Clear items from Memory in MATLAB

In this article, we are going to discuss "Clearing items from Memory", in MATLAB which can be done using clear operation. 

The clear operation is used to clear the specified items from memory or from the currently active workspace. It is used to free up the system memory.

Syntax:

clear

clear name1 ... nameN

clear -regexp expr1 ... exprN

clear('a', 'b', 'c')

clear(['a' 'b' 'c'])

clear functions

clear mex

clear global

clear all

clear keyword

Here,

• clear: This is used to remove all items from the current workspace.
• clear name1, ... nameN: This is used to remove the variables such as name1 ... nameN from memory.
• clear -regexp expr1 ... exprN: This is used to remove all variables matching any of the regular expressions listed. This is used to remove variables only.
• clear('a', 'b', 'c') and clear(['a' 'b' 'c']): This  is used to remove its variables if the specified variables exist in the local environment of the current function.
• clear functions: This is used to remove unlocked functions only. If a function is locked or currently running, it is not cleared from memory.
• clear mex: This is used to clear all MEX files from memory.
• clear global: This is used to clear all global variables.
• clear all: This is used to remove all variables, functions, and MEX files from memory.
• clear keyword: This is used to clear the items indicated by the keyword.

Example 1:

% MATLAB code for removes all the
% items so its output is blank.
% Initializing some items
A = 2;
B = 4;
C = 6;
D = 8;

% Calling the clear operation to
% clear all the above specified items
clear 

% Getting the remaining items
whos

 This example will clear all the values.

 Example 2: 

% MATLAB code for Clear operation
% Initializing some items
A = 2;
B = 4;
C = 6;
D = 8;

% Calling the clear operation to
% clear B and D items
clear B D;

% Getting the remaining items
whos

 Output:

Variables in the current scope:
  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
       A           1x1                          8  double
       C           1x1                          8  double
Total is 2 elements using 16 bytes

Example 3:

% MATLAB code for clear expression values
% Initializing some expressions
exp1 = 'ab+c';
exp2 = 'a-c';
exp3 = '+/gfg';

% Calling the clear operation to
% clear expression exp2
clear -regexp ^exp2;

% Getting the remaining expressions
whos

 Output:

Variables in the current scope:
  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
       exp1        1x4                          4  char
       exp3        1x5                          5  char
Total is 9 elements using 9 bytes

Example 4:

% MATLAB code for clear()
% Initializing some items
A = 2;
B = 4;
C = 6;
D = 8;

% Calling the clear function 
% to clear items A and C
clear ('A', 'C');

% Again calling the clear function
% to clear D items
clear (['D']);

% Getting the remaining items B
whos

 Output:

Variables in the current scope:
  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
       B           1x1                          8  double
Total is 1 element using 8 bytes

Example 5: 

% MATLAB code for clear global variable data
% Initializing some items
global A;
A = 2;
B = 4;
C = 6;
D = 8;

% Calling the clear function 
% to clear global items only
clear global

% Getting the remaining items
whos

 Output:

Variables in the current scope:
  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
       B           1x1                          8  double
       C           1x1                          8  double
       D           1x1                          8  double
Total is 3 elements using 24 bytes

Example 6:

% MATLAB code for clear value of variable
% Initializing some items
global A;
A = 2;
B = 4;
keyword = 6;
D = 8;

% Calling the clear function 
% to clear keyword items only
clear keyword

% Getting the remaining items
whos

 Output:

Variables in the current scope:
  Attr Name        Size                     Bytes  Class
  ==== ====        ====                     =====  =====
    g  A           1x1                          8  double
       B           1x1                          8  double
       D           1x1                          8  double
Total is 3 elements using 24 bytes

Example 7: 

% MATLAB code for all types of items are 
% cleared so nothing is printed as output.
% Initializing some items
global A; 
A = 2;
B = 4;
keyword = 6;
D = 8;

% Calling the clear function 
% to clear all items 
clear all

% Getting the remaining items
whos

 This example will clear all the values.