secomind / ex_lttb

An Elixir downsampling library that retains the visual characteristics of your data

ExLTTB

An Elixir downsampling library that retains the visual characteristics of your data.

ExLTTB is based on Largest-Triangle-Three-Buckets (LTTB) and it contains two implementation modules: ExLTTB implements the original algorithm using Enum and eager evaluation, ExLTTB.Stream implements a slightly modified version to cope with lazy evaluation and using Stream.

The data is assumed to be ordered by its x coordinate in both implementations.

Installation

Add ex_lttb to your list of dependencies in mix.exs:

def deps do
  [
    {:ex_lttb, "~> 0.3.0"}
  ]
end

Documentation

You can read the documentation on HexDocs.

Examples

# Downsample a list of data in the default shape of %{x: x, y: y}
input_samples = for x <- 1..100, do: %{x: x, y: :random.uniform() * 100}

# 30 output samples
output_samples = ExLTTB.downsample_to(input_samples, 30)

# Downsample a list of data of arbitrary shape
input_samples =
  for x <- 1..100 do
    %{nested: %{timebase: x},
      data: :random.uniform() * 100,
      untouched_other_key: :random.uniform() * 3
    }
  end

sample_to_x_fun = fn sample -> sample[:nested][:timebase] end
sample_to_y_fun = fn sample -> sample[:data] end
xy_to_sample_fun = fn x, y -> %{nested: %{timebase: x}, data: y} end

output_samples =
  ExLTTB.downsample_to(
    input_samples,
    30,
    sample_to_x_fun: sample_to_x_fun,
    sample_to_y_fun: sample_to_y_fun,
    xy_to_sample_fun: xy_to_sample_fun
  )

# Downsample a stream of data
input_stream =
  Stream.iterate(%{x: 0, y: :random.uniform() * 100}, fn %{x: x} -> %{x: x + 1, y: :random.uniform() * 100} end)

# Downsample rate of 2.3
output_samples = ExLTTB.Stream.downsample(input_stream, 2.3) |> Enum.take(20)

# The options for arbitrary shaped data are the same for the streaming version