Combine two tables or timetables by rows using key variables (2024)

Combine two tables or timetables by rows using key variables

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Syntax

T = join(Tleft,Tright)

T = join(Tleft,Tright,Name,Value)

[T,iright]= join(___)

Description

example

T = join(Tleft,Tright) combines the tables or timetables Tleft and Tright by merging rows from the two inputs. The join function performs a simple form of the join operation where each row of Tleft must match exactly one row in Tright. Rows match where the corresponding values in the key variables are the same. The output combines all rows from Tleft with the rows from Tright where the key variables have matching values.

For example, if Tleft has variables named Key1 and Var1, and Tright has variables Key1 and Var2, then T=join(Tleft,Tright) uses Key1 as a key variable.

By default, the key variables are:

Variables that have the same names in Tleft and Tright, if both inputs are tables, or if Tleft is a timetable and Tright is a table.
Vectors of row times, if both Tleft and Tright are timetables.

The matching values of the key variables do not have to be in the same orders in the left and right inputs. Also, the key variables of Tright must contain all values in the key variables of Tleft. Each value must occur only once in the key variables of Tright, but can occur multiple times in the key variables of Tleft. Therefore, the join operation replicates any row from Tright that matches multiple rows from Tleft.

The inputs can be tables, timetables, or one of each.

If Tleft is a table, then join returns T as a table.
If Tleft is a timetable, then join returns T as a timetable.

example

T = join(Tleft,Tright,Name,Value) joins the tables or timetables with additional options specified by one or more Name,Value pair arguments.

For example, you can specify which variables to use as key variables.

example

[T,iright]= join(___) also returns an index vector iright such that each element of iright identifies the row in Tright that corresponds to that row in T. You can use this syntax with any of the input arguments of the previous syntaxes.

Examples

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Append Values from One Table to Another

Open Live Script

Create a table, Tleft.

Tleft = table({'Janice','Jonas','Javier','Jerry','Julie'}',[1;2;1;2;1],... 'VariableNames',{'Employee' 'Department'})

Tleft=5×2 table Employee Department __________ __________ {'Janice'} 1 {'Jonas' } 2 {'Javier'} 1 {'Jerry' } 2 {'Julie' } 1

Create a table, Tright, with a variable in common with Tleft.

Tright = table([1 2]',{'Mary' 'Mona'}',... 'VariableNames',{'Department' 'Manager'})

Tright=2×2 table Department Manager __________ ________ 1 {'Mary'} 2 {'Mona'}

Create a new table, T, containing data from tables Tleft and Tright. Use the join function to repeat and append Manager data from table Tright to the data from table Tleft, based on the key variable, Department.

T = join(Tleft,Tright)

T=5×3 table Employee Department Manager __________ __________ ________ {'Janice'} 1 {'Mary'} {'Jonas' } 2 {'Mona'} {'Javier'} 1 {'Mary'} {'Jerry' } 2 {'Mona'} {'Julie' } 1 {'Mary'}

Merge Tables with One Variable in Common

Open Live Script

Create a table, Tleft.

Tleft = table([5;12;23;2;6],... {'cereal';'pizza';'salmon';'cookies';'pizza'},... 'VariableNames',{'Age','FavoriteFood'},... 'RowNames',{'Amy','Bobby','Holly','Harry','Sally'})

Tleft=5×2 table Age FavoriteFood ___ ____________ Amy 5 {'cereal' } Bobby 12 {'pizza' } Holly 23 {'salmon' } Harry 2 {'cookies'} Sally 6 {'pizza' }

Create a table, Tright, with one variable in common with Tleft.

Tright = table({'cereal';'cookies';'pizza';'salmon';'cake'},... [110;160;140;367;243],... {'B';'D';'B-';'A';'C-'},... 'VariableNames',{'FavoriteFood','Calories','NutritionGrade'})

Tright=5×3 table FavoriteFood Calories NutritionGrade ____________ ________ ______________ {'cereal' } 110 {'B' } {'cookies'} 160 {'D' } {'pizza' } 140 {'B-'} {'salmon' } 367 {'A' } {'cake' } 243 {'C-'}

Create a new table, T, with data from tables Tleft and Tright. The variable in common, FavoriteFood, is used as a key variable by the join function.

T = join(Tleft,Tright)

T=5×4 table Age FavoriteFood Calories NutritionGrade ___ ____________ ________ ______________ Amy 5 {'cereal' } 110 {'B' } Bobby 12 {'pizza' } 140 {'B-'} Holly 23 {'salmon' } 367 {'A' } Harry 2 {'cookies'} 160 {'D' } Sally 6 {'pizza' } 140 {'B-'}

Table T does not include information from the last row of table Tright about 'cake' because there is no corresponding entry in table Tleft.

Merge Tables by Specifying One Key Variable

Open Live Script

Create a table, Tleft.

Tleft = table([10;4;2;3;7],[5;4;9;6;1],[10;3;8;8;4])

Keep One Copy of Nonkey Variables

Open Live Script

Create a new table with data from tables Tleft and Tright. If any nonkey variables have the same name in both tables, keep only the copy from table Tleft.

Create a table, Tleft.

Tleft = table([10;4;2;3;7],[5;4;9;6;1])

Tleft=5×2 table Var1 Var2 ____ ____ 10 5 4 4 2 9 3 6 7 1

Create a table, Tright, giving Var2 of table Tright the same contents as Var2 from table Tleft.

Tright = table([6;1;1;6;8],[5;4;9;6;1],[10;3;8;8;4])

Tright=5×3 table Var1 Var2 Var3 ____ ____ ____ 6 5 10 1 4 3 1 9 8 6 6 8 8 1 4

Create a new table, T, with data from tables Tleft and Tright. Use Var2 as a key variable to the join function and keep only the copy of Var1 from table Tleft. The output table T does not contain the Var1 data from table Tright.

T = join(Tleft,Tright,'Keys','Var2','KeepOneCopy','Var1')

T=5×3 table Var1 Var2 Var3 ____ ____ ____ 10 5 10 4 4 3 2 9 8 3 6 8 7 1 4

Merge Tables Using Row Names as Keys

Open Live Script

Create a table, Tleft.

Tleft = table(['M';'M';'F';'F';'F'],[38;43;38;40;49],... 'VariableNames',{'Gender' 'Age'},... 'RowNames',{'Smith' 'Johnson' 'Williams' 'Jones' 'Brown'})

Tleft=5×2 table Gender Age ______ ___ Smith M 38 Johnson M 43 Williams F 38 Jones F 40 Brown F 49

Create a table, Tright, such that the rows of Tleft and the rows of Tright have a one-to-one correspondence.

Tright = table([64;69;67;71;64],... [119;163;133;176;131],... [122 80; 109 77; 117 75; 124 93; 125 83],... 'VariableNames',{'Height' 'Weight' 'BloodPressure'},... 'RowNames',{'Brown' 'Johnson' 'Jones' 'Smith' 'Williams'})

Tright=5×3 table Height Weight BloodPressure ______ ______ _____________ Brown 64 119 122 80 Johnson 69 163 109 77 Jones 67 133 117 75 Smith 71 176 124 93 Williams 64 131 125 83

Create a new table, T, with data from tables Tleft and Tright. Use the vectors of row names as key variables. (The name of the vector of row names of a table is 'Row', as shown by Tleft.Properties.DimensionNames{1}.)

T = join(Tleft,Tright,'Keys','Row')

T=5×5 table Gender Age Height Weight BloodPressure ______ ___ ______ ______ _____________ Smith M 38 71 176 124 93 Johnson M 43 69 163 109 77 Williams F 38 64 131 125 83 Jones F 40 67 133 117 75 Brown F 49 64 119 122 80

The rows of T are in the same order as Tleft.

Merge Tables Using Left and Right Keys

Open Live Script

Create a table, Tleft.

Tleft = table([10;4;2;3;7],[5;4;9;6;1],[10;3;8;8;4])

Tleft=5×3 table Var1 Var2 Var3 ____ ____ ____ 10 5 10 4 4 3 2 9 8 3 6 8 7 1 4

Create a table, Tright, giving Var2 of table Tright the same contents as Var1 from table Tleft, but in a different order.

Tright = table([6;1;1;6;8],[2;3;4;7;10])

Tright=5×2 table Var1 Var2 ____ ____ 6 2 1 3 1 4 6 7 8 10

Create a new table, T, containing data from tables Tleft and Tright. Use Var1 from table Tleft with Var2 from table Tright as key variables to the join function.

[T,iright] = join(Tleft,Tright,'LeftKeys',1,'RightKeys',2)

T=5×4 table Var1_Tleft Var2 Var3 Var1_Tright __________ ____ ____ ___________ 10 5 10 8 4 4 3 1 2 9 8 6 3 6 8 1 7 1 4 6

iright = 5×1 5 3 1 2 4

T is the horizontal concatenation of Tleft and Tright(iright,1).

Merge Timetables

Open Live Script

Create two timetables that have the same row times but different variables.

Traffic = [0.8 0.9 0.1 0.7 0.9]';Noise = [0 1 1.5 2 2.3]';Tleft = timetable(hours(1:5)',Traffic,Noise)

Tleft=5×2 timetable Time Traffic Noise ____ _______ _____ 1 hr 0.8 0 2 hr 0.9 1 3 hr 0.1 1.5 4 hr 0.7 2 5 hr 0.9 2.3

Distance = [0.88 0.86 0.91 0.9 0.86]';Tright = timetable(hours(1:5)',Distance)

Tright=5×1 timetable Time Distance ____ ________ 1 hr 0.88 2 hr 0.86 3 hr 0.91 4 hr 0.9 5 hr 0.86

Merge the timetables. join uses the row times as the key variables.

T = join(Tleft,Tright)

T=5×3 timetable Time Traffic Noise Distance ____ _______ _____ ________ 1 hr 0.8 0 0.88 2 hr 0.9 1 0.86 3 hr 0.1 1.5 0.91 4 hr 0.7 2 0.9 5 hr 0.9 2.3 0.86

Merge Timetable and Table

Open Live Script

Create a timetable and a table.

Measurements = [0.13 0.22 0.31 0.42 0.53 0.57 0.67 0.81 0.90 1.00]';Device = ['A';'B';'A';'B';'A';'B';'A';'B';'A';'B'];Tleft = timetable(seconds(1:10)',Measurements,Device)

Tleft=10×2 timetable Time Measurements Device ______ ____________ ______ 1 sec 0.13 A 2 sec 0.22 B 3 sec 0.31 A 4 sec 0.42 B 5 sec 0.53 A 6 sec 0.57 B 7 sec 0.67 A 8 sec 0.81 B 9 sec 0.9 A 10 sec 1 B

Device = ['A';'B'];Accuracy = [0.023;0.037];Tright = table(Device,Accuracy)

Tright=2×2 table Device Accuracy ______ ________ A 0.023 B 0.037

Merge the timetable and table. Device is the key variable because both Tleft and Tright have a variable with that name. T is a timetable.

T = join(Tleft,Tright)

T=10×3 timetable Time Measurements Device Accuracy ______ ____________ ______ ________ 1 sec 0.13 A 0.023 2 sec 0.22 B 0.037 3 sec 0.31 A 0.023 4 sec 0.42 B 0.037 5 sec 0.53 A 0.023 6 sec 0.57 B 0.037 7 sec 0.67 A 0.023 8 sec 0.81 B 0.037 9 sec 0.9 A 0.023 10 sec 1 B 0.037

Input Arguments

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`Tleft` — Left table
table | timetable

Left table, specified as a table or a timetable. For all key variables, each row of Tleft must match exactly one row in Tright.

`Tright` — Right table
table | timetable

Right table, specified as a table or a timetable. For all key variables, each row of Tright must match exactly one row in Tleft.

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: 'Keys',2 uses the second variable in Tleft and the second variable in Tright as key variables.

`Keys` — Variables to use as keys
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

Variables to use as keys, specified as the comma-separated pair consisting of 'Keys' and a positive integer, vector of positive integers, string array, character vector, cell array of character vectors, pattern scalar, or logical vector.

You cannot use the 'Keys' name-value pair argument with the 'LeftKeys' and 'RightKeys' name-value pair arguments.

The vector of row labels from an input table or timetable can be a key, alone or in combination with other key variables. Row labels are the row names of a table or the row times of a timetable. To use this vector as a key, specify it as 'Row' (for the row names of a table), as the name of a timetable vector of row times, or as the value of T.Properties.DimensionNames{1}, where T is the table or timetable.

For backward compatibility, you can also specify the value of 'Keys' as 'RowNames' when Tleft and Tright are tables with row names. However, the best practice is to specify the value of 'Keys' as the name of the vector of row names.

Example: 'Keys',[1 3] uses the first and third variables from Tleft and Tright as key variables.

Example: 'Keys',{'X','Y'} uses the variables named X and Y in Tleft and Tright as key variables.

Example: 'Keys','Row' uses the vectors of row names of Tleft and Tright as key variables, if both Tleft and Tright are tables with row names.

`LeftKeys` — Variables to use as keys in `Tleft`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

Variables to use as keys in Tleft, specified as the comma-separated pair consisting of 'LeftKeys' and a positive integer, vector of positive integers, string array, character vector, cell array of character vectors, pattern scalar, or logical vector.

You must use the 'LeftKeys' name-value pair argument in conjunction with the 'RightKeys' name-value pair argument. 'LeftKeys' and 'RightKeys' both must specify the same number of key variables. join pairs key values in Tleft and Tright based on their order.

Example: 'LeftKeys',1 uses only the first variable in Tleft as a key variable.

`RightKeys` — Variables to use as keys in `Tright`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

Variables to use as keys in Tright, specified as the comma-separated pair consisting of 'RightKeys' and a positive integer, vector of positive integers, string array, character vector, cell array of character vectors, pattern scalar, or logical vector.

You must use the 'RightKeys' name-value pair argument in conjunction with the 'LeftKeys' name-value pair argument. 'LeftKeys' and 'RightKeys' both must specify the same number of key variables. join pairs key values in Tleft and Tright based on their order.

Example: 'RightKeys',3 uses only the third variable in Tright as a key variable.

`LeftVariables` — Variables from `Tleft` to include in `T`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

Variables from Tleft to include in T, specified as the comma-separated pair consisting of 'LeftVariables' and a positive integer, vector of positive integers, string array, character vector, cell array of character vectors, pattern scalar, or logical vector.

You can use 'LeftVariables' to include or exclude key variables, as well as nonkey variables, from T. However, you cannot include row names or row times from Tleft, because they are not variables.

By default, join includes all variables from Tleft.

`RightVariables` — Variables from `Tright` to include in `T`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

Variables from Tright to include in T, specified as the comma-separated pair consisting of 'RightVariables' and a positive integer, vector of positive integers, string array, character vector, cell array of character vectors, pattern scalar, or logical vector.

You can use 'RightVariables' to include or exclude key variables, as well as nonkey variables, from T. However, you cannot include row names or row times from Tright, because they are not variables.

By default, join includes all variables from Tright except the key variables.

`KeepOneCopy` — Variables for which `join` retains only the copy from `Tleft`
string array | character vector | cell array of character vectors | `pattern` scalar

Variables for which join retains only the copy from Tleft, specified as the comma-separated pair consisting of 'KeepOneCopy' and a string array, character vector, cell array of character vectors, or pattern scalar that specifies variable names.

Key variables appear once in T, but if nonkey variables with identical names occur in Tleft and Tright, then join retains both copies in T by default. Use the 'KeepOneCopy' name-value pair to retain only the copy from Tleft.

Example: 'KeepOneCopy',Var2 keeps only the copy from Tleft of the nonkey variable Var2.

Output Arguments

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`T` — Merged data from `Tleft` and `Tright`
table | timetable

Merged data from Tleft and Tright, returned as a table or a timetable. The table, T, contains one row for each row in Tleft, appearing in the same order.

join creates T by horizontally concatenating Tleft(:,LeftVars) and Tright(iright,RightVars). By default, LeftVars is all the variables of Tleft, and RightVars is all the nonkey variables from Tright. Otherwise, LeftVars consists of the variables specified by the 'LeftVariables' name-value pair argument, and RightVars consists of the variables specified by the 'RightVariables' name-value pair argument.

If Tleft and Tright contain nonkey variables with the same name, join adds a unique suffix to the corresponding variable names in T, unless you specify the 'KeepOneCopy' name-value pair argument.

If Tleft is a table, then T is also a table. If Tleft is a timetable and Tright is either a timetable or a table, then T is a timetable.

You can store additional metadata in T, such as descriptions, variable units, variable names, and row names. For more information, see the Properties sections of table or timetable.

`iright` — Index to `Tright`
column vector

Index to Tright, returned as a column vector. Each element of iright identifies the row in Tright that corresponds to that row in the output table or timetable, T.

More About

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Key Variable

Variable used to match and combine data between input tables Tleft and Tright.

Key Value

Value in a key variable of Tleft or Tright.

Algorithms

The join function first finds one or more key variables. Then, join uses the key variables to find the row in input table Tright that matches each row in input table Tleft, and combines those rows to create a row in output table T.

If there is a one-to-one mapping between key values in Tleft and Tright, then join sorts the data in Tright and appends it to table Tleft.
If there is a many-to-one mapping between key values in Tleft and Tright, then join sorts and repeats the data in Tright before appending it to table Tleft.
If there is data in a key variable of Tright that does not map to a key value in Tleft, then join does not include that data in the output table, T.

Extended Capabilities

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

Usage notes and limitations:

To join a tall timetable and a tall table, the timetable must be the first input to join.
The values of these name-value arguments do not support pattern expressions:
- 'Keys'
- 'LeftKeys'
- 'RightKeys'
- 'LeftVariables'
- 'RightVariables'
- 'KeepOneCopy'

For more information, see Tall Arrays.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

In general, input tables cannot have nonkey variables with the same names. However, you can join subsets of the input tables if you specify the name-value arguments:
- 'KeepOneCopy', where you list variables to take from the left input table only.
- 'LeftVariables' and 'RightVariables', where you list variables to take from either the left input table or the right input table, but not both.
The values of these name-value arguments must be constant:
- 'Keys'
- 'LeftKeys'
- 'RightKeys'
- 'LeftVariables'
- 'RightVariables'
- 'KeepOneCopy'
The values of these name-value arguments do not support pattern expressions:
- 'Keys'
- 'LeftKeys'
- 'RightKeys'
- 'LeftVariables'
- 'RightVariables'
- 'KeepOneCopy'
Nested tables and timetables are not supported.

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

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Version History

Introduced in R2013b

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Combine two tables or timetables by rows using key variables (2024)

Syntax

Description

Examples

Append Values from One Table to Another

Merge Tables with One Variable in Common

Merge Tables by Specifying One Key Variable

Keep One Copy of Nonkey Variables

Merge Tables Using Row Names as Keys

Merge Tables Using Left and Right Keys

Merge Timetables

Merge Timetable and Table

Input Arguments

Tleft — Left table table | timetable

Tright — Right table table | timetable

Name-Value Arguments

Keys — Variables to use as keys positive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

LeftKeys — Variables to use as keys in Tleft positive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

RightKeys — Variables to use as keys in Tright positive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

LeftVariables — Variables from Tleft to include in Tpositive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

RightVariables — Variables from Tright to include in Tpositive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

KeepOneCopy — Variables for which join retains only the copy from Tleftstring array | character vector | cell array of character vectors | pattern scalar

Output Arguments

T — Merged data from Tleft and Trighttable | timetable

iright — Index to Tright column vector

More About

Key Variable

Key Value

Algorithms

Extended Capabilities

Tall Arrays Calculate with arrays that have more rows than fit in memory.

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

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

Version History

See Also

Functions

Live Editor Tasks

MATLAB-Befehl

Americas

Europe

Asia Pacific

`Tleft` — Left table
table | timetable

`Tright` — Right table
table | timetable

`Keys` — Variables to use as keys
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

`LeftKeys` — Variables to use as keys in `Tleft`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

`RightKeys` — Variables to use as keys in `Tright`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

`LeftVariables` — Variables from `Tleft` to include in `T`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

`RightVariables` — Variables from `Tright` to include in `T`
positive integer | vector of positive integers | string array | character vector | cell array of character vectors | `pattern` scalar | logical vector

`KeepOneCopy` — Variables for which `join` retains only the copy from `Tleft`
string array | character vector | cell array of character vectors | `pattern` scalar

`T` — Merged data from `Tleft` and `Tright`
table | timetable

`iright` — Index to `Tright`
column vector

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

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