Using Row Labels in Table and Timetable Operations - MATLAB & Simulink (2024)

Sort on Row Labels

For example, you can sort a timetable on its row times, on one or more of its data variables, or on row times and data variables together.

Create a timetable using the timetable function. A timetable has row times along its first dimension, labeling the rows. The row times are a property of the timetable, not a timetable variable.

Date = datetime(2016,7,[10;10;11;11;10;10;11;11]);X = [1;1;1;1;2;2;2;2];Y = {'a';'b';'a';'b';'a';'b';'a';'b'};Z = [1;2;3;4;5;6;7;8];TT = timetable(X,Y,Z,'RowTimes',Date)

TT=8×3 timetable Time X Y Z ___________ _ _____ _ 10-Jul-2016 1 {'a'} 1 10-Jul-2016 1 {'b'} 2 11-Jul-2016 1 {'a'} 3 11-Jul-2016 1 {'b'} 4 10-Jul-2016 2 {'a'} 5 10-Jul-2016 2 {'b'} 6 11-Jul-2016 2 {'a'} 7 11-Jul-2016 2 {'b'} 8

Rename the first dimension. By default, the name of the first dimension of a timetable is Time. You can access the Properties.DimensionNames property to rename a dimension.

TT.Properties.DimensionNames{1} = 'Date';TT.Properties.DimensionNames

ans = 1x2 cell {'Date'} {'Variables'}

As an alternative, you can specify the row times as the first input argument to timetable, without specifying 'RowTimes'. The timetable function names the row times, or the first dimension, after the first input argument, just as it names the timetable variables after the other input arguments.

TT = timetable(Date,X,Y,Z)

TT=8×3 timetable Date X Y Z ___________ _ _____ _ 10-Jul-2016 1 {'a'} 1 10-Jul-2016 1 {'b'} 2 11-Jul-2016 1 {'a'} 3 11-Jul-2016 1 {'b'} 4 10-Jul-2016 2 {'a'} 5 10-Jul-2016 2 {'b'} 6 11-Jul-2016 2 {'a'} 7 11-Jul-2016 2 {'b'} 8

Sort the timetable by row times. To sort on row times, refer to the first dimension of the timetable by name.

sortrows(TT,'Date')

ans=8×3 timetable Date X Y Z ___________ _ _____ _ 10-Jul-2016 1 {'a'} 1 10-Jul-2016 1 {'b'} 2 10-Jul-2016 2 {'a'} 5 10-Jul-2016 2 {'b'} 6 11-Jul-2016 1 {'a'} 3 11-Jul-2016 1 {'b'} 4 11-Jul-2016 2 {'a'} 7 11-Jul-2016 2 {'b'} 8

Sort by the data variables X and Y. sortrows sorts on X first, then on Y.

sortrows(TT,{'X' 'Y'})

ans=8×3 timetable Date X Y Z ___________ _ _____ _ 10-Jul-2016 1 {'a'} 1 11-Jul-2016 1 {'a'} 3 10-Jul-2016 1 {'b'} 2 11-Jul-2016 1 {'b'} 4 10-Jul-2016 2 {'a'} 5 11-Jul-2016 2 {'a'} 7 10-Jul-2016 2 {'b'} 6 11-Jul-2016 2 {'b'} 8

Sort by row times and X together.

sortrows(TT,{'Date' 'X'})

ans=8×3 timetable Date X Y Z ___________ _ _____ _ 10-Jul-2016 1 {'a'} 1 10-Jul-2016 1 {'b'} 2 10-Jul-2016 2 {'a'} 5 10-Jul-2016 2 {'b'} 6 11-Jul-2016 1 {'a'} 3 11-Jul-2016 1 {'b'} 4 11-Jul-2016 2 {'a'} 7 11-Jul-2016 2 {'b'} 8

Use Row Labels as Grouping or Key Variables

When you group rows together using the rowfun, varfun, stack, and unstack functions, you can specify row labels as grouping variables. When you join tables or timetable together using the join, innerjoin, and outerjoin functions, you can specify row labels as key variables.

For example, you can perform an inner join two tables together, using row names and a table variable together as key variables. An inner join keeps only those table rows that match with respect to the key variables.

Create two tables of patient data. A table can have row names along its first dimension, labeling the rows, but is not required to have them. Specify the last names of patients as the row names of the tables. Add the first names of the patients as table variables.

A = table({'Michael';'Louis';'Alice';'Rosemary';'Julie'},[38;43;45;40;49],... 'VariableNames',{'FirstName' 'Age'},... 'RowNames',{'Garcia' 'Johnson' 'Wu' 'Jones' 'Picard'})

A=5×2 table FirstName Age ____________ ___ Garcia {'Michael' } 38 Johnson {'Louis' } 43 Wu {'Alice' } 45 Jones {'Rosemary'} 40 Picard {'Julie' } 49 

B = table({'Michael';'Beverly';'Alice'},... [64;69;67],... [119;163;133],... [122 80; 109 77; 117 75],... 'VariableNames',{'FirstName' 'Height' 'Weight' 'BloodPressure'},... 'RowNames',{'Garcia' 'Johnson' 'Wu'})

B=3×4 table FirstName Height Weight BloodPressure ___________ ______ ______ _____________ Garcia {'Michael'} 64 119 122 80 Johnson {'Beverly'} 69 163 109 77 Wu {'Alice' } 67 133 117 75 

If a table has row names, then you can index into it by row name. Indexing by row names is a convenient way to select rows of a table. Index into B by a patient's last name to retrieve information about the patient.

B('Garcia',:)

ans=1×4 table FirstName Height Weight BloodPressure ___________ ______ ______ _____________ Garcia {'Michael'} 64 119 122 80 

Perform an inner join on the two tables. Both tables use the last names of patients as row names, and contain the first names as a table variable. Some patients in the two tables have matching last names but different first names. To ensure that both last and first names match, use the row names and FirstName as key variables. To specify the row names as a key or grouping variable, use the name of the first dimension of the table. By default, the name of the first dimension is 'Row'.

C = innerjoin(A,B,'Keys',{'Row','FirstName'})

C=2×5 table FirstName Age Height Weight BloodPressure ___________ ___ ______ ______ _____________ Garcia {'Michael'} 38 64 119 122 80 Wu {'Alice' } 45 67 133 117 75 

If you rename the first dimension of a table, then you can refer to the row names by that name instead of using 'Row'. Perform the same inner join as above but use a different name to refer to the row names.

Show the dimension names of A by accessing its Properties.DimensionNames property.

A.Properties.DimensionNames

ans = 1x2 cell {'Row'} {'Variables'}

Change the name of the first dimension of the table by using its Properties.DimensionNames property. Then use the new name as a key variable.

A.Properties.DimensionNames{1} = 'LastName';A.Properties.DimensionNames

ans = 1x2 cell {'LastName'} {'Variables'}

Perform an inner join on A and B using LastName and FirstName as key variables.

B.Properties.DimensionNames{1} = 'LastName';D = innerjoin(A,B,'Keys',{'LastName','FirstName'})

D=2×5 table FirstName Age Height Weight BloodPressure ___________ ___ ______ ______ _____________ Garcia {'Michael'} 38 64 119 122 80 Wu {'Alice' } 45 67 133 117 75 

Notes on Use of Table Functions and Row Labels