How to map a value of a vector into column number of a matrix?

let A=[2;4;5] vector I want a matrix where all the values will be zero and the 2nd 4th and 5th element of column of 10x3 matrix will be 1.

B=[0 0 0
   1 0 0
   0 0 0
   0 1 0
   0 0 1
   0 0 0
   0 0 0
   0 0 0
   0 0 0
   0 0 0 ]

Answer 1

[Jan]

A = [2, 4, 5];

B      = zeros(10, 3);
idx    = sub2ind(size(B), A, 1:3);
B(idx) = 1;

[Mushahid Shamim]

How to take 1:3 from a function output. I tried 1:end but doesn't work

[Jan]

idx = sub2ind(size(B), A, 1:size(B, 2));

The end command must appear as an index of an array. Otherwise Matlab could not know, which ending you mean.

[Jos (10584)]

this seems to be a new question ...

[Jan]

@Jos: I assume, Mushahid means the "1:3" from "sub2ind(size(B), A, 1:3)".

Answer 2

[Andrei Bobrov]

n = numel(A);
B = accumarray([A(:),(1:n)'],1,[10,n]);

Answer 3

[Jos (10584)]

A fast and easy one-liner from the old days, when accumarray did not exist :)

A = [2 ; 4 ; 5]
B = full(sparse(A, 1:numel(A), 1, 10, 3))