Extracting one or more columns from a matrix in Matlab

In this lesson, I will explain how to extract one or more columns from a matrix (two-dimensional array) when using Matlab.

To illustrate this point, let me provide an example.

Create a 3x3 matrix in the Matlab session.

>> M = [ 1 2 3 ; 4 5 6 ; 7 8 9 ]
M =
1 2 3
4 5 6
7 8 9

This is a square matrix because it has the same number of rows and columns.

An example of a matrix

To extract the first column of the matrix, type M(:,1)

In the first parameter in parentheses, insert the colon symbol : to select all the rows in the matrix
In the second parameter, enter the integer 1 to select the first column of the matrix

>> M(:,1)

This way, you will extract all the elements that are present in the first column of the matrix.

ans =
1
4
7

The first column of the matrix

Now, type M(:,2) to extract the second column of the matrix.

In this case, you are indicating the number 2 in the second parameter because you want to select all the elements in the second column of the matrix.

>> M(:,2)
ans =
2
5
8

The second column of the matrix

Finally, type M(:,3) to extract the third column of the matrix:

>> M(:,3)
ans =
3
6
9

The third column of the matrix

If you want to extract only certain rows of a column, insert the range of rows you want to select in the first parameter.

For example, type M(1:2,3) to extract only the first two rows of the third column:

>> M(1:2,3)
ans =
3
6

The first and second row of the third column

When the rows you want to select are not contiguous, insert the list of rows in the second parameter between square brackets, separating them with a comma or space.

For example, type M([1 3],2) to extract the first and third row of the second column:

>> M([1 3],2)
ans =
2
8

The first and third row of the second column

In Matlab, you can also extract two or more columns from a matrix by specifying the range of columns to select in the second parameter of the command.

For example, M(:,1:2) extracts the first two columns of the matrix named "digita":

>> M(:,1:2)
ans =
1 2
4 5
7 8

which are the first two columns of the matrix.

To extract non-contiguous columns, you can specify a list of columns to extract in the second parameter, enclosed in square brackets and separated by a space or comma.

For example, type M(:,[1 3]) to extract the first and third columns of the matrix:

>> M([1 3],:)
ans =
1 3
4 6
7 9

which are the first and third columns of the matrix.

This command allows you to extract two or more columns of a matrix even if they are not contiguous.