assignin

Assign value to variable in specified workspace

Syntax

assignin(ws,var,val)

Description

assignin(ws,var,val) assigns the value val to the variable var in the workspace ws. For example, assignin('base','x',42) assigns the value 42 to the variable x in the MATLAB^® base workspace.

If val requires evaluation, MATLAB evaluates it in the function that calls assignin, not in the workspace specified by ws. If val is a function handle, it must be evaluable in the function that calls assignin.

The assignin function is useful for these tasks:

• Exporting data from a function to the base workspace.

• From within a function, changing the value of a variable that is defined in the workspace of the caller function. For example, you can change the value of a variable in the calling-function argument list.

Examples

Update Base Workspace Variable from Function

In a file in your current working folder, create a function that adds two numbers and then assigns a value to a variable fcnStatus in the base workspace.

function c = myAdd(a,b)
    c = a+b;
    
    str = sprintf('%s called with %d,%d (%s)',mfilename,a,b,char(datetime));
    assignin('base','fcnStatus',str)
end

At the command prompt, call the function.

n = myAdd(2,3)

n =

     5

View the value of the fcnStatus variable that the myAdd function assigned in the base workspace.

fcnStatus

fcnStatus =

    'myAdd called with 2,3 (17-Nov-2017 14:56:14)'

Save Data from Dialog Box to Base Workspace

In a file in your current working folder, create a function that displays a dialog box to input a name and a birth year and computes age in the year 2050. The assignin function exports the values to the MATLAB workspace variables name and age2050.

function mydialog
    prompt = {'Enter name:','Enter birth year:'};
    answer = inputdlg(prompt);
    
    n = answer{1};
    birthyear = str2double(answer{2});
    a = 2050-birthyear;
    
    assignin('base','name',n);
    assignin('base','age2050',a);
end

At the command prompt, run the function, enter data, and click OK.

mydialog

View the exported values in the Workspace browser.

Change Value of Variable in Calling Function

Create a function that changes an input age to 42. The call to assignin in localfcn changes the value of a in the workspace of the main function, updateAge.

function updateAge(a)
    validateattributes(a,{'numeric'},{'scalar'})
    fprintf('\tYour age: %d\n',a)
    localfcn
    fprintf('\tYour updated age: %d\n',a)
end

function localfcn
    assignin('caller','a',42)
end

At the command prompt, call the main function.

updateAge(37)

	Your age: 37
	Your updated age: 42

While this example describes how to assign a variable into the caller workspace, the best practice is to have the local function localfcn return the updated age as an output argument.

Assign Function Handle to Variable in Specified Workspace

In a file in your current working folder, create a function that finds the minimum value of a random array. The assignfh local function assigns the function handle fh into the workspace of minRand. The minRand function evaluates fh with the input n.

function m = minRand(n)
    assignfh
    
    A = fh(n)
    m = min(A(:));
end

function assignfh
    fh = @(dim)rand(dim);
    assignin('caller','fh',fh)
end

Call the function with an input value of 2.

m = minRand(2)

A =

    0.3486    0.1423
    0.0419    0.0766


m =

    0.0419

The function handle evaluates to a 2-by-2 array of random numbers.

Create another version of the function, called minRand2, in which the local function overrides the rand function in the function handle definition.

Similar to the minRand example, the assignfh2 local function assigns fh into the workspace of minRand2. The assignfh2 function overrides the rand function in its workspace with a variable named rand and creates the function handle. This behavior is consistent with anonymous functions – the function handle is created using variables available at the time you create it. Therefore, the function handle evaluation in minRand2 results in n indexing into the rand array defined in assignfh2.

function m = minRand2(n)
    assignfh2(n)
    
    A = fh(n)
    m = min(A(:));
end

function assignfh2(n)
    rand = 13*ones(n);
    fh = @(dim)rand(dim);
    assignin('caller','fh',fh)
end

Call the function with an input value of 2.

m = minRand2(2)

A =

    13


m =

    13

When assigning an anonymous function to a caller workspace, MATLAB puts the definition of the function handle in a variable in the caller workspace. The function with the call to assignin evaluates the function handle. While this example describes how to assign a variable into the caller workspace, the best practice is to have the local function assignfh return the function handle as an output argument.

Input Arguments

ws — Workspace

'base' | 'caller'

Workspace, specified as 'base' or 'caller'.

To assign values in the MATLAB base workspace, use 'base'. The base workspace stores variables that you create at the MATLAB command prompt, including any variables that scripts create, assuming that you run the script from the command line or from the Editor.

To assign variables in the workspace of the caller function, use 'caller'. The caller workspace is the workspace of the function that called the currently running function. For example, assume that funA calls funB. The caller workspace of funB is funA. Therefore, from funB, you can assign a value to a variable in funA using assignin and specifying the workspace as 'caller'.

Note

Assigning to variables in the caller workspace can make code more difficult to understand, give surprising results to the user (unexpected or redefined variables in their workspace), and have a negative performance impact. The best practice is to have the function return the variables as output arguments.

The base and caller workspaces are equivalent in the following cases:

• You call a function at the command prompt and the main function calls assignin.

• You call assignin at the command prompt.

Data Types: char | string

var — Variable name

character vector | string scalar

Variable name, specified as a character vector or string scalar. If var does not exist in the specified workspace, the assignin function creates it.

Data Types: char | string

val — Value

scalar | array

Value of variable, specified as a scalar or array value. val can have any data type, and can include MATLAB expressions.

If the value of the variable requires evaluation, MATLAB evaluates the expression in the function that contains the call to assignin, not in the workspace specified by ws. If val is a function handle, it must be evaluable in the function that calls assignin.

Example: 5

Example: 'hello'

Example: rand(3,7)

Example: @cos

Tips

• The assignin function does not assign values to specific elements of an array. Therefore var cannot contain array indices. This code results in an error.

  X = 1:8;
  assignin('base','X(3:5)',-1);
  

  To assign values to specific elements of an array, use the evalin function.

  evalin('base','X(3:5) = -1')