CODEWITHSUNDEEP
matlab
zebra
zebra

Reputation: 6531

What does x = x(:) mean in matlab, where x is a vector?

This is a hard question to google. I am new to Matlab and have seen the following statement, but I can't see how it does anything. What doe x = x(:) do?

Upvotes: 12

Views: 33993

Answers (7)

Trig
Trig

Reputation: 31

This operator tells matlab to try to convert the data type also.

For example:

Both data types set as disparate types:

>> foo = uint8(0);

>> bar = double(0);

Check data types with "whos" command:

>> whos foo bar
  Name      Size            Bytes  Class     Attributes

  bar       1x1                 8  double              
  foo       1x1                 1  uint8

Assign the uint8 into the double with the (:) operator:

>> bar(:) = foo;

and it remains a double

>> whos foo bar
  Name      Size            Bytes  Class     Attributes

  bar       1x1                 8  double              
  foo       1x1                 1  uint8

assign the double with a unit8 without the (:) operator :

>> bar = foo;

and it changes to a uint8 data type:

>> whos foo bar
  Name      Size            Bytes  Class     Attributes

  bar       1x1                 8  uint8      
  foo       1x1                 1  uint8

Upvotes: 1

Arun
Arun

Reputation: 75

If x is a matrix, like the following: a 3*3 matrix,

    x=[1,2,3;4,5,6;7,8,9];
    x=x(:);

The statement x=x(:) lists the matrix as a column vector. The output would be

    1
    2
    3
    4
    5
    6
    7
    8    
    9

The same is what is obtained when x is a row vector.

so in general, x(:) lists the elements of x as column vector.

Upvotes: 1

user85109
user85109

Reputation:

As others have said, x(:) converts x into a vector, a column vector specifically. The point is that it makes your code robust to the user supplying a row vector my accident. For example,

x = 1:5;

has created a ROW vector. Some operations will require a column vector. Since x(:) does nothing to a vector that is already a column vector, this is a way of writing robust, stable code.

Of course, if x was a 3x4 matrix, it will still convert x into a column vector of length 12, so the best code needs to test for things like that, if it is a problem.

Upvotes: 2

Óscar López
Óscar López

Reputation: 236034

This syntax is generally used to ensure that x is a column vector:

x = x(:)

Similarly, this line ensures that x is a row vector

x = x(:)'

Upvotes: 2

voidengine
voidengine

Reputation: 2579

x(:) transforms the array to a column vector.

More about the colon operator

Upvotes: 2

Tim
Tim

Reputation: 14446

x(:) reshapes your matrix.

Thereby, if your matrix is

1 2 3
5 6 7
8 9 10

calling x=x(:) sets x to

1
5
8 
2
6
9
3
7
10

Upvotes: 1

Oliver Charlesworth
Oliver Charlesworth

Reputation: 272557

: is the colon operator. In this context, it reshapes x to a one-dimensional column vector.

So this code:

x = [ 1 3
      2 4 ];

x = x(:);

disp(x)

results in:

1
2
3
4

Upvotes: 15

Related Questions