Processing large data from an API to visualise

Let's say I have an API that gives me the values of stock for the last month. The data is sampled every hour.

Now I want to make a web app that would visualize this data on a line chart. I don't need all the hourly samples, so my question is how should I make this work?

My idea is that there would be a backend app (i.e. in Java Spring) that would GET the data from the API and calculate the average for each day (using a stream, maybe parallel stream?) and then put that in a new collection and pass it on to the front end to put in a chart.