varfun

Apply function to table or timetable variables

Syntax

B = varfun(func,A)

B = varfun(func,A,Name,Value)

Description

B = varfun(func,A) applies the function func separately to each variable of the table or timetable A and returns the results in the table or timetable B.

The function func must take one input argument and return an array with the same number of rows each time it is called. The ith value in the output argument, B{:,i}, is equal to func(A{:,i}).

B = varfun(func,A,Name,Value) specifies options using one or more name-value arguments. For example, you can use the GroupingVariables name-value argument to perform calculations on groups of data within table variables. For more information about calculations on groups of data, see Calculations on Groups of Data.

Examples

Apply Element-Wise Function

Apply an element-wise function to the variables of a table.

Create a table that contains numeric variables.

A = table([10.71;-2.05;-0.35;-0.82;1.57],[9.23;3.12;-1.18;0.23;16.41])

A=5×2 table
    Var1     Var2 
    _____    _____

    10.71     9.23
    -2.05     3.12
    -0.35    -1.18
    -0.82     0.23
     1.57    16.41

Round the numeric values in A by applying the round function. To specify a function as an input argument to varfun, use the @ symbol. The variable names of the output table are based on the function name and the variable names from the input table.

B = varfun(@round,A)

B=5×2 table
    round_Var1    round_Var2
    __________    __________

        11             9    
        -2             3    
         0            -1    
        -1             0    
         2            16    

Apply Function That Reduces Table Variables

You can apply a function, such as sum or max, that reduces table variables along the first dimension. For example, use varfun to calculate the mean of each variable in a table.

Create a table that contains numeric variables.

A = table([0.71;-2.05;-0.35;-0.82;1.57],[0.23;0.12;-0.18;0.23;0.41])

A=5×2 table
    Var1     Var2 
    _____    _____

     0.71     0.23
    -2.05     0.12
    -0.35    -0.18
    -0.82     0.23
     1.57     0.41

Apply the mean function to all the variables of the table. The output table contains the mean value of each variable of the input table.

B = varfun(@mean,A)

B=1×2 table
    mean_Var1    mean_Var2
    _________    _________

     -0.188        0.162  

To have varfun return a numeric vector instead of a table, specify the OutputFormat name-value argument as "uniform". To use the "uniform" output format, func must always return a scalar.

B = varfun(@mean,A,"OutputFormat","uniform")

B = 1×2

   -0.1880    0.1620

Apply Function to Groups Within Variables

Create a table that has numeric data variables and a nonnumeric variable that is a grouping variable. Then perform a calculation on each group within the numeric variables.

Read data from a CSV (comma-separated values) file into a table. The sample file contains test scores for 10 students from two different schools.

scores = readtable("testScores.csv","TextType","string");
scores.School = categorical(scores.School)

scores=10×5 table
     LastName       School      Test1    Test2    Test3
    __________    __________    _____    _____    _____

    "Jeong"       XYZ School     90       87       93  
    "Collins"     XYZ School     87       85       83  
    "Torres"      XYZ School     86       85       88  
    "Phillips"    ABC School     75       80       72  
    "Ling"        ABC School     89       86       87  
    "Ramirez"     ABC School     96       92       98  
    "Lee"         XYZ School     78       75       77  
    "Walker"      ABC School     91       94       92  
    "Garcia"      ABC School     86       83       85  
    "Chang"       XYZ School     79       76       82  

Calculate the mean score for each test by school. The variables Test1, Test2, and Test3 are the numeric data variables. The School variable is the grouping variable. When you specify a grouping variable, its unique values define groups that corresponding values in the data variables belong to.

vars = ["Test1","Test2","Test3"];
meanScoresBySchool = varfun(@mean, ...
                            scores, ...
                            "InputVariables",vars, ...
                            "GroupingVariables","School")

meanScoresBySchool=2×5 table
      School      GroupCount    mean_Test1    mean_Test2    mean_Test3
    __________    __________    __________    __________    __________

    ABC School        5            87.4            87          86.8   
    XYZ School        5              84          81.6          84.6   

The output table includes a variable named GroupCount to indicate the number of rows from the input table in that group.

Apply Function to Groups Within Timetable Variables

Create a timetable containing sample data. The row times of the timetable can define groups because row times can be duplicates.

Timestamps = datetime(2023,1,1)+days([0 1 1 2 3 3])';
A = timetable(Timestamps, ...
              [0.71;-2.05;-0.35;-0.82;1.57;0.09], ...
              [0.23;0.12;-0.18;0.23;0.41;0.02], ...
              'VariableNames',["x","y"])

A=6×2 timetable
    Timestamps       x        y  
    ___________    _____    _____

    01-Jan-2023     0.71     0.23
    02-Jan-2023    -2.05     0.12
    02-Jan-2023    -0.35    -0.18
    03-Jan-2023    -0.82     0.23
    04-Jan-2023     1.57     0.41
    04-Jan-2023     0.09     0.02

Compute the mean values of the variables in the timetable by day. Specify the vector of row times as the grouping variable. The output B is a timetable because the input A is a timetable. When you specify the vector of row times as the grouping variable, you cannot specify any variable as another grouping variable.

B = varfun(@mean,A,"GroupingVariables","Timestamps")

B=4×3 timetable
    Timestamps     GroupCount    mean_x    mean_y
    ___________    __________    ______    ______

    01-Jan-2023        1          0.71      0.23 
    02-Jan-2023        2          -1.2     -0.03 
    03-Jan-2023        1         -0.82      0.23 
    04-Jan-2023        2          0.83     0.215 

Pass Optional Arguments to Applied Function

To pass optional arguments when you apply a function, wrap the function call in an anonymous function.

Create a table that contains numeric variables. Assign NaN to some elements of the table.

A = table([10.71;-2.05;NaN;-0.82;1.57],[9.23;NaN;-1.18;0.23;16.41])

A=5×2 table
    Var1     Var2 
    _____    _____

    10.71     9.23
    -2.05      NaN
      NaN    -1.18
    -0.82     0.23
     1.57    16.41

By default, the mean function returns NaN when input arrays have NaNs.

B = varfun(@mean,A)

B=1×2 table
    mean_Var1    mean_Var2
    _________    _________

       NaN          NaN   

To omit NaNs when you apply mean, specify the "omitnan" option. To use this option when you apply mean, wrap a call that specifies "omitnan" in an anonymous function.

func = @(x) mean(x,"omitnan");

Calculate the mean values with "omitnan" by applying the anonymous function.

C = varfun(func,A)

C=1×2 table
    Fun_Var1    Fun_Var2
    ________    ________

     2.3525      6.1725 

Input Arguments

func — Function

function handle

Function, specified as a function handle. You can specify a handle for an existing function, define the function in a file, or specify an anonymous function. The function takes one input argument and must have a syntax in this form:

result = f(arg)

To call f on the variables of A, specify func as shown in this call to varfun.

func = @f;
B = varfun(func,A);

For every variable in A, varfun calls func on that variable, and then assigns the output of func as the corresponding variable in output B.

Some further considerations:

• The function that func represents can have other syntaxes with additional optional arguments. But when varfun calls the function, it calls the syntax that has only one input argument.

  For example, the mean function has syntaxes that specify optional arguments, such as "omitnan". But if you specify func as @mean, then varfun calls mean using the mean(arg) syntax.

• To call a function with optional arguments, wrap it in an anonymous function. For example, to call mean with the "omitnan" option, specify func as @(x) mean(x,"omitnan").

• If func returns an array with a different number of rows each time it is called, then specify the OutputFormat name-value argument as "cell". Otherwise, func must return an array with the same number of rows each time it is called.

• If func corresponds to more than one function file (that is, if func represents a set of overloaded functions), MATLAB^® determines which function to call based on the class of the input arguments.

Example: B = varfun(@mean,A) calculates the mean value of an input.

Example: B = varfun(@(x) x.^2,A) calculates the square of each element of an input.

Example: B = varfun(@(x) mean(x,"omitnan"),A) calls mean with the "omitnan" option specified.

A — Input table

table | timetable

Input table, specified as a table or timetable.

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: B = varfun(func,A,InputVariables=["Var2","Var3"]) uses only the variables named Var2 and Var3 in A as the inputs to func.

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

Example: B = varfun(func,A,"InputVariables",["Var2","Var3"]) uses only the variables named Var2 and Var3 in A as the inputs to func.

InputVariables — Variables of A to pass to func

positive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector | function handle

Variables of A to pass to func, specified using one of the indexing schemes from this table.

Indexing Scheme	Examples
Variable names: A string array, character vector, or cell array of character vectors A pattern object	"A" or 'A' — A variable named A ["A","B"] or {'A','B'} — Two variables named A and B "Var"+digitsPattern(1) — Variables named "Var" followed by a single digit
Variable index: An index number that refers to the location of a variable in the table A vector of numbers A logical vector. Typically, this vector is the same length as the number of variables, but you can omit trailing 0 or false values	3 — The third variable from the table [2 3] — The second and third variables from the table [false false true] — The third variable
Function handle: A handle to a function that takes one argument as input and returns a logical scalar. The function must have a syntax in this form: tf = f(arg) If you need to apply a function that has additional optional arguments, wrap it in an anonymous function.	@isnumeric — Handle to a function that returns true for an input argument that contain numeric values

Example: B = varfun(func,A,InputVariables=[1 3 4]) uses only the first, third, and fourth variables in A as the inputs to func.

Example: B = varfun(func,A,InputVariables=@isnumeric) uses only the numeric variables in A as the inputs to func.

GroupingVariables — Variables of A to use as grouping variables

positive integer | vector of positive integers | string array | character vector | cell array of character vectors | pattern scalar | logical vector

Variables of A to use as grouping variables, specified using one of the indexing schemes from this table.

Indexing Scheme	Examples
Variable names: A string array, character vector, or cell array of character vectors A pattern object	"A" or 'A' — A variable named A ["A","B"] or {'A','B'} — Two variables named A and B "Var"+digitsPattern(1) — Variables named "Var" followed by a single digit
Variable index: An index number that refers to the location of a variable in the table A vector of numbers A logical vector. Typically, this vector is the same length as the number of variables, but you can omit trailing 0 or false values	3 — The third variable from the table [2 3] — The second and third variables from the table [false false true] — The third variable

The unique values in the grouping variables define groups. Rows in A where the grouping variables have the same values belong to the same group. varfun applies func to each group of rows within each of the remaining variables of A, rather than to entire variables. For more information on calculations using grouping variables, see Calculations on Groups of Data.

Grouping variables can have any of the data types listed in this table.

Values That Specify Groups	Data Type of Grouping Variable
Numbers	Numeric or logical vector
Text	String array or cell array of character vectors
Dates and times	datetime, duration, or calendarDuration vector
Categories	categorical vector
Bins	Vector of binned values, created by binning a continuous distribution of numeric, datetime, or duration values

Many data types have ways to represent missing values, such as NaNs, NaTs, undefined categorical values, or missing strings. If any grouping variable has a data type that can represent missing values, then rows where missing values occur in that grouping variable do not belong to any group and are excluded from the output.

To include rows where the grouping variables have missing values, consider using the groupsummary function instead.

Row labels can be grouping variables. You can group on row labels alone, on one or more variables in A, or on row labels and variables together.

• If A is a table, then the labels are row names.

• If A is a timetable, then the labels are row times.

The output B has one row for each group of rows in the input A. If B is a table or timetable, then B has:

• Variables corresponding to the input table variables that func was applied to

• Variables corresponding to the grouping variables

• A new variable, GroupCount, whose values are the number of rows of the input A that are in each group

If B is a timetable, then B also has:

• Row times, where the first row time from each group of rows in A is the corresponding row time in B. To return B as a table without row times, specify OutputFormat as "table".

Example: B = varfun(func,A,GroupingVariables="Var3") uses the variable named Var3 in A as a grouping variable.

Example: B = varfun(func,A,GroupingVariables=["Var3","Var4"]) uses the variables named Var3 and Var4 in A as grouping variables.

Example: B = varfun(func,A,GroupingVariables=[3 4]) uses the third and fourth variables in A as grouping variables.

OutputFormat — Format of B

"auto" (default) | "table" | "timetable" | "uniform" | "cell"

Format of B, specified as one of the values in this table.

"auto" (default) (since R2023a)	varfun returns an output whose data type matches the data type of the input A.
"table"	varfun returns a table with one variable for each variable in A (or each variable specified with InputVariables). For grouped calculations, B also contains the grouping variables and a new GroupCount variable. "table" allows you to use a function that returns values of different sizes or data types for the different variables in A. However, for ungrouped calculations, func must return an array with the same number of rows each time it is called. For grouped calculations, func must return an array with the same number of rows each time it is called for a given group. If A is a table, then this format is the default output format.
"timetable"	varfun returns a timetable with one variable for each variable in A (or each variable specified with InputVariables). For grouped calculations, B also contains the grouping variables and a new GroupCount variable. varfun creates the row times of B from the row times of A. If the row times assigned to B do not make sense in the context of the calculations performed using func, then specify OutputFormat as "table". If A is a timetable, then this format is the default output format.
"uniform"	varfun concatenates the output values into a vector. func must return a scalar with the same data type each time it is called.
"cell"	varfun returns a cell array. "cell" allows you to use a function that returns values of different sizes or data types.

Example: B = varfun(func,A,OutputFormat="uniform") returns the output as a vector.

ErrorHandler — Function to call if func fails

function handle

Function to call if func fails, specified as a function handle. If func throws an error, then the error handler function specified by ErrorHandler catches the error and takes the specified action.

The error handler function must meet these requirements:

• The definition of the error handler function must specify that it returns output arguments that match the number and data types of the output arguments of func.

  When called, the error handler function can either throw an error or return output arguments. But even if the error handler always throws an error, its definition must specify that it returns the same types and number of output arguments as func.

• The error handler function cannot be an anonymous function.

  Instead, write it as a local function. You can even define a local function in a script. You do not have to write the local function in a separate file.

If you do not specify ErrorHandler, then varfun rethrows the error that it caught from func.

The first input argument of the error handler is a structure with these fields:

• cause — MException object that contains information about the error (since R2024a)

• index — Index of the variable where the error occurred

• name — Name of the variable where the error occurred

The remaining input arguments to the error handler are the input arguments for the call to func that made func throw the error.

For example, suppose that func returns two doubles as output arguments. You can specify the error handler as a function that raises a warning and returns two output arguments.

function [A,B] = errorFunc(S,varargin)
    warning(S.cause.identifier,S.cause.message);
    A = NaN;
    B = NaN;
end

In releases before R2024a, the first input argument of the error handler is a structure with these fields:

• identifier — Error identifier

• message — Error message text

• index — Index of the variable where the error occurred

• name — Name of the variable where the error occurred

Example: B = varfun(func,A,ErrorHandler=@errorFunc) specifies errorFunc as the error handler.

Output Arguments

B — Output values

table | timetable | cell array | vector

Output values, returned as a table, timetable, cell array, or vector.

If B is a table or timetable, then it can store metadata such as descriptions, variable units, variable names, and row names. For more information, see the Properties sections of table or timetable.

To return B as a cell array or vector, specify the OutputFormat name-value argument.

More About

Calculations on Groups of Data

In data analysis, you commonly perform calculations on groups of data. For such calculations, you split one or more data variables into groups of data, perform a calculation on each group, and combine the results into one or more output variables. You can specify the groups using one or more grouping variables. The unique values in the grouping variables define the groups that the corresponding values of the data variables belong to.

For example, the diagram shows a simple grouped calculation that splits a 6-by-1 numeric vector into two groups of data, calculates the mean of each group, and then combines the outputs into a 2-by-1 numeric vector. The 6-by-1 grouping variable has two unique values, AB and XYZ.

You can specify grouping variables that have numbers, text, dates and times, categories, or bins.

Extended Capabilities

Tall Arrays

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

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

• The func input must always return a tall array.

• Supported name-value arguments are:

  • InputVariables — Value cannot be a function handle.

  • OutputFormat

• When the input array is a tall timetable and OutputFormat is "timetable" or "auto", the specified function must return an array with the same size in the first dimension as the input. Specify OutputFormat as "table" when the input function is a reduction function such as mean.

For more information, see Tall Arrays.

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• The function handle input, func, must be constant.

• While function handles can be inputs to varfun itself, they cannot be inputs to your entry point functions. Specify func within the code meant for code generation. For more information, see Function Handle Limitations for Code Generation (MATLAB Coder).

• The values for all name-value arguments must be constant.

• The values of the InputVariables and GroupingVariables name-value arguments do not support pattern expressions.

• The ErrorHandler name-value argument is not supported for code generation.

• Variable-size input arguments are not supported.

• Grouping variables cannot have duplicate values in generated code.

• You cannot specify OutputFormat as "cell" if you specify the GroupingVariables name-value argument and the function returns a different data type for each variable specified by InputVariables.

• If the input is a timetable and you specify GroupingVariables, then the output is always an irregular timetable.

• If you specify groups and the number of groups is not known at compile time, and that number is zero, then empty double variables in the output might have sizes of 1-by-0 in generated code. In MATLAB, such variables have sizes of 0-by-0.

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

Version History

Introduced in R2013b

R2023a: Match output data type to input data type by specifying the OutputFormat name-value argument as "auto"

To return an output whose data type matches the data type of the input, specify the OutputFormat name-value argument as "auto". This value is the default value.