Matplotlib - Bar Chart - Part One

   
   
 python  
 visual  
Python Visualization Article Series

This is a multiple-parts article. There are few sections here.

Table of Content
Where to Discuss?

Local Group

Preface

Goal: Prepare data structure for plot a bar chart.

Prepare

Do not Rush! As mentioned in previous article.

The issue with barchart is preparing data structure, that can be read by human easy. We will have matrix as the data structure, and tranpose the matrix later using numpy.

The other stuff has been explained in matplotlib official stuff.

Preview

The final result would be as below:

Matplotlib: Cumulative Bar Chart: Vertical Plot

1: Data Structure

Consider data structure as a starting point.

We are going to use dog breeds as our data structure.

Simple Example

To represent dog’s age we can use array, in which represent:

  1. Puppy
  2. Junior
  3. Adult
  4. Senior
  stages = [3,  2,  3,  4]

Script

For multiple breed, we can utilize dictionary. The python script is simple:

population = {
  "Labradors"   : [ 10,  0,  0,  0],
  "Bulldogs"    : [ 10,  0,  0,  0],
  "Shepherd"    : [  4, 14,  0,  0],
  "Retrievers"  : [  2, 10,  3,  1],
  "Poodles"     : [  4,  8, 12,  0],
  "Beagles"     : [  0,  0, 10,  0],
  "Rottweilers" : [  0,  0, 10,  0],
  "Pointers"    : [  1,  0,  9,  0],
  "Dachshunds"  : [  0,  0,  9,  0],
  "Terriers"    : [  3,  0,  7,  0],
  "Boxers"      : [  0,  2,  4, 10],
  "Huskies"     : [  0,  0,  1,  0],
  "Spaniels"    : [  2,  1,  0,  0],
  "Doberman"    : [  9,  0,  0,  0],
}

ViM: Python: Data Structure

It is easier to represent the data this way.

Extracting Data

To get each breed names and each stages, are just getting the key-value for each dictionary.

import numpy as np

population = {
  "Labradors"   : [ 10,  0,  0,  0],
  ...
}

breeds    = list(population.keys())
stages    = list(population.values())

Tranpose

The stages is a two dimensional array. We can easily transpose the matix using numpy.

breeds    = list(population.keys())
stages    = list(population.values())
transpose = np.array(stages).T

Statistic

Seems like basic statistic right? But no. We haven’t get there yet.

This article only discus the vizualization stuff.

2: Using Population Data

Test the data in CLI, before jump into chart.

Pretty Print

Since in real world we have to deal with a lot of data. It is wise to setup pretty print. So we can read and then examine the result easily, without hurting your good retina.

Breeds

Consider begin with breed names.

import pprint
from MyPopulation import breeds, stages, transpose

my_print = pprint.PrettyPrinter(
  width=54, compact=True)
my_print.pprint(breeds)

Run the script above. This will show you this below:

❯ python 01-matrix-a.py
['Labradors', 'Bulldogs', 'Shepherd', 'Retrievers',
 'Poodles', 'Beagles', 'Rottweilers', 'Pointers',
 'Dachshunds', 'Terriers', 'Boxers', 'Huskies', 'Spaniels',
 'Doberman']

ViM: Python: Pretty Print: Breeds

Stages

Then continue with stages. We will get matrix.

import pprint
from MyPopulation import breeds, stages, transpose

my_print = pprint.PrettyPrinter(
  width=54, compact=True)
my_print.pprint(stages)

Run the script above. You will get this two dimensional array with pretty print.

❯ python 01-matrix-b.py
[[10, 0, 0, 0], [10, 0, 0, 0], [4, 14, 0, 0],
 [2, 10, 3, 1], [4, 8, 12, 0], [0, 0, 10, 0],
 [0, 0, 10, 0], [1, 0, 9, 0], [0, 0, 9, 0],
 [3, 0, 7, 0], [0, 2, 4, 10], [0, 0, 1, 0],
 [2, 1, 0, 0], [9, 0, 0, 0]]

ViM: Python: Pretty Print: Stages

Transposed Stages

And also the transposed matrix of the dog breeds population.

stages    = list(population.values())
transpose = np.array(stages).T
from pprint import pprint
from MyPopulation import breeds, stages, transpose

pprint(transpose)

Run the script above. You will get this two dimensional array with pretty print.

❯ python 01-matrix-c.py
array([[10, 10,  4,  2,  4,  0,  0,  1,  0,  3,  0,  0,  2,  9],
       [ 0,  0, 14, 10,  8,  0,  0,  0,  0,  0,  2,  0,  1,  0],
       [ 0,  0,  0,  3, 12, 10, 10,  9,  9,  7,  4,  1,  0,  0],
       [ 0,  0,  0,  1,  0,  0,  0,  0,  0,  0, 10,  0,  0,  0]])

ViM: Python: Pretty Print: Transposed Stages

3: Getting Each Stages

We are almost done. Now we can have each stages of dog breed population.

Extracting Stages

Just get the stages by array index.

from pprint import pprint
from MyPopulation import breeds, stages, transpose

puppy  = transpose[0]
junior = transpose[1]
adult  = transpose[2]
mature = transpose[3]

pprint(puppy)
pprint(junior)
pprint(adult)
pprint(mature)

Run the script above. You will get these one dimensional array of each four stage.

❯ python 01-matrix-d.py
array([10, 10,  4,  2,  4,  0,  0,  1,  0,  3,  0,  0,  2,  9])
array([ 0,  0, 14, 10,  8,  0,  0,  0,  0,  0,  2,  0,  1,  0])
array([ 0,  0,  0,  3, 12, 10, 10,  9,  9,  7,  4,  1,  0,  0])
array([ 0,  0,  0,  1,  0,  0,  0,  0,  0,  0, 10,  0,  0,  0])

Desrtructuring Stages

It is easier to extract using destructuring syntax.

from pprint import pprint
from MyPopulation import breeds, stages, transpose

[puppy, junior, adult, mature] = transpose

pprint(puppy)
pprint(junior)
pprint(adult)
pprint(mature)

Run the script above. You will get about the same result.

ViM: Python: Pretty Print: Extracted Stages

4: Material Colors

The colors

just like our pie chart, I set up material color variable in its own module.

Script

In order to keep my code clean. I put the name of each color as dictionary. The python script as usual:

material = {
  'red500'   : '#F44336',
  'pink500'  : '#E91E63',
  'purple500': '#9C27B0',
  'indigo500': '#3F51B5',
  'blue500'  : '#2196F3',
  'cyan500'  : '#00BCD4',
  'teal500'  : '#009688',
  'green500' : '#4CAF50',
  'lime500'  : '#CDDC39',
  'orange500': '#FF9800'
}

Very simple, and reuasble between barchart.

ViM: Python: Material Colors

That is all with colors.

What is Next 🤔?

Data structure is fun, but we have to move on.

Consider continue reading [ Matplotlib - Bar Chart - Part Two ].