join
Combine two tables or timetables by rows using key variables
Description
combines the tables or timetables T
= join(Tleft
,Tright
)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
andTright
, if both inputs are tables, or ifTleft
is a timetable andTright
is a table.Vectors of row times, if both
Tleft
andTright
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, thenjoin
returnsT
as a table.If
Tleft
is a timetable, thenjoin
returnsT
as a timetable.
joins the tables or timetables with additional options specified by one or more
T
= join(Tleft
,Tright
,Name,Value
)Name,Value
pair arguments.
For example, you can specify which variables to use as key variables.
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(['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
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(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
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
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
,
where T
.Properties.DimensionNames{1}
is the table or
timetable.T
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.
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
,
where T
.Properties.DimensionNames{1}
is the table or
timetable.T
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.
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
,
where T
.Properties.DimensionNames{1}
is the table or
timetable.T
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
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
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
andTright
, thenjoin
sorts the data inTright
and appends it to tableTleft
.If there is a many-to-one mapping between key values in
Tleft
andTright
, thenjoin
sorts and repeats the data inTright
before appending it to tableTleft
.If there is data in a key variable of
Tright
that does not map to a key value inTleft
, thenjoin
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.
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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