Working with Data in Highcharts for Python

The Highcharts for Python Toolkit is a data visualization library. That means that it is designed to let you visualize the data that you or your users are analyzing, rather than to do the analysis itself. But while there are better tools to actually crunch the numbers, Highcharts for Python still has to work closely with your data in order to visualize it.

When working with Highcharts for Python, it can be useful to understand:

  1. How Highcharts for Python represents your data

  2. How to load your data into a Highcharts for Python object

  3. How to adjust your data in Highcharts for Python

  4. How Highcharts for Python serializes your data for Highcharts (JS).

Highcharts for Python Data Model

In broad brushstrokes, you can think of your Highcharts for Python chart as a tree.

At the root of the tree is a Chart, and that chart contains options (HighchartsOptions). Those options in turn contain a collection of series, each of which can be thought of as one “line” of data in your visualization.

Each series instance (descended from SeriesBase) contains a .data property, which contains a set of data points.

Depending on your data and your configuration, this set of data points may be represented as:

  • a DataPointCollection instance (or a descendent of it) which in turn contains your data values and related configuration options

  • an iterable of DataBase-descended instances, each of which contains the data value and configuration of an invidual data point

This model is relatively straightforward, but there is one important complexity: the relationship between DataPointCollection instances and DataBase instances.

DataPointCollection vs DataBase

The DataPointCollection class stores your individual data points in a combination of three different list-like structures:

  • as a numpy.ndarray in the .ndarray property

  • as a list of DataBase instances in the .data_points property

  • as a list of primitives (e.g. numbers, strings, etc.) in the .array property

Why split it up like this? The purpose is to maximize performance within both Highcharts for Python and Highcharts (JS), while still minimizing outside dependencies.

Highcharts (JS) supports data organized in primitive arrays. So it can easily visualize something like the following:

[
    [0, 12],
    [1, 34],
    [2, 56],
    [3, 78],
    [4, 90]
]

This way of representing your data gives you the fastest performance in Highcharts (JS), leading to lightening-fast rendering of your chart. And since it’s just a simple list of numbers, Highcharts for Python doesn’t have to apply any fancy logic to serialize it to JS literal notation - leading to fast performance in Python as well.

This is why the DataPointCollection separates the data that can be represented as a primitive array (stored in either .ndarray or .array), from data point properties that need to be represented as a full Highcharts (JS) data point object (stored in .data_points).

And if you’re familiar with NumPy, that looks just like a ndarray - and for good reason! If you have NumPy <https://www.numpy.org> installed, Highcharts for Python will leave your ndarray objects as-is to benefit from its vectorization and performance.

Internally, DataPointCollection instances will intelligently combine the information stored in these three different properties to serialize your data points. This is done as-appropriately, generating a list of renderable data points represented either as a primitive array, or as full objects, depending on the properties that have been configured.

So do you have to worry to about this complexity? Not really! All of this happens under the hood in the Highcharts for Python code. You can simply load your data using the convenience methods available on your series instances DataPointCollection or its descendents, or simply pass your data to the series .data property.

Let’s see how this works in practice.

Loading Data into Highcharts for Python

Preparing Your Data

So let’s try a real-world example. Let’s say you’ve got some annual population counts stored in a CSV file named 'census-time-series.csv'. There are four different ways you can represent this data:

  1. As-is in the CSV file. Meaning you don’t do anything, just leave it in the file as-is.

  2. Loaded into a Python iterable (i.e. a list of list, where each inner list represents a row from the CSV). This might look something like this:

    raw_data = [
    ['United States', 309321666, 311556874, 313830990, 315993715, 318301008, 320635163, 322941311, 324985539, 326687501, 328239523],
    ['Northeast',  55380134, 55604223, 55775216, 55901806, 56006011, 56034684, 56042330, 56059240, 56046620, 55982803],
    ['Midwest', 66974416, 67157800, 67336743, 67560379, 67745167, 67860583, 67987540, 68126781, 68236628, 68329004],
    ...
]

  3. As a numpy.ndarray, which might look like this:

  4. As a pandas.DataFrame, which might look like this:

Now that we’ve got our data prepared, let’s add it to a series or chart.

Creating a Series/Chart with Data

Note

In this tutorial, we’ll focus on assembling one or more series of data, rather than a complete chart. This is because chart’s have many more configuration options, but fundamentally the data that they contain is stored within one or more series instances, which themselves contain data points in a DataPointCollection or an iterable of DataBase instances.

So now that we have raw_data prepared, we can now load it into a series. There are four ways to do this:

  1. By passing it to the .data property of our series when instantiating the series:

    from highcharts_core.options.series.area import LineSeries

my_series = LineSeries(data = raw_data)

  2. By calling one of the “helper” methods:

from highcharts_core.options.series.area import LineSeries

# If my data is either a numpy.ndarray or Python iterable
my_series = LineSeries.from_array(raw_data)

# If my data is in a Pandas DataFrame
my_series = LineSeries.from_pandas(raw_data)

# If my data is in a CSV file
my_series = LineSeries.from_csv('census-time-series.csv')

See also

Depending on the arguments you supply to the helper methods, they may produce multiple series for inclusion on your chart. For more information, please see:

  1. By instantiating your set of data directly, and passing it to the .data property of our series:

    from highcharts_core.options.series.area import LineSeries
from highcharts_core.options.series.data.cartesian import CartesianData

my_data = CartesianData.from_array(raw_data)

my_series = LineSeries(data = my_data)

    Depending on the arguments you supply to the helper methods, they may produce multiple series for inclusion on your chart. For more information, please see:

  1. By instantiating individual data points directly, and passing it to the .data property of our series:

    from highcharts_core.options.series.area import LineSeries
from highcharts_core.options.series.data.cartesian import CartesianData

my_data = [CartesianData(x = record[0], y = record[1] for record in raw_data]

my_series = LineSeries(data = my_data)

In all cases, the result is the same: a LineSeries instance (or a list of LineSeries that contain your data.

Now that your data has been loaded into your series, you can configure it as needed.

Configuring Your Data

In most cases, you shouldn’t have to worry about the internals of how Highcharts for Python stores your data. Depending on whether you supplied a primitive array, a numpy.ndarray, or data from a Pandas DataFrame, your series’ data will either be represented as a DataPointCollection or as a list of data point objects (descended from DataBase).

In all cases, you can easily set properties on your data via your series object itself. For example, let’s say we wanted to configure the .target values on data points in a BulletSeries instance. We can do that easily by working at the series level:

# EXAMPLE 1.
# Supplying one value per data point.

my_series.target = [1, 2, 3, 4, 5, 6]

# EXAMPLE 2.
# Supplying one value, which will be applied to ALL data points.

my_series.target = 2

This propagation of data point properties extends to all data point properties. If a property of the same name exists on the series, it will be set on the series. But if it only exists on the data point, it will be propagated to the relevant data points.

In some circumstances, you may want to set data point properties that have identically-named properties on the series. For example, data points and series both support the .id property. But you can set this property at the data point level in two ways:

  1. If your data point is represented as a DataPointCollection, you can simply set it as a sub-property of the series .data property:

    # EXAMPLE 1.
# Supplying one value per data point.
my_series.data.id = ['id1', 'id2', 'id3', 'id4', 'id5', 'id6']

# EXAMPLE 2.
# Supplying one value, which will be applied to ALL data points.

my_series.data.id = 'id2'

The DataPointCollection will worry about proagating the relevant property / value to the individual data points as needed.

  1. If you data points are represented as a list of DataBase-descended objects, then you can adjust them the same way you would adjust any member of a list:

    id_list = ['id1', 'id2', 'id3', 'id4', 'id5', 'id6']
for index in range(len(series.data)):
    series.data[index].id = id_list[index]

In this case, you are adjusting the data points directly, so you do need to make sure you are adjusting the exact properties you need to adjust in the exact right location.

Updating Your Data

You can also update your data after it has been loaded into your series. This is done by calling one of the .load_from_* series helper methods, which makes it possible to update your series’ data just like when creating the series:

# EXAMPLE 1.
# Updating the .data property

my_series.data = updated_data

# EXAMPLE 2.
# If my data is either a numpy.ndarray or Python iterable

my_series.load_from_array(updated_data)

# EXAMPLE 3.
# If my data is in a Pandas DataFrame

my_series.load_from_pandas(updated_data)

# EXAMPLE 4.
# If my data is in a CSV file

my_series.load_from_csv('updated-data.csv')

Serializing Your Data for Rendering

While you shouldn’t have to serialize your data directly using Highcharts for Python, it may be useful to understand how this process works.

First, it’s important to understand that Highcharts (JS) supports data represented in two different forms:

JS literal objects are the most flexible, because they allow you to take advantage of all of the different data point configuration options supported by Highcharts. However, primitive arrays perform much faster: Highcharts for Python generates them faster, there’s less data to transfer on the wire, and Highcharts (JS) can render them faster.

For this reason, Highcharts for Python will always try to serialize your data points to a primitive array first. If the series type supports a primitive array, and there is no information configured on the data points that prevents it from being serialized as a primitive array, Highcharts for Python will default to that form of serialization.

However, if there are special properties (not supported by primitive arrays) set on the data points, or if the series type is one that does not support primitive arrays, then Highcharts for Python will generate a JavaScript literal object instead.

This logic all happens automatically whenever you call .to_js_literal() on your series.