array to matrix transformation with size[ length of array , largest element in array]

I have an array [1 1 2 3 1 2 1 ] I want to generate a matrix of size [7x3] as length of array is 7 and maximum element is 3. for example the output look like this

A=[1 0 0
   1 0 0
   0 1 0
   0 0 1
   1 0 0
   0 1 0
   1 0 0]

showing that the 1st element of array assigns 1 to the corresponding column in A. for example the 1st element is 1 so row 1 and column 1 gets value 1, the 3rd element is 2 so row 3 column 2 gets value 1 and so on. Is there any way to do so? I tried diag[array] but it gives a 7x7 matrix

Answer 1

[Stephen23]

No need to for any ugly loops, just use sub2ind:

>> C = [1,1,2,3,1,2,1];
>> R = 1:numel(C);
>> Z = zeros(R(end),max(C));
>> Z(sub2ind(size(Z),R,C)) = 1
Z =
     1     0     0
     1     0     0
     0     1     0
     0     0     1
     1     0     0
     0     1     0
     1     0     0

[summyia qamar]

thankyou.God bless you

Answer 2

[Image Analyst]

Did you try the obvious brute force way:

array = [1 1 2 3 1 2 1 ]
lengthA = length(array)
maxA = max(array)
A = zeros(lengthA, maxA)
for k = 1 : lengthA
  A(k, array(k)) = 1;
end
A % Report to the command window

[summyia qamar]

thankyou for your help

Answer 3

[Steven Lord]

If you want this to be a full array, use accumarray. If the number of rows and/or columns is expected to be large consider using sparse.

% Full
cols = [1 1 2 3 1 2 1 ];
cols = cols(:);
rows = (1:length(cols)).';
A = accumarray([rows, cols], 1)

% Sparse
cols = [1 1 2 3 1 2 1 ];
S = sparse(1:length(cols), cols, 1)
isequal(A, full(S))

[summyia qamar]

thankyou for you concern