Data used as sources for visualizations is usually organized in some kind of structure. The most common structures are probably lists (arrays) and tables (maps), stored in some standard data format. When using data from external sources, you usually need to clean it up, removing unnecessary values, simplifying its structure, applying bounds, and so on. After that, you can parse it and finally store it locally in a JavaScript array or JavaScript object that can be used by the chart.

Once your data is stored in a JavaScript data structure, you can transform it further by applying mathematical operations on the stored values. You can change the structure, create new fields, merge, and delete data. Typical operations include pushing new values into the dataset, splicing or splitting the array, creating a subset, transforming data, and so on. JavaScript provides many native operations that make it easier to modify arrays and objects. You can also use libraries such as JQuery.