File:DiscreteGraph.svg

outputformat := "svg";

beginfig(1);
u := 1cm;

% Axes
drawarrow (0,0) -- (0,5u);
for i=1 upto 4: label.lft(decimal i,(0,i*u)); endfor
label.rt("f", (0,5u));
drawarrow (0,0) -- (6u,0);
for i=1 upto 5: label.bot(decimal i,(i*u,0)); endfor
label.top("i", (6u,0));

% A macro to draw a vertical line at x-coordinate n and of height h.
def draw_with_points (expr n, h) =
    begingroup
        pickup defaultpen;
        draw (n*u,0) -- (n*u,h*u);
        pickup pencircle scaled 4pt;
        for i=1 upto h:
            drawdot (n*u,i*u);
        endfor
    endgroup
enddef;

% The graph.
draw_with_points(1,3);
draw_with_points(2,1);
draw_with_points(3,3);
draw_with_points(4,4);
draw_with_points(5,3);

% The horizontal lines
pickup defaultpen;
for i=1 upto 4:
    draw (0,i*u) -- (6u,i*u) dashed evenly;
endfor
endfig;