2.9 Intro to Data Science: Basic Descriptive Statistics

  • In data science, you’ll often use statistics to describe and summarize your data.
  • Here, we introduce several descriptive statistics:
    • minimum—the smallest value in a collection of values.
    • maximum—the largest value in a collection of values.
    • range—the range of values from the minimum to the maximum.
    • count—the number of values in a collection.
    • sum—the total of the values in a collection.

Determining the Minimum of Three Values

  • Determine the minimum of three values manually in a script that prompts for and inputs three values, uses if statements to determine the minimum value, then displays it.
# fig02_02.py
"""Find the minimum of three values."""

number1 = int(input('Enter first integer: '))
number2 = int(input('Enter second integer: '))
number3 = int(input('Enter third integer: '))

minimum = number1

if number2 < minimum:
    minimum = number2

if number3 < minimum:
    minimum = number3

print('Minimum value is', minimum)
  • Enter 12, 27 and 36
In [1]:
run fig02_02.py

Minimum value is 12
  • Enter 12, 36 and 27
In [2]:
run fig02_02.py

Minimum value is 12
  • Enter 36, 27 and 12
In [3]:
run fig02_02.py

Minimum value is 12
  • Logic of determining minimum:
    • First, assume that number1 contains the smallest value.
    • The first if statement then tests number2 < minimum and if this condition is True assigns number2 to minimum.
    • The second if statement then tests number3 < minimum, and if this condition is True assigns number3 to minimum.
  • Now, minimum contains the smallest value, so we display it.

Determining the Minimum and Maximum with Built-In Functions min and max (1 of 2)

  • Python has many built-in functions for performing common tasks.
  • min and max calculate the minimum and maximum, respectively, of a collection of values.

Determining the Minimum and Maximum with Built-In Functions min and max (2 of 2)

In [4]:
min(36, 27, 12)
Out[4]:
12
In [5]:
max(36, 27, 12)
Out[5]:
36

Determining the Range of a Collection of Values (1 of 2)

  • The range of values is simply the minimum through the maximum value.
  • Much data science is devoted to getting to know your data.

Determining the Range of a Collection of Values (2 of 2)

  • Have to understand how to interpret statistics.
    • If you have 100 numbers with a range of 12 through 36, those numbers could be distributed evenly over that range.
    • At the opposite extreme, you could have clumping with 99 values of 12 and one 36, or one 12 and 99 values of 36.

Functional-Style Programming: Reduction

  • We introduce various functional-style programming capabilities.
  • These enable you to write code that can be more concise, clearer and easier to debug.
  • Functions min and max are examples of a functional-style programming concept called reduction—each reduces a collection of values to a single value.
  • Other reductions you'll see: sum, average, variance and standard deviation.

©1992–2020 by Pearson Education, Inc. All Rights Reserved. This content is based on Chapter 2 of the book Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and the Cloud.

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