Histogram: draw the amount of samples in ranges of values#

A histogram is a visual representation of the distribution of quantitative data. In other words, it allows to represent the amount of samples for which a chosen attribute is contained in a range of values.

How to draw a Histogram ?#

  1. Import the required packages

# Required packages
import random
import plot_data as pld
from plot_data.colors import BLUE, GREEN

  1. Create data

In order to draw a Histogram of a variable sampled randomly, build a random vector of samples (stored as Python dict) with one attribute. Here we chose to build a vector of length sampled within a Gaussian distribution.

# Vector construction
elements = [{'length': random.gauss(0, 3)} for _ in range(500)]

  1. Set styles for bars and axes

Styles for bars and axes can be customized with the user’s preferences:

# Surface Style
surface_style = pld.SurfaceStyle(color_fill=BLUE)

# Edge Style
edge_style = pld.EdgeStyle(line_width=1, color_stroke=GREEN, dashline=[5, 3])

  1. Build the Histogram object and draw it in a web browser

When building the histogram, ticks number on x axis can be specified with the graduation_nb attribute.

histogram = pld.Histogram(x_variable='length',
                          elements=elements,
                          graduation_nb=20,
                          surface_style=surface_style,
                          edge_style=edge_style)

Once done, the figure can be displayed with the following command line:

pld.plot_canvas(plot_data_object=histogram, canvas_id='my_histogram')

Histogram Features#

  • Rubberbands can be drawn on axes by clicking and dragging on it with mouse. Rubberbands allow to select range of values on each axis,

  • Bars tooltips give information on how samples are distributed within a clicked bar,

  • The view can be adjusted with mouse interactions (click, drag and wheel),

  • One can select several bars with several mouse click by keeping pressed Ctrl key,

  • One can reset the view by pressing Ctrl + Space,

  • One can reset the whole figure by pressing Ctrl + Shift + Left Click.

How to write a method to draw a Histogram in a DessiaObject ?#

For the previously designed PendulumDOE ([section 2.2.2](https://www.notion.so/Using-data-display-with-PlotData-30f86e58db6240788cf4f3b543b0ae51?pvs=21)), an interesting plot may be to draw the distribution of pendulums speeds within the previously designed PendulumDOE class.

To do it, add a method to draw a Histogram to the PendulumDOE class:

class PendulumDOE(Dataset):
    :
    :
    :
  @plot_data_view("histogram")
  def histogram(self, reference_path: str = "#"):
    elements = [{"speed": pendulum.max_speed} for pendulum in self.dessia_objects]
    return pld.Histogram(x_variable="speed", elements=elements, graduation_nb=20)

And draw the Histogram with the function plot_canvas:

# Parameters sampling definition
planet_sampling = BoundedAttributeValue('g', 1, 11, 10)
length_sampling = BoundedAttributeValue('length', 0.1, 3, 10)

# DOE instantiation
pendulum_doe = PendulumDOE.from_boundaries(planet_sampling, length_sampling, 10, 0.01, method = 'fullfact')

# Parallel Plot construction
histogram = pendulum_doe.histogram()

# Draw the figure in a web browser
pld.plot_canvas(plot_data_object=histogram, filepath="section_2_5_2_histogram")