join

Combine two tables or timetables by rows using key variables

Syntax

T = join(Tleft,Tright)

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

[T,iright] = join(___)

Description

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.

T = join(Tleft,Tright,Name=Value) specifies options using one or more name-value arguments in addition to the input arguments in the previous syntax. For example, you can specify which variables to use as key variables by setting Keys, LeftKeys, or RightKeys.

[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

Append Values from One Table to Another

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

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

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 Var2 from table Tleft.

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

Tright=5×2 table
    Var1    Var2
    ____    ____

     6       5  
     1       4  
     1       9  
     6       6  
     8       1  

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

T = join(Tleft,Tright,Keys="Var2")

T=5×4 table
    Var1_Tleft    Var2    Var3    Var1_Tright
    __________    ____    ____    ___________

        10         5       10          6     
         4         4        3          1     
         2         9        8          1     
         3         6        8          6     
         7         1        4          8     

join adds a unique suffix to the nonkey variable, Var1, to distinguish the data from tables Tleft and Tright.

Keep One Copy of Nonkey Variables

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

Create a table, Tleft.

Tleft = table([true;true;false;false;false],[38;43;38;40;49], ...
        VariableNames=["Smoker" "Age"], ...
        RowNames=["Sanchez" "Johnson" "Wu" "Jones" "Brown"])

Tleft=5×2 table
               Smoker    Age
               ______    ___

    Sanchez    true      38 
    Johnson    true      43 
    Wu         false     38 
    Jones      false     40 
    Brown      false     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; 149 87; 117 75; 154 93; 125 83], ...
         VariableNames=["Height" "Weight" "BloodPressure"], ...
         RowNames=["Brown" "Johnson" "Jones" "Sanchez" "Wu"])

Tright=5×3 table
               Height    Weight    BloodPressure
               ______    ______    _____________

    Brown        64       119       122     80  
    Johnson      69       163       149     87  
    Jones        67       133       117     75  
    Sanchez      71       176       154     93  
    Wu           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
               Smoker    Age    Height    Weight    BloodPressure
               ______    ___    ______    ______    _____________

    Sanchez    true      38       71       176       154     93  
    Johnson    true      43       69       163       149     87  
    Wu         false     38       64       131       125     83  
    Jones      false     40       67       133       117     75  
    Brown      false     49       64       119       122     80  

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

Merge Tables Using Left and Right Keys

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

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(Traffic,Noise,RowTimes=hours(1:5))

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(Distance,RowTimes=hours(1:5))

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

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(Measurements,Device,RowTimes=seconds(1:10))

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

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.

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 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 argument with the LeftKeys and RightKeys name-value 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 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 argument in conjunction with the RightKeys name-value 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.

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.

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 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 argument in conjunction with the LeftKeys name-value 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.

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.

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 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 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 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 KeepOneCopy to retain only the copy from Tleft.

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

Output Arguments

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 argument, and rightVars consists of the variables specified by the RightVariables name-value 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 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

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.

The join function supports tall arrays with the following usage notes and limitations:

• To join a tall timetable and a tall table, the timetable must be the first input to join.

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.

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Refer to the usage notes and limitations in the C/C++ Code Generation section. The same usage notes and limitations apply to GPU code generation.

Thread-Based Environment

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

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

Version History

Introduced in R2013b