# How to make a moving graph in Javascript P5

I have struggled to make my a moving graph in P5. My idea is to make a graph by the length of an array. If the length of the array increases the graph will move up and if it increases it will do the opposite.

My code can be seen at this link, (p5.js Web Editor), where I have made a comment, where the graph is

1 Like

Hi @mohashah,

I am not sure to understand your question. Could you be a little bit more specific ?

• What kind of graph would you like to draw ? (bar graph, line graph, …)
• How would you like to draw it specifically ?

From looking at your code it seems you are trying to replicate the visualization from this Washington Post article about viral spread. Could it be that you want to represent the number of infected people as a line graph ?

If that is the case just need to have a function that maps that data to a specific height.
You could call this function at each time step and store the corresponding height in an array/list. You would then just have to iterate over the list and draw a line between each height value.

``````const W = 680, H = 200; // dimensions of canvas
const time = 400; // number of x tick values
const step = W/time; // time step

let data = []; // to store number of infected people
let count = 0; // steps counter
let pos, fy, c, infected, colors, l, f;

function setup() {
createCanvas(W, H);
fill(255, 30, 70, 90);

// array containing the x positions of the line graph, scaled to fit the canvas
posx = Float32Array.from({ length: time }, (_, i) => map(i, 0, time, 0, W));

// function to map the number of infected people to a specific height (here the height of the canvas)
fy = _ => map(_, 3, 0, H, 10);

// colors based on height stored in an array list.
colors = d3.range(H).map(i => d3.interpolateWarm(norm(i, 0, H)))

}

function draw() {
background('#fff');

// length of data list -1 (to access last item of data list)
l = data.length -1 ;

// frameCount
f = frameCount;

// number of infected people (noised gaussian curved)
c = sin(f*0.008);
infected = (exp(-c*c/2.0) / sqrt(TWO_PI) / 0.2)  + map(noise(f*0.02), 0, 1, -1, 1);

// store that number at each step (the x-axis tick values)
if (f&step) {
data.push(infected);
count += 1;
}

// iterate over data list to rebuild curve at each frame
for (let i = 0; i < l; i++) {

y1 = fy(data[i]);
y2 = fy(data[i+1]);
x1 = posx[i];
x2 = posx[i+1];

// vertical lines (x-values)
strokeWeight(0.2);
line(x1, H, x1, y1 + 2);

// polyline
strokeWeight(2);
stroke(colors[Math.floor(map(y1, H, 10, H, 0))] );
line(x1, y1, x2, y2);

}

// draw ellispe at last data point
if (count > 1) {
ellipse(posx[l], fy(data[l]), 4, 4);
}

// reset data and count
if (count%time===0) {
data = [];
count = 0;
}

}
``````
3 Likes

hey @solub

Thank you for the detailed explanation, I appreciate it. It was exactly that type of graph I was looking for. Sorry i didn’t gave a more specific definition of my question.