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Students continue practicing their Design Recipe skills, making lots of simple functions dealing with the Animals Dataset. Then they learn how to chain Methods together, and define more sophisticated subsets.

Prerequisites

Defining Table Functions

Relevant Standards

Select one or more standards from the menu on the left (⌘-click on Mac, Ctrl-click elsewhere).

CSTA Standards
2-AP-13

Decompose problems and subproblems into parts to facilitate the design, implementation, and review of programs

2-AP-17

Systematically test and refine programs using a range of test cases

3A-AP-17

Decompose problems into smaller components through systematic analysis, using constructs such as procedures, modules, and/or objects.

3A-AP-18

Create artifacts by using procedures within a program, combinations of data and procedures, or independent but interrelated programs.

K-12CS Standards
6-8.Algorithms and Programming.Control

Programmers select and combine control structures, such as loops, event handlers, and conditionals, to create more complex program behavior.

9-12.Algorithms and Programming.Control

Programmers consider tradeoffs related to implementation, readability, and program performance when selecting and combining control structures.

9-12.Algorithms and Programming.Modularity

Complex programs are designed as systems of interacting modules, each with a specific role, coordinating for a common overall purpose. These modules can be procedures within a program; combinations of data and procedures; or independent, but interrelated, programs. Modules allow for better management of complex tasks.

P3

Recognizing and Defining Computational Problems

Next-Gen Science Standards
HS-SEP4-1

Analyze data using tools, technologies, and/or models (e.g., computational, mathematical) in order to make valid and reliable scientific claims or determine an optimal design solution.

Oklahoma Standards
OK.L1.AP.M.01

Break down a solution into procedures using systematic analysis and design.

Lesson Goals

Students will be able to…​

  • Use method chaining to write more sophisticated analyses using less code

  • Identify bugs introduced by chaining methods in the wrong order

Student-facing Lesson Goals

  • Let’s practice writing functions and combining methods together.

Materials

Preparation

  • Make sure all materials have been gathered

  • Decide how students will be grouped in pairs

  • Computer for each student (or pair), with access to the internet* All students should log into CPO and open the "Animals Starter File" they saved from the prior lesson. If they don’t have the file, they can open a new one

  • Student workbook, and something to write with

Supplemental Resources

Language Table

Types

Functions

Values

Number

num-sqrt, num-sqr, mean, median, modes

4, -1.2, 2/3

String

string-repeat, string-contains

"hello", "91"

Boolean

==, <, <=, >=, string-equal

true, false

Image

triangle, circle, star, rectangle, ellipse, square, text, overlay, bar-chart, pie-chart, bar-chart-summarized, pie-chart-summarized

🔵🔺🔶

Table

count, .row-n, order-by, .filter, .build-column

🔗Design Recipe Practice 25 minutes

Overview

Students practice more of what they learned in the previous lesson, applying the Design Recipe to simple table functions that operate on rows of the Animals Dataset. The functions they create - in addition to the ones they’ve already made - set up the method-chaining activity.

Launch

The Design Recipe is a powerful tool for solving problems by writing functions. It’s important for this to be like second nature, so let’s get some more practice using it!

Investigate

Define the Compute functions on The Design Recipe (Page 32) and The Design Recipe (Page 33).

Synthesize

Did students find themselves getting faster at using the Design Recipe? Can students share any patterns they noticed, or shortcuts they used?

🔗Chaining Methods 25 minutes

Overview

Students learn how to perform multiple table operations (sorting, filtering, building) in the same line of code.

Launch

Now that we are doing more sophisticated analyses, we might find ourselves writing the following code:

# get a table with the nametags of all the fixed animals, ordered by species
with-labels = animals-table.build-column("labels", nametag)
fixed-with-labels = with-nametags.filter(is-fixed)
result = fixed-with-labels.order-by("species", true)

That’s a lot of code, and it also requires us to come up with names for each intermediate step! Pyret allows table methods to be chained together, so that we can build, filter and order a Table in one shot. For example:

# get a table with the nametags of all the fixed animals, ordered by species
result = animals-table.build-column("labels", nametag).filter(is-fixed).order-by("species", true)

This code takes the animals-table, and builds a new column. According to our Contracts Page, .build-column produces a new Table, and that’s the Table whose .filter method we use. That method produces yet another Table, and we call that Table’s order-by method. The Table that comes back from that is our final result.

Teaching Tip

Use different color markers to draw nested boxes around each part of the expression, showing where each Table came from.

It can be difficult to read code that has lots of method calls chained together, so we can add a line-break before each “.” to make it more readable. Here’s the exact same code, written with each method on its own line:

# get a table with the nametags of all the fixed animals, order by species
animals-table
  .build-column("label", nametag)
  .filter(is-fixed)
  .order-by("species", true)

Order matters: Build, Filter, Order.

Suppose we want to build a column and then use it to filter our table. If we use the methods in the wrong order (trying to filter by a column that doesn’t exist yet), we might wind up crashing the program. Even worse, the program might work, but produce results that are incorrect!

Investigate

When chaining methods, it’s important to build first, then filter, and then order.

How well do you know your table methods? Complete Chaining Methods (Page 34) and Chaining Methods 2: Order Matters! (Page 35) in your Student Workbook to find out.

Synthesize

As our analysis gets more complex, method chaining is a great way to keep the code simple. But complex analysis also has more room for mistakes, so it’s critical to think carefully when we use it!

These materials were developed partly through support of the National Science Foundation, (awards 1042210, 1535276, 1648684, and 1738598). CCbadge Bootstrap:Data Science by Emmanuel Schanzer, Nancy Pfenning, Emma Youndtsmith, Jennifer Poole, Shriram Krishnamurthi, Joe Politz, Ben Lerner, Flannery Denny, and Dorai Sitaram with help from Eric Allatta and Joy Straub is licensed under a Creative Commons 4.0 Unported License. Based on a work at www.BootstrapWorld.org. Permissions beyond the scope of this license may be available by contacting schanzer@BootstrapWorld.org.