How to select an array without element i

I want to select an array of a matrix without element i

so if

a =

       1     
       4     
       7    
      11    

n = 4
V = zeros(3,n)

i want to be able to select

   a(:-i)

pseudo code:

for i = 1:n
    V(:,1) = a(:-i) %so everthing from a except from element on i'th place
end

And then I want the output to be

V =

     4     1     1     1
     7     7     4     4
    11    11    11     7

I hope someone can help me! sorry for bad englisch

[Stephen Cobeldick]

Question for those who enjoy challenges: is there a solution which does not remove elements from a larger array? That would mean no setdiff, eye, etc, and extra points if it does not use a loop :)

Answer 1

[Stephen Cobeldick]

>> a = [1;4;7;11];
>> n = numel(a);
>> M = reshape(a(1+mod(setdiff(1:n*n,1:n+1:n*n)-1,n)),n-1,n)
M =
    4    1    1    1
    7    7    4    4
   11   11   11    7

Answer 2

[H ZETT M]

This is not pretty, but it works:

a =[1;4;7;11] 

n = 4
V = zeros(3,n)

    for i=1:n    
    V(:,i)=a([1:i-1 i+1:end])';
    end

Answer 3

[Jan]

While I prefer Stephen's or Andrei's vectorized solutions for the productive use, the actual question can be solved in a loop also:

a = [1; 4; 7; 11];
n = 4;
V = zeros(3, n);
for k = 1:n
  V(:, k) = a(setdiff(1:n, k));
end

Or:

index = true(1, 4);
for k = 1:n
  index(k) = false;
  V(:, k)  = a(index);
  index(k) = true;
end

Or:

V = repmat(a, 1, n);
V(1:n+1:end) = [];
V = reshape(V, n-1, n);

Or:

[index, dummy] = find(~eye(n));
V = reshape(a(index), [], n)

[Andrei Bobrov]

+1

Answer 4

[Andrei Bobrov]

n = numel(a);
V = reshape(nonzeros(repmat(a,1,n).*~eye(n)),[],n)