How to create a matrix from given vectors

I have a vector A= [ 2 4 1 3 ]

How can you create a matrix which are the length of the vector values with ones. the rest zeros?

i.e I want

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

Regards

jason

[Azzi Abdelmalek]

it's not clear

[Jason]

sorry - my first value in A is 2. So I want my first column of B to have 2 two entities both ones. A(2)=4 so i want my second column of B to have 4 values of ones. A(3)=1 so my thrid column of B only has the one 1. Overall I need this to be a matrix. So wherever there is no 1s present I want zeros.

my vecotrs of A will be a lot larger than demonstrated here so an automated way to create teh ones in the correct place for each value will be great.

Still not sure if this will be clear enough. I'm a novice and don't know all the terms.

jason

Answer 1

[Andrei Bobrov]

C = zeros(max(A),numel(A));
C(A + (0:numel(A)-1)*size(C,1)) = 1;
B = flipud(cumsum(C(end:-1:1,:)));

[Jason]

exactly what I mean thanks.

[Jason]

This method "falls" over when some values of zero are in the A matrix? i.e. if A=[5 3 4 0 8] it actually effects the column before.

[Azzi Abdelmalek]

Then try my code

[Matt Fig]

This fixes Andrei's code for when A has a zero (a possibility that should have been mentioned in the original post!)

C = zeros(max(A),numel(A));
idx = A + (0:numel(A)-1)*size(C,1);
C(idx(A>0)) = 1;
C = flipud(cumsum(C(end:-1:1,:)));

[Andrei Bobrov]

Thanks Matt.

Answer 2

[Matt Fig]

Here is the obligatory one liner. It works whether or not A has a zero.

D = cumsum(ones(max(A),length(A))) <= A(ones(1,max(A)),:);

Or (slower but memory efficient):

D = bsxfun(@(x,y) x<=y,(1:max(A)).',A);

[Andrei Bobrov]

+1

Answer 3

[Azzi Abdelmalek]

A= [ 2 4 1 3 ];
n=length(A);
s=meshgrid(1:n);
out=cell2mat(arrayfun(@(x,y) y<=A(x),s,s','un',0))

[Jason]

Thanks Azzi and sorry about the confusion. This however produces 4 matrices where I only needed the one. thanks

[Azzi Abdelmalek]

there are no 4, just one: out

[Jason]

sorry yes, this works thanks :)

[Jason]

is there a way to have it as a 6 by 3 matrix rather than a 6 by 6 matrix?

[Azzi Abdelmalek]

just extract

out(:,1:3)