Dataset is a simple wrapper around a datasource for plotting charts.

Dataset marshalls a couple of different data structures into a consistent form for consumption by the chart plotting functions. For example, it allows a list of lists or a list of tuples to be treated the same.

The most sensible way to work with a dataset is to provide column headers - it makes code elsewhere readable. If you don't want to, you can also refer to columns by index.

Dataset provides a few convenience functions for calculating data extents for a column, extracting unique values from columns, calculating combined extents for multiple columns (handy when plotting bar charts) and guessing column type (handy when determining whether to use a Contex.TimeScale or a Contex.ContinuousLinearScale).

The easiest pattern to create a dataset is:

iex> data = [
...>        {0.0, 0.0, "Hippo"},
...>        {0.5, 0.3, "Turtle"},
...>        {0.4, 0.3, "Turtle"},
...>        {0.2, 0.3, "Rabbit"}
...>        ] # Wherever your data comes from (e.g. could be straight from Ecto)
...> dataset = Dataset.new(data, ["x", "y", "category"]) # Attach descriptive headers
...> Dataset.column_extents(dataset, "x") # Get extents for a named column
{0.0, 0.5}
iex> Dataset.column_name(dataset, 0) # Get name of column by index
"x"
iex> cat_col = Dataset.column_index(dataset, "category") # Get index of column by name
2
iex> Enum.map(dataset.data, fn row -> # Enumerate values in a column
...>    Dataset.value(row, cat_col)
...> end)
["Hippo", "Turtle", "Turtle", "Rabbit"]
iex> Dataset.unique_values(dataset, "category") # Extract unique values for legends etc.
["Hippo", "Turtle", "Rabbit"]

While Dataset gives facilities to map between names and column indexes, you can only access data values via index. This is so that you don't have expensive mappings in tight loops.

Note There are very few validation checks (for example, to checks that number of headers supplied matches) the size of each array or tuple in the data. If there are any issues finding a value, nil is returned.