How to insert an unknown number of coloumn in a Matrix?

Hi everybody,

I'd like to add a number of coloumns specified in a variable to a matrix in certain positions.

The coloumns will be represented by arrays of just one value, the positions should divide equally (when possible) the matrix.

I'll make an exemple:

>> A=reshape(1:16,4,4)
A =
       1     5     9    13
       2     6    10    14
       3     7    11    15
       4     8    12    16
>> B(1,1:4)=-1;
>>B=B';

After modification I'll have:

For 3 coloumns to be inserted

NumCol=3;
A=       
       1    -1    5    -1     9    -1    13
       2    -1    6    -1    10    -1    14
       3    -1    7    -1    11    -1    15
       4    -1    8    -1    12    -1    16

For just one

NumCol=1;
A=       
       1    5    -1     9    13
       2    6    -1    10    14
       3    7    -1    11    15
       4    8    -1    12    16

I can find my self the way to understand where to insert coloumns. My problem is how??

Can somebody help me please?

Answer 1

[madhan ravi]

Try this:

B=rand(3); % your initial matrix
[m,n]=size(B);
No_of_Columns=input('No of columns to be inserted')
disp('No of columns and NUMEL(where) should be equal')
where=input('inserting position_s')
Wanted=zeros(m,n+ncs)
A_constant=input('A scalar Value to be assigned')
Wanted(:,where)=A_constant
Wanted(:,setdiff(1:size(Wanted,2),where))=B

[Giuseppe Sarda]

Works as I wanted! Thanks!

Answer 2

[Guillaume]

It's hard to tell you a generic way without understanding how the insertion points are chosen.

In your first case, I would do:

newA = repmat(B, 1, size(A, 1) + NumCol);  %fill with B
newA(:, 1:3:end) = A  %copy A in odd columns

In your second case, I would do:

newA = [A(:, 1:2), B, A(:, 3:end)]

[Giuseppe Sarda]

I will choose insertion points in order to divide equally sectors on the matrix (where possible).

A possible solution can be inserting the vector every colsOnSector:

colsOnSectors=round(totalNumCols/numColsToBeinserted);

I hope it's clear enough!

[Guillaume]

This is how I'd do it then:

%A: a matrix of any size
%B: a column vector (or matrix) of the same height as A, to be inserted at regular interval in A
%NumCol: the number of times B must be inserted

splitdist = round(linspace(0, size(A, 2), NumCol + 2)); %find how to split A
newA = cell(1, 2*numel(splitdist) - 3);
newA(1:2:end) = mat2cell(A, size(A, 1), diff(splitdist));  %split and distribute A
newA(2:2:end) = {B};  %distribute B
newA = cell2mat(newA)