Stacking multiple arrays into a matrix

How can i form a matrix out of n number of different column matrices of same size by placing them side by side.

Answer 1

[Dave B]

You can make append two columns like this:

a=rand(10,1);
b=rand(10,1);
c=[a b];
size(c)

ans = 1×2

10 2

or like this:

c=cat(2,a,b);
size(c)

ans = 1×2

10 2

Both approaches extend to n columns:

a=rand(10,1);
b=rand(10,1);
c=rand(10,1);
d=rand(10,1);
M1=[a b c d];
size(M1)

ans = 1×2

10 4

M2=cat(2,a,b,c,d);
size(M2)

ans = 1×2

10 4

Alternatively, you could initialize a matrix and then fill it with the columns:

M3=nan(numel(a),4); % you don't really need to initialize, but it is wise
M3(:,1) = a;
M3(:,2) = b;
M3(:,3) = c;
M3(:,4) = d;
size(M3)

ans = 1×2

10 4

[HEMRAJ PATEL]

Can you please explain it using for loop as i have n no. of column matrices. My n extends to 2000.

[Image Analyst]

@HEMRAJ PATEL surely they don't all have unique names though. You don't have 2000 separately named individual variables do you, because that would be a disaster.

[HEMRAJ PATEL]

In case of

c=cat(2,a,b);

size(c);

if i have 2000 matrices like (c1,c2,c3,...,c2000) and i want them in cat function.

How will i do it.

Do i have to write c=cat(2,c1,c2,c3....) or do we have another option

[Dave B]

Where do c1, c2, etc come from? Can you create them as a matrix to begin with? How are they identified? is it all variables in the workspace that begin with the letter c?

In theory, you could create a statement like the one above using eval...but as @Image Analyst if you have 2000 separately named variables that sounds like a disaster, and if you're using the variable name to indicate column identity that's probably also not great.

[Stephen23]

"if i have 2000 matrices like (c1,c2,c3,...,c2000) and i want them in cat function. How will i do it."

I have some ideas of how you might do it, but no experienced MATLAB users would do that.

"Do i have to write c=cat(2,c1,c2,c3....) or do we have another option"

Another option is better data design: don't have numbered variable names.

Numbered variable names is a sign that you are doing something wrong. Use indexing instead.

[HEMRAJ PATEL]

Thanks for your valuable replies. I have solved my problem, i might have framed my question wrong.