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Select Timetable Data by Row Time and Variable Type
A timetable is a type of table that associates a time with each row. You can subscript into a timetable to select subsets of its data in a number of different ways. To select timetable rows with row times that fall within a given time range, specify the time range using the timerange function. Since a timetable is a table, you can index on rows and variables using either smooth parentheses or curly braces. You can index on specific row times, or select rows with row times that match specified times within a tolerance you set using the withtol function. You can also subscript into a table or timetable to select all the variables that match a type you specify with the vartype function. Finally, extract data from a timetable into a matrix using the Variables property.
Create Timetable from File
Create a timetable from the sample file outages.csv, containing data representing electric utility outages in the United States. Read the table from the file with the readtable function. Convert T.Cause and T.Region into categorical arrays. Then convert the table to a timetable using the table2timetable function. Display the first five rows of the timetable. TT is a timetable containing outage data from February 2002 to January 2014.
T = readtable('outages.csv');
T.Cause = categorical(T.Cause);
T.Region = categorical(T.Region);
TT = table2timetable(T);
TT(1:5,:)
ans =
OutageTime Region Loss Customers RestorationTime Cause
________________ _________ ______ __________ ________________ _______________
02/01/2002 12:18 SouthWest 458.98 1.8202e+06 02/07/2002 16:50 winter storm
01/23/2003 00:49 SouthEast 530.14 2.1204e+05 NaT winter storm
02/07/2003 21:15 SouthEast 289.4 1.4294e+05 02/17/2003 08:14 winter storm
04/06/2004 05:44 West 434.81 3.4037e+05 04/06/2004 06:10 equipment fault
03/16/2002 06:18 MidWest 186.44 2.1275e+05 03/18/2002 23:23 severe storm
Summarize Timetable and Access Row Times
Display a summary of TT. It is a timetable that contains 1468 rows and five variables.
summary(TT)
RowTimes:
OutageTime: 1468×1 datetime
Values:
min 02/01/2002 12:18
median 03/18/2010 21:05
max 01/15/2014 02:41
Variables:
Region: 1468×1 categorical
Values:
MidWest 142
NorthEast 557
SouthEast 389
SouthWest 26
West 354
Loss: 1468×1 double
Values:
min 0
median 180.26
max 23418
NaNs 604
Customers: 1468×1 double
Values:
min 0
median 75765
max 5.9689e+06
NaNs 328
RestorationTime: 1468×1 datetime
Values:
min 07-Feb-2002
median 31-Mar-2010
max 18-Sep-2042
NaTs 29
Cause: 1468×1 categorical
Values:
attack 294
earthquake 2
energy emergency 188
equipment fault 156
fire 25
severe storm 338
thunder storm 201
unknown 24
wind 95
winter storm 145
Access the row times. The row times are not in a variable. Instead, the vector of row times is a property of the timetable. However, you can access the row times with dot syntax. TT.OutageTime is a 1468-by-1 vector of datetime values. Display the first five rows of TT.OutageTime.
TT.OutageTime(1:5)
ans = 5×1 datetime array 02/01/2002 12:18 01/23/2003 00:49 02/07/2003 21:15 04/06/2004 05:44 03/16/2002 06:18
Subscript on Time Range
To select all timetable rows that fall in a time range, create a subscript as a helper, using the timerange function. The start and end times you specify do not have to match any of the row times in the timetable.
Select all rows with outages that occurred between January 2002 and December 2003. Display the first five rows of TT2.
TR = timerange('2002-01-01','2003-12-31'); TT2 = TT(TR,:); TT2(1:5,:)
ans =
OutageTime Region Loss Customers RestorationTime Cause
________________ _________ ______ __________ ________________ ____________
02/01/2002 12:18 SouthWest 458.98 1.8202e+06 02/07/2002 16:50 winter storm
01/23/2003 00:49 SouthEast 530.14 2.1204e+05 NaT winter storm
02/07/2003 21:15 SouthEast 289.4 1.4294e+05 02/17/2003 08:14 winter storm
03/16/2002 06:18 MidWest 186.44 2.1275e+05 03/18/2002 23:23 severe storm
06/18/2003 02:49 West 0 0 06/18/2003 10:54 attack
Display the last five rows of TT2.
TT2(end-4:end,:)
ans =
OutageTime Region Loss Customers RestorationTime Cause
________________ _________ ______ __________ ________________ ________________
09/02/2003 19:46 SouthEast 0 0 09/16/2003 22:25 severe storm
09/15/2003 14:56 MidWest 418.7 61045 09/22/2003 04:21 thunder storm
09/24/2003 22:43 SouthWest 2576.9 9.4873e+05 09/25/2003 14:46 severe storm
09/18/2003 10:40 SouthWest 301.8 2.3973e+05 09/27/2003 08:17 severe storm
10/11/2003 19:36 SouthEast 309.8 93582 10/11/2003 19:49 energy emergency
TT2 is a timetable with only 98 rows, containing outage data only from 2002 and 2003.
Index on Specified Times
You can index into TT with datetime values or character vectors representing specific times in TT.OutageTime. But when you do so, the times you specify must have exact matches in the time vector, and only those times are selected. Index into TT on times for the first and third rows of TT.
TT({'2002-02-01 12:18:00','2003-02-07 21:15:00'},:)
ans =
OutageTime Region Loss Customers RestorationTime Cause
________________ _________ ______ __________ ________________ ____________
02/01/2002 12:18 SouthWest 458.98 1.8202e+06 02/07/2002 16:50 winter storm
02/07/2003 21:15 SouthEast 289.4 1.4294e+05 02/17/2003 08:14 winter storm
Index on Specified Times with Tolerances
Specify a tolerance when indexing on times. You can use the withtol function to create a subscript as a helper. With the output of withtol, you can select row times that match within the specified tolerance.
Index into TT on specified dates. Specify a tolerance of one day to return rows with row times that are within one day of the specified dates. The times must be in a datetime or duration vector, or in a cell array of character vectors that can be converted to datetime or duration values. The tolerance must be specified as a duration, using a function such as seconds, minutes, hours, or days.
rowTimes = {'2002-02-01','2003-02-07'};
S = withtol(rowTimes,days(1));
TT(S,:)
ans =
OutageTime Region Loss Customers RestorationTime Cause
________________ _________ ______ __________ ________________ ____________
02/01/2002 12:18 SouthWest 458.98 1.8202e+06 02/07/2002 16:50 winter storm
02/07/2003 21:15 SouthEast 289.4 1.4294e+05 02/17/2003 08:14 winter storm
Subscript by Variable Type
To select all timetable variables that are of a given type, create a subscript as a helper, using the vartype function. You can specify variable types without having to specify their names or positions in the timetable.
Select all variables that contain numeric data. TT2 contains only the variables Loss and Customers. The other three variables of TT are either categorical or datetime variables. Display the first five rows of TT2.
S = vartype('numeric');
TT2 = TT(:,S);
TT2(1:5,:)
ans =
OutageTime Loss Customers
________________ ______ __________
02/01/2002 12:18 458.98 1.8202e+06
01/23/2003 00:49 530.14 2.1204e+05
02/07/2003 21:15 289.4 1.4294e+05
04/06/2004 05:44 434.81 3.4037e+05
03/16/2002 06:18 186.44 2.1275e+05
Subscript both on a time range and by variable type.
TR = timerange('2002-01-01','2003-12-31'); TT2 = TT(TR,S); TT2(1:5,:)
ans =
OutageTime Loss Customers
________________ ______ __________
02/01/2002 12:18 458.98 1.8202e+06
01/23/2003 00:49 530.14 2.1204e+05
02/07/2003 21:15 289.4 1.4294e+05
03/16/2002 06:18 186.44 2.1275e+05
06/18/2003 02:49 0 0
Extract Data with Variables Property
Tables and timetables have a property, Variables, that you can use to extract data from variables into a matrix, as long as the variables can be concatenated together.
Extract the numeric data from TT2 using the Variables property. A is a 1468-by-2 matrix of doubles. When you extract data from a timetable into an array, the row times are not included.
A = TT2.Variables; A(1:5,:)
ans =
1.0e+06 *
0.0005 1.8202
0.0005 0.2120
0.0003 0.1429
0.0002 0.2128
0 0
The result of TT2.Variables is the same as the result of using curly braces to extract data, using the TT2{:,:} syntax.
You can concatenate the variables in TT2 into an array of doubles. However, TT contains numeric, categorical, and datetime variables that cannot be concatenated. The Variables property returns an error when variables cannot be concatenated. To avoid such an error, you can subscript by variable type before using the Variables property.
Subscript into TT to select numeric variables and extract them into a matrix.
A = TT(:,vartype('numeric')).Variables;
A(1:5,:)
ans =
1.0e+06 *
0.0005 1.8202
0.0005 0.2120
0.0003 0.1429
0.0004 0.3404
0.0002 0.2128
See Also
retime | synchronize | table2timetable | timerange | timetable | vartype | withtol
