Did you simply want to plot that complex-valued function of a real variable, f(x), you can do that with stem3
x= -50:50;
y = zeros(size(x));
y(x<0) = -1i;
y(x>0) = 1i;
y(x==0) = 1;
stem3(x,real(y),imag(y))
xlabel('x'); ylabel('Re(f(x))'); zlabel('Imag(f(x))');
