Unexpected behaviour of Plotly.Update

plotly.js
1

Hi,
I have problem with update function (or maybe with my approach).
Here is my situation:

  • I use scatter line plot with many traces (xaxis - timestamps, yaxis - integer values)
  • by every 1 minute app ask API for new data {x: [timestamp1, timestamp2], y: [value1, value2]}
  • after that I would like to update xaxis domain (with timestamps) and put new data (timestamp1, value1) into the end of existing plot data array.

I found out that it’s possible to use Update function, but I have problem, that after update, my old trace data dissapear and I can see only new data.
https://codepen.io/anon/pen/rgPgxx - uncoment line: //Plotly.update(‘myDiv’, update, {}, [0]) and then you can see it.
I thought that update “add” new data to existing trace without cleaning old data. I don’t know if it’s normal behavoiur or it’s a bug?

And second question: I also use Plotly.extendTraces function (xaxis: timestamps, yaxis: INT_VALUES). I’m showing only 30 min latest data for user and update plot by every 5 minutes. Can you tell if I have to take care about old data (older than 30 min.) by myself and clean somehow traces or Plotly.extendTraces do it automaticly?

2

Plotly.update will replace the old data with the new arrays, so the behavior you’re describing is the expected one.

You should try using extendTraces, see example here: Function reference in JavaScript

I think setting the 4th extendTraces argument should do the trick here.

1 Like
3

Thanks for your response. I thought that Plotly.update add traces not replace. It’s not clear in documentation.

I’ll try with mix functions: Plotly.relayout and Plotly.extendTraces:slight_smile: