MATLAB: How to locate and extract elements from a matrix

element extractionelement locationfor loop

Hi, I need to locate specific elements in each column of a matrix and print them in a new column matrix. For example if I have a 6×4 matrix

A = [a1 b1 c1 d1;
     a2 b2 c2 d2;
     a3 b3 c3 d3;
     a4 b4 c4 d4;
     a5 b5 c5 d5;
     a6 b6 c6 d6]

I should locate some elements from the first column of matrix A, and print them into two new column matrices B and C. The first column of matrix A is a1, a2, a3, a4, a5, a6

My new matrix B should take these elements: a1, a2, a3, a4, so

B = [a1; a2; a3; a4]

After that I should define new matrix C, which will take elements a3, a4, a5, a6, so

C = [a3; a4; a5; a6]

This process I need to repeat for every column of matrix A. Does anyone have tips how to do this? Thanks!

Best Answer

try this

clear all
close all
clc
    A=randint(6,4,[1 100])
    for i=1:size(A,2)
        o=A(:,i);
        B=o(1:4)'
        C=o(3:6)'
    end

Related Solutions

MATLAB: How to make a causal interleaver in the Communications Toolbox

Causal Interleaving is not available in Communications Toolbox, as a workaround you can write your own function that does this. If you re-arrange your input to be:

[a0 a1 a2 a3 a4 b0 b1 b2 b3 b4 c0 c1 c2 c3 c4] as :

input = [0 0 0 0 0; a0 a1 a2 a3 a4; b0 b1 b2 b3 b4; c0 c1 c2 c3 c4]

The output is:

 input =
 [  0,  0,   0,   0,    0 ]
 [ a0, a1, a2, a3, a4 ]
 [ b0, b1, b2, b3, b4]
 [ c0, c1, c2, c3, c4 ]

Then you truncate zeros of the first 3 columns, and c3 and c4 of the last 2 columns to get the following matrix:

 A1 =
 [ a0, a1, a2,  0,   0 ]
 [ b0, b1, b2, a3, a4]
 [ c0, c1, c2, b3, b4]

You can see that the output A0 0 A1 0 A2 B0 A3 B1 A4 B2 C0 B3 C1 B4 C2 ...is done by the following operations on the matrix A1:

1. Leaving the first column unchanged,

2. Replacing the second column with the fourth column,

3. Replacing the third column with second column,

4. The fourth column with the fifth column,

5. and the fifth column with the third column,

The output is:

 Output =
 [ a0,  0, a1,  0,  a2 ]
 [ b0, a3, b1, a4, b2]
 [ c0, b3, c1, b4, c2]

Note that you can use the following tips to get and change columns:

If input is A = [0 0 0 0 0; a0 a1 a2 a3; a4 b0 b1 b2 b3 b4; c0 c1 c2 c3 c4]

e1 = A(:,1); e2 = A(:,2)…to get columns of A

e1(1) = []; truncates the first element of the first column of A

e4(4) = []; truncates the last element of the last element of the last column of A

MATLAB: Outputting function into multiple columns of matrix

Instead of returning [A1, A2, A3, A4, A5, A6] seperatly redifine your function to return AA.

Where, AA = [A1 A2 A3 A4 A5 A6];

when assigning to a variable from a function which returns an array of values, variables are assigned to in order of the returned values.

For eg,

function [x, y] = func %a function

z = func; %assign return value of func to z

In this case z contains only the value of x.

This is the reason for your error.

If you are not allowed to change your function, you can do the following,

[A1, A2, A3, A4, A5, A6] = MyFun(M(:,[1:4 8:9],:) );

M(:,[1:4 8:9],:) = [A1 A2 A3 A4 A5 A6];

Best Answer

Related Solutions

MATLAB: How to make a causal interleaver in the Communications Toolbox

MATLAB: Outputting function into multiple columns of matrix

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