and there is a row time that introduces an irregular step. For example, if you create a timetable with a time step of one calendar month, starting on January 31, 2019, then it is irregular with respect to months.

```stime = datetime(2019,1,31); tstep = calmonths(1); TT = timetable('Size',[3 1],'VariableTypes',{'double'},... 'TimeStep',tstep,'StartTime',stime); tf = isregular(TT,'month') ```
```tf = logical 0 ```

There are other cases where irregularities are due to shifts from Daylight Saving Time (DST) or to row times that are leap seconds. This table specifies the row time values and time steps that can produce irregular timetables unexpectedly.

Row Time Value

Time Step

Start time specified as the 29th, 30th, or 31st day of the month.

Number of calendar months or quarters.

Start time specified as February 29.

Number of calendar years.

Any row time occurring between 1:00 a.m. and 2:00 a.m. on a day shifting from DST to standard time (when row times are specified as `datetime` values whose time zone observes DST).Number of calendar days or months.

Any row time that is a leap second (when row times are specified as `datetime` values whose time zone is the `UTCLeapSeconds` time zone). For the list of leap seconds, see `leapseconds`.

Time step specified in any calendar unit (days, weeks, months, quarters, or years).

## Extended Capabilities

Introduced in R2016b