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 arrays with the same number of rows each time it is called. The ith variable in the output argument, B{:,i}, is equal to func(A{:,i}).

If A is a timetable and func aggregates data over groups of rows, then varfun assigns the first row time from each group of rows in A as the corresponding row time in B. To return B as a table without row times, specify 'OutputFormat' as 'table'.

B = varfun(func,A,Name,Value) applies the function func separately to each variable of the table or timetable A with additional options specified by one or more Name,Value pair arguments.

For example, you can specify which variables to pass to the function.

Examples

Apply Element-wise Function

Define and apply an element-wise function to the variables of a table to square all the elements.

Define a table containing 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

Define the anonymous function to find the square of an input.

func = @(x) x.^2;

Apply the function to all the variables of table A.

B = varfun(func,A)

B=5×2 table
    Fun_Var1    Fun_Var2
    ________    ________

     0.5041      0.0529 
     4.2025      0.0144 
     0.1225      0.0324 
     0.6724      0.0529 
     2.4649      0.1681 

The variables of B have names based on the function and the variable names from A.

Apply Function that Returns Scalar From Vector

Compute the mean of each variable in a 5-by-2 table.

Define a table containing 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

Define the anonymous function to find the mean of an input.

func = @mean;

func uses an existing MATLAB® function to define the operation.

Apply the function to all the variables of table A.

B = varfun(func,A)

B=1×2 table
    mean_Var1    mean_Var2
    _________    _________

     -0.188        0.162  

B is a table containing the average value from each variable. To return a numeric vector instead of a table, you can use B = varfun(func,A,'OutputFormat','uniform').

Apply Function to Groups Within Variables

Compute the group-wise means of variables in a table, A, and return them as rows in a table, B.

Create a table where one variable defines groups.

A = table({'test2';'test1';'test2';'test3';'test1'},...
    [0.71;-2.05;-0.35;-0.82;1.57],[0.23;0.12;-0.18;0.23;0.41])

A=5×3 table
      Var1       Var2     Var3 
    _________    _____    _____

    {'test2'}     0.71     0.23
    {'test1'}    -2.05     0.12
    {'test2'}    -0.35    -0.18
    {'test3'}    -0.82     0.23
    {'test1'}     1.57     0.41

Define the anonymous function to find the mean of an input.

func = @mean;

func uses an existing MATLAB® function to define the operation.

Apply the function to each group of data defined by Var1.

B = varfun(func,A,'GroupingVariables','Var1')

B=3×4 table
      Var1       GroupCount    mean_Var2    mean_Var3
    _________    __________    _________    _________

    {'test1'}        2           -0.24        0.265  
    {'test2'}        2            0.18        0.025  
    {'test3'}        1           -0.82         0.23  

B contains a variable called GroupCount to indicate the number of entries from table A in that group.

Apply Function to Groups Within Timetable Variables

Create a timetable containing sample data. The row times of the timetable also define groups.

dt = datetime(2016,1,1)+days([0 1 1 2 3 3])';
A = timetable(dt,[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
        dt           x        y  
    ___________    _____    _____

    01-Jan-2016     0.71     0.23
    02-Jan-2016    -2.05     0.12
    02-Jan-2016    -0.35    -0.18
    03-Jan-2016    -0.82     0.23
    04-Jan-2016     1.57     0.41
    04-Jan-2016     0.09     0.02

Compute the group-wise means of the variables in the timetable. varfun returns B as a timetable because A is a timetable. When you specify the row times as the grouping variable, you cannot specify any variable as another grouping variable.

B = varfun(@mean,A,'GroupingVariables','dt')

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

    01-Jan-2016        1          0.71      0.23 
    02-Jan-2016        2          -1.2     -0.03 
    03-Jan-2016        1         -0.82      0.23 
    04-Jan-2016        2          0.83     0.215 

Input Arguments

func — Function

function handle

Function, specified as a function handle. You can define the function in a file or as an anonymous function. 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.

Use the 'OutputFormat','cell' name-value pair argument, if the function func take one input argument and returns arrays with a different numbers of rows each time it is called. Otherwise, func must return arrays with the same number of rows.

Example: func = @(x) x.^2; computes the square of each element of an input.

A — Input table

table | timetable

Input table, specified as a table or a timetable.

Name-Value Pair Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Example: 'InputVariables',2 uses only the second variable in A as an input to func.

'InputVariables' — Specifiers for selecting variables of A to pass to func

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

Specifiers for selecting variables of A to pass to func, specified as the comma-separated pair consisting of 'InputVariables' and a positive integer, vector of positive integers, character vector, cell array of character vectors, string array, logical vector, or a function handle.

If you specify 'InputVariables' as a function handle, then it must return a logical scalar, and varfun passes only the variables in A where the function returns 1 (true).

'GroupingVariables' — One or more variables in A that define groups of rows

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

One or more variables in A that define groups of rows, specified as the comma-separated pair consisting of 'GroupingVariables' and a positive integer, vector of positive integers, character vector, cell array of character vectors, string array, or logical vector.

The value of 'GroupingVariables' specifies which table variables are the grouping variables, not their data types. A grouping variable can be numeric, or have data type categorical, calendarDuration, datetime, duration, logical, or string.

Rows in A that have the same grouping variable values belong to the same group. varfun applies func to each group of rows within each of the variables of A, rather than to each entire variable.

If any grouping variable contains NaNs or missing values (such as NaTs, undefined categorical values, or missing strings), then the corresponding rows do not belong to any group, and are excluded from the output.

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 when you specify 'OutputFormat','uniform' or 'OutputFormat','cell'. When you specify 'OutputFormat','table' or 'OutputFormat','timetable', the sizes of the outputs from func determine how many rows of B correspond to each group.

'OutputFormat' — Format of B

'table' (default) | 'timetable' | 'uniform' | 'cell'

Format of B, specified as the comma-separated pair consisting of 'OutputFormat' and either the value 'uniform', 'table', 'timetable', or 'cell'.

'table'	varfun returns a table with one variable for each variable in A (or each variable specified with 'InputVariables'). For grouped computation, B, also contains the grouping variables. '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 computation, func must return arrays with the same number of rows each time it is called. For grouped computation, func must return values with the same number of rows each time it is called for a given group. If A is a table, then this 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 computation, B also contains the grouping variables. 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 the output format as 'OutputFormat','table'. If A is a timetable, then this is the default output format.
'uniform'	varfun concatenates the values into a vector. func must return a scalar with the same data type each time it is called.
'cell'	varfun returns B as a cell array. 'cell' allows you to use a function that returns values of different sizes or data types.

'ErrorHandler' — Function to call if func fails

function handle

Function to call if func fails, specified as the comma-separated pair consisting of 'ErrorHandler' and a function handle. Define this function so that it rethrows the error or returns valid outputs for function func.

MATLAB calls the specified error-handling function with two input arguments:

• A structure with these fields:

  identifier	Error identifier.
  message	Error message text.
  index	Index of the variable for which the error occurred.
  name	Name of the variable for which the error occurred.

• The set of input arguments to function func at the time of the error.

For example,

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

Output Arguments

B — Output table

table | timetable

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

Extended Capabilities

Tall Arrays

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

This function supports tall arrays with the limitations:

• The func input must always return a tall array.

• Supported name-value pairs are:

  • 'InputVariables' — Cannot be specified as a function handle.

  • 'OutputFormat' — Value can be 'uniform', 'table', 'timetable', or 'cell' only.

• When the input array is a tall timetable and 'OutputFormat' is 'timetable', 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 '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 the value of '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.