Indicator Functions

JMU

Indicator Functions
A Programming Pattern (With Examples in Python)

Prof. David Bernstein
James Madison University

Computer Science Department

bernstdh@jmu.edu

Motivation

The Idea:
- Problems in which an indicator’s value must be calculated before it can be used in another expression
An Example:
- "The show must go on" (i.e., the number of seats sold for a particular show time must be used to calculate an indicator, setting it to 0 when no tickets have been sold and setting it to 1 otherwise)

Review

A Specific Solution that Leads to Code Duplication:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: review0)
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A Better Specific Solution:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: review1)
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The Pattern

A General Solution for Threshold Indicators:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: indicator)
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Other General Solutions:
- The parameters of the method and the logic in the body of the method vary with the problem

Examples of Threshold Indicators

The Show Must Go On:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: shows)
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Parking Tickets:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: parking)
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Another Example

Basic Metabolic Rate (BMR):
- \(b = 5.00 + 10.00 m + 6.25 h - 5.00 a - 161.00 \delta_f \)
The Indicator Method:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: female)
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Using the Indicator Method:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: bmr)
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A Warning

Don't Overgeneralize:
- This pattern is often not appropriate for boolean methods
An Inappropriate Use of the Pattern:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: old0)
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The Appropriate Solution:
- pythonexamples/programmingpatterns/IndicatorFunctions.py (Fragment: old1)
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