convert matrix in single column

Hi, I have to convert a matrix in one column vector composed of all the columns of the original matrix. How can I do this? Thanks

[Sazzad Sayyed]

You can try matA=matA(:).This works.

[muhammad komugabe]

great. thanx

[Luke Handscomb]

This takes column1 and then appends column2 to the bottom of 1 and 3 to 2 and so on. What if I wanted to instead arrange it as row1+row2+row3....? Cheers

[Ndilokelwa Luis]

Transpose matrix first!

[Image Analyst]

You said "I have to convert a matrix in one column vector composed of all the columns of the original matrix." I thought you meant you had a column vector and had to convert it to a matrix having the same number of columns as the original matrix from where the column vector came. In other words, I thought you meant "I have to convert a matrix of one column vector INTO ONE composed of all the columns of the original matrix."

Seeing the answer you accepted, it appears that you actually meant "I have to convert a matrix INTO a one column vector that is composed of all the columns of the original matrix." Leaving out seemingly minor words completely changes the interpretation of the question, as does their placement in the sentence.

Answer 1

[Andrei Bobrov]

yourvector = yourmatrix(:);

[muhammad komugabe]

wow. it works fine

[sayyam khurana]

NOT ALL HEROS WEAR CAPES.

[Akash Singh]

I know it works fine, but how?

[James Tursa]

Because (:) is the syntax in MATLAB for turning a variable into a column.

[Mihai Gabriel Calitescu]

A man with this much power in his bare hands... im scared

[Farid]

WOW

[Pablo Moreno Galbis]

Drops the mic.

[Paúl Aguilar]

Excelente, thanks sir.

[rishika yadav]

HOW WE RESHAPE THE MATRIX WITH DIFFERENT ROW NO, AND SAME COLUMBS

[Image Analyst]

@rishika yadav you can use interp2 to interpolate a different height:

m = reshape(1:18, [], 3) % Create 6 row by 3 column sample data
[oldHeight, columns] = size(m)
% Make the matrix taller by interpolating.
newHeight = 8;
[xq,yq] = meshgrid(1:columns, linspace(1, oldHeight, newHeight));
mTaller = interp2(m, xq, yq)
fprintf('The size of mTaller is %d rows by %d columns.\n\n', size(mTaller, 1), size(mTaller, 2))
% Make the matrix taller by interpolating.
newHeight = 3;
[xq,yq] = meshgrid(1:columns, linspace(1, oldHeight, newHeight));
mShorter = interp2(m, xq, yq)
fprintf('The size of mShorter is %d rows by %d columns.\n', size(mShorter, 1), size(mShorter, 2))

The first/top and last/bottom rows will have the same values, and more, or fewer, rows will be interpolated in between the top row and bottom row so that you have your new desired height.

Answer 2

[Kyril Kaufmann]

For a more algorithmic solution:

% From matrix to vector
N   = 10;
mat1 = rand(N);
vec1 = zeros(N*N,1);
for i=1:N
    for j=1:N
        vec1((i-1)*N + j) = mat1(i,j);
    end
end

% From vector to matrix
N   = 10;
vec2 = rand(N*N,1);
mat2 = zeros(N);
for i=1:N
    for j=1:N
        mat2(i,j) = vec2((i-1)*N + j);
    end
end

Answer 3

[Image Analyst]

If your column vector was "composed of all the columns of the original matrix", then use the reshape() command to turn it from a column vector back into the original 2D matrix.

matrix2D = reshape(columnVector, [rows columns]);

(The converse, how to get the column vector in the first place (what you may have done to get your vector) is accomplished like this columnVector = fullMatrix(:).)

[yang liu]

hey, I want to know which is faster? command 'reshape()' or '(:)', are they two do the job based on the same underlying code? Thanks, I'm try to get my code running faster.

[Image Analyst]

I would guess that (:) is faster, but they're going in opposite directions. Just use tic and toc a bunch of times to test it and see.

[Akash Singh]

How is (:) working? I'm trying to understand the steps behind this method.

[James Tursa]

This has already been answered. The reason (:) turns a variable into a column is because MATLAB is programmed that way. That's what this particular syntax does. No other reason. There are no "steps" behind it. It is the equivalent of reshape(your_variable,numel(your_variable),1);

[Wolfgang Klassen]

Matlab has multiple kinds of indexing, and which one gets used is often a function of how many indices you use. A(2,3) accesses the element in the second row, third column. A(6) accesses the sixth element in the matrix, starting numbering in the first column and going down the columns until you get to the end. Just like you might say A(1,:) accesses all the columns in the first row, A(:) accesses all the elements in that ordering scheme, which happens to be all the elements in the matrix, in a particular order. If you wanted a different order, you'd have to use reshape, or maybe transpose it first.

[Surya Kanthi]

I dont know but I have a 1056x2 matrix and it does not work, any clue?

[James Tursa]

Please post a new Question with the details of your problem.

Answer 4

[Rifat Hossain]

columnvector=matrix(:) this work fine

Answer 5

[AMIR KHFAGI]

Hi, I have to convert one column vector to a matrix in matlab. How can I do this?

[Shuyun Yuan]

reshape function