generate a matrix with numbers between [0,1]

I have to generate a matrix of n x n uniformly distributed random numbers (n read from keyboard). The numbers should be between [0,1] and then to average the numbers > 0.5. I've tried the following:

value = 'Insert a value for n: ';
x = input(value);

matrix = rand(x,x);

matrix2(matrix < 0.5) = nan;

average = mean(matrix2, 'omitnan');
disp(average);

After I run the code I get that average is 0 and I don't know why.

Answer 1

[KSSV]

value = 'Insert a value for n: ';
x = input(value);
matrix = rand(x,x);
matrix2 = matrix ;   % you need to create matrix2 
matrix2(matrix < 0.5) = nan;

average = mean(matrix2, 'omitnan');
disp(average)