withtol

Time tolerance for timetable row subscripting

Syntax

S = withtol(rowTimes,tol)

S = withtol(EF,tol)

Description

S = withtol(rowTimes,tol) creates a subscript to select rows of a timetable. S selects all rows whose row times match a time in rowTimes within the tolerance specified by tol. The rowTimes argument is a datetime or duration array, or a cell array of character vectors that specify dates and times. tol must be a nonnegative duration value.

If rowTimes contains datetime values, then you can only use S to subscript into a timetable whose row times are datetime values. Similarly, if rowTimes contains duration values, then you can only use S to subscript into a timetable whose row times are duration values.

S = withtol(EF,tol) creates a row subscript using an event filter. To use event filters, the timetable you subscript into must have an attached event table. For more information on specifying a time tolerance using event filters, see eventfilter. (since R2023a)

Examples

Specify Tolerance to Match Row Times

Create a timetable that contains temperature and pressure data with row times in hours. There is a slight random variance in the row times. Select rows with row times that match corresponding times in a time vector within a tolerance of five seconds.

Time = datetime(2015,12,18) + hours(1:10)' + seconds(randn(10,1));
Temp = [37.3 39.1 42.3 42.6 43 43.9 44.1 43.3 42.5 42]';
Pressure = [29.4 29.6 30.0 30.0 30.1 29.9 29.9 29.8 29.6 29.7]';
TT = timetable(Time,Temp,Pressure)

TT=10×2 timetable
            Time            Temp    Pressure
    ____________________    ____    ________

    18-Dec-2015 01:00:00    37.3      29.4  
    18-Dec-2015 02:00:01    39.1      29.6  
    18-Dec-2015 02:59:57    42.3        30  
    18-Dec-2015 04:00:00    42.6        30  
    18-Dec-2015 05:00:00      43      30.1  
    18-Dec-2015 05:59:58    43.9      29.9  
    18-Dec-2015 06:59:59    44.1      29.9  
    18-Dec-2015 08:00:00    43.3      29.8  
    18-Dec-2015 09:00:03    42.5      29.6  
    18-Dec-2015 10:00:02      42      29.7  

Create a time vector spanning the hours from 3:00 to 8:00.

newTimes = datetime(2015,12,18) + hours(3:8)

newTimes = 1x6 datetime
   18-Dec-2015 03:00:00   18-Dec-2015 04:00:00   18-Dec-2015 05:00:00   18-Dec-2015 06:00:00   18-Dec-2015 07:00:00   18-Dec-2015 08:00:00

Select rows of TT with row times that match times in newTimes within five seconds.

S = withtol(newTimes,seconds(5));
TT2 = TT(S,:)

TT2=6×2 timetable
            Time            Temp    Pressure
    ____________________    ____    ________

    18-Dec-2015 02:59:57    42.3        30  
    18-Dec-2015 04:00:00    42.6        30  
    18-Dec-2015 05:00:00      43      30.1  
    18-Dec-2015 05:59:58    43.9      29.9  
    18-Dec-2015 06:59:59    44.1      29.9  
    18-Dec-2015 08:00:00    43.3      29.8  

Input Arguments

rowTimes — Times to match in timetable

datetime array | duration array | cell array of character vectors | string array

Times to match in a timetable, specified as a datetime array, duration array, cell array of character vectors, or string array. rowTimes contains times that do not exactly match times in the row times of a timetable, but that might be within a specified tolerance.

If rowTimes is a cell array of character vectors or string array, then the elements of the array specify dates and times that the datetime or duration functions can convert.

tol — Tolerance for matching times to row times of timetable

duration | character vector | string scalar

Tolerance for matching times to the row times of a timetable, specified as a duration, character vector, or string scalar. The tolerance value cannot be less than zero.

If tol is a character vector or string scalar, then tol specifies a time that the duration function can convert.

EF — event filter

event filter

Since R2023a

Event filter.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• Event filters are not supported.

For more information, see Code Generation for Timetables (MATLAB Coder) and Timetable Limitations for Code Generation (MATLAB Coder).

Thread-Based Environment
Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

Version History

Introduced in R2016b

R2023a: Specify time tolerance that uses an event filter

When you call withtol, you can specify a time tolerance that find rows around the events found by an event filter. To use event filters, you must first attach an event table to the input timetable. For more information on event tables and event filters, see eventtable and eventfilter.

R2023a: Improved performance when subscripting into timetable with withtol subscript

timetable subscripting when subscripting with a withtol subscript is significantly faster in R2023a than in R2022b.

• When you use a withtol subscript with a timetable that has 10⁷ rows, performance in R2023a is about 44x faster than in R2022b.

  function timingTest()
  rng default
  
  % 10^7 rows
  N = 10000000;
  rowtimes = seconds(0:N-1);
  tt = timetable(rand(N,1),RowTimes=rowtimes);
  
  % 100 values chosen in steps of 10
  n = 1000;
  t = seconds(0:10:n-1);
  
  tt.Time = tt.Time + .1*seconds(rand(N,1));
  wt = withtol(t,seconds(.1));
      
  tic
  tt2 = tt(wt,:);
  toc
  end
  

  The approximate execution times are:

  R2022b: 3.92 s

  R2023a: 0.09 s

The code was timed on a Windows^® 10, AMD^® EPYC 74F3 24-Core Processor @ 3.19 GHz test system by calling each version of the timingTest function.