Reshaping (M,N)-matrix to (M,1)-matrix

Hello everyone,

I have a matrix, for example:

A = [1, 2, 3;

   4, 5, 6;

   7, 8, 9]

and now I want to create a matrix:

A = [123;

   456; 

   789]

Does anybody know how I can do this efficiently?

(I need to do this 62.000 times for my matrix)

Answer 1

[Andrei Bobrov]

z = floor(log10(A)+1);
z(isinf(z)) = 1;
ex = fliplr(cumsum([zeros(size(A,1),1), fliplr(z(:,2:end))],2));
out = sum(A.*10.^ex,2);

eg:

> A =[14 10 3    16
  12  0  10   18
  3   11 14   7
  9   13 0   20];

> z = floor(log10(A)+1);
> z(isinf(z)) = 1;
> ex = fliplr(cumsum([zeros(size(A,1),1), fliplr(z(:,2:end))],2));
> out = sum(A.*10.^ex,2)

out =
       1410316
       1201018
        311147
        913020

[Jonathan]

Thanks! Works like a charm and fast as well!

[Jonathan]

Only one small problem with this:

It adds zeroes to the end of my numbers and I would like that not to happen since my numbers are timestamps. Do you know how I can stop Matlab from adding those extra zeroes?

Thanks in advance!

[Andrei Bobrov]

I corrected.

Answer 2

[Jos (10584)]

Another trick using strings:

    A = [1 2 3 ; 10 11 12 ; 90 0 99]
    B = str2num(sprintf([repmat('%d',1,size(A,2)) ' '],A.')).'

[Andrei Bobrov]

+1

[Jos (10584)]

Note that you can play around with the "%d". For instance, you can use "%02d" so that a single digit number will be have a leading zero.

Answer 3

[Simon]

Hi!

So your resulting matrix is a vector. right?

Try this

   mat10 = ones(size(A, 1), 1) * 10.^((size(A, 2)-1):-1:0);
   sum(A .* mat10, 2)

This is applicable for matrices of any size.

In string form

str2num(char(regexprep(cellstr(num2str(A)), ' ', '')))