Splitting Up Large Matrix into n rows x 2 columns

I have a large matrix with n rows and 4 columns. I need to split the four columns into two separate matricies (each n rows by 2 columns) so that they can later be graphed x vs y.

Data sample:

Time Money Time Money

1 30 6 100

2 40 7 110

3 50 8 120

Ideally, I'd like this to be done for n rows and n columns, forming n number of smaller arrays. Any ideas? I saw similar questions, however the matricies were split with a set sized matrix, whereas the size of my matrix may change.

Answer 1

[Fangjun Jiang]

n=100;
a=rand(100,4);
x=a(:,1:2)
y=a(:,3:4)

Answer 2

[Rohit Anand]

Assuming M is your matrix.

You can assign the splitted values to two different Matrices and then Plot them as needed.

MatA = M(:, 1:2) % All rows and first two columns assigned to MatA
MatB = M(:, 3:4) % All rows and the 3rd and 4th Column assigned to MatB

But There is no need to assign different variables to the splitted matrix. You can use M(:, 1:2) directly in your plot functions. This will keep the workspace clean.

[k]

I will try this, thank you. Is there a way to make this into a for loop so that the program executes this for any number of columns?

[Rohit Anand]

Yeah, Easily.

You want to split any number of columns in multiple matrices of two colums right?

You can do that,

Assuming M is the matrix

numCols = size(M, 2)
for i=1:2:numCols
    x = M(:, i:i+1); % x is the temp matrix
%     Do some operation on x like plot
end

This code will only work for Even Number of columns .But from the question I think that's exactly what numCols will be(even).

[k]

For some reason that only printed the last two columns but I found an alternative solution, thanks!

[Rohit Anand]

Can you post what you did? Cause the solution I suggested works just fine for me.

Answer 3

[Rohit Anand]

For Splitting a matrix in a loop You can use the colon operator.

M(:, 3:4) % Select 3rd and 4th column of M and all rows

M(3:4, :) % 3rd and 4th row of M and all columns.

If you want to split any number of columns in multiple matrices of two colums, You can use a for loop to do so.

M = randi(27, 6, 24)

numCols = size(M, 2);
for i=1:2:numCols
    x = M(:, i:i+1); % x is the temp matrix
    disp(x);
end

This code snippet should solve your problem.