Graph with stored data

Hi everybody,
I'm pretty new to NodeRed. I have a problem with making graph with data stored. My data are in Json format like :{"t":"2018-12-12T15:00:00.000Z","temp_in_cooling":"320.00"}. i Can make graph using directly these data by means of $.feeds.{"x":t, "y" :temp_in_cooling} with the exchange node. In this way i get an array of object (objects are x and y}. The problem is that i have so many others data for each time stamp that i need to process before (i have to make some moltiplications and if statement, so with a for loop i convert, the data from string to numbers and i do my operations and finally i gat an array. but i can't display that array in a graph, i guess i'd have to convert that array in a array of object or something like that.

This what i get if i create an array of number for processing the data:

Can anybody help me please?
Thank you!

First thing is to explore the documentation Chart with stored data
Format of the data to be feed to chart must be done correctly. So investigate, try and ask when you cant understand something.

Ok, i know which format i should use, the point is that i do not understand how to convert the format i have to the one i have to have to feed the chart! I should switch from number array to 'object' array? Or? I've tried everything..

Show us what have you tried. Share the function or flow where you try to manage your data into correct format for chart.
Also, there is many discussions have been done about same topic. Have you searched and read them? Many of them have almost ready to use solutions

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