Update the Hashes and Arrays Resource #362

droberts-sea · 2018-01-22T18:11:51Z

Description

Restructure the Arrays and Hashes lecture

There are now 3 main sections: Arrays, Hashes, and In Combination. Each section has the same basic layout:

Creation
Accessing elements
Iteration

which I think gives it a really nice flow and emphasizes the pattern.

In between arrays / hashes and in combination is a comparison section, where I moved the table I made in the previous commit.

I've also reworked the examples away from Pokemon, since we got so many freaking complaints last time.

We may want to assign the first 3 sections (arrays, hashes, comparison) as homework the night before, depending on time.

Todos

Build the pre-reading into the calendar

Feedback Requested

Find my dopey typos!

There are now 3 main sections: Arrays, Hashes, and In Combination. Each section has the same basic layout: - Creation - Accessing elements - Iteration which I think gives it a really nice flow and emphasizes the pattern. In between arrays / hashes and in combination is a comparison section, where I moved the table I made in the previous commit. I've also reworked the examples away from Pokemon, since we got so many freaking complaints last time. We may want to assign the first 3 sections (arrays, hashes, comparison) as homework the night before, depending on time.

droberts-sea · 2018-01-25T00:08:48Z

C9 Week 1: Consolidate initial treatment of Arrays and Hashes

CheezItMan · 2018-01-25T17:10:58Z

01-ruby-fundamentals/data-structures.md

+  - The list can be empty
+- Since an array is an object, we can store it in a variable
+- You can get the length of the array with `Array#length`
+- The array will keep track of the order elements were added


I think it's better, it maintains the original order of the elements given.

CheezItMan · 2018-01-25T17:21:01Z

01-ruby-fundamentals/data-structures.md

+  - The list can be empty
+- Since a hash is an object, we can store it in a variable
+- You can get the number of key/value pairs with `Hash#length`
+- The hash does **not** keep track of the order of its key/value pairs


I think technically ruby does now maintain the order of the key/value pairs.

http://ruby-doc.org/core-2.5.0/Hash.html

I think it makes more sense to talk about why you shouldn't worry about order in a Hash.

You're right, it's not mandated by the spec but it does happen in practice. I've struggled with this because ordering is not a property of hashes in general, only in this particular implementation of ruby, and I don't want to set them up with bogus expectations.

There's probably a better way to address this, and I think you're right that it involves talking about the "why" of it.

CheezItMan · 2018-01-25T17:25:23Z

01-ruby-fundamentals/data-structures.md

+#### Iteration
+
+- Like an array, you can iterate through the key/value pairs in a hash
+  - Unlike an array, the order is not guaranteed


Again I think it is in the order they were inserted.

tildeee

👍

tildeee · 2018-01-25T18:54:02Z

01-ruby-fundamentals/data-structures.md


-This loop does the same thing with slightly different syntax.  
+- Iteration is the process of doing something to each element in the array, like printing it to the command line or adding 7 to it
+- To iterate manually, you can use a `times` loop on the length of the array


What does "to iterate manually"?

kariabancroft · 2018-01-25T18:51:42Z

01-ruby-fundamentals/data-structures.md

-You've dealt with variables holding a single value and you've been introduced to the concept of collections as well, but here we'll go into greater depth.  
+# Intro to Data Structures: Arrays and Hashes
+
+<!--


This would be a great note for the TET

kariabancroft · 2018-01-25T18:55:01Z

01-ruby-fundamentals/data-structures.md

+- Arrays are created by putting square brackets `[]` around a list of things
+  - The list can be empty
+- Since an array is an object, we can store it in a variable
+- You can get the length of the array with `Array#length`


While this method declaration syntax is accurate, it is often confusing for the students, especially early on. Do we need to use this or could we just show them the dot methods?

kariabancroft · 2018-01-25T18:57:20Z

01-ruby-fundamentals/data-structures.md


-# Accessing the first element
-puts my_list[0]
+puts "#{students}"


Why use string interpolation instead of puts-ing the array directly? (as a question i would want to know why)

For arrays and hashes, puts with interpolation will put it on one line with brackets, making it much more visually obvious (IMO) what's going on. Puts with no interpolation will split it across many lines with no brackets.

myarr = [1, 2, 3] puts myarr # Output: # 1 # 2 # 3 puts "#{myarr}" # Output: # [1, 2, 3]

kariabancroft · 2018-01-25T18:58:05Z

01-ruby-fundamentals/data-structures.md

+- Each element in the array is assigned a number called its _index_
+  - Indices always start from 0
+  - This means the last element is at `arr.length - 1`
+  - Negative indices count backwards from the end, starting at `-1`


Could you add that this would be the last element in the array just to clarify

kariabancroft · 2018-01-25T18:58:42Z

01-ruby-fundamentals/data-structures.md

+- You can add a new element to the array with the `Array#push` method or with `<<`
+- You can read elements using square brackets `[]` and the index
+- Changing the value of an element is done in the same way
+- Trying to read an element that doesn't exist will result in `nil`


"read an element at an index that is not in the array"

kariabancroft · 2018-01-25T19:01:17Z

01-ruby-fundamentals/data-structures.md


-This loop does the same thing with slightly different syntax.  
+- Iteration is the process of doing something to each element in the array, like printing it to the command line or adding 7 to it


I might leave off the 'like printing it' section

kariabancroft · 2018-01-25T19:02:06Z

01-ruby-fundamentals/data-structures.md


-This loop does the same thing with slightly different syntax.  
+- Iteration is the process of doing something to each element in the array, like printing it to the command line or adding 7 to it
+- To iterate manually, you can use a `times` loop on the length of the array


Maybe describe what this does differently (using the index) rather than using "manually"

kariabancroft · 2018-01-25T19:21:03Z

01-ruby-fundamentals/data-structures.md

-The Array has the following index/value pairs.
+fruit_prices = {
+  apple: 2.15,
+  pear: 3.02,


Do we prefer the trailing comma? I feel like do in JS but not in Ruby

The community style guide suggests avoiding trailing commas.

https://github.com/bbatsov/ruby-style-guide#no-trailing-array-commas

Good question. This is why we need a style guide.

Rubocop says no by default, but you can make it OK for multiline literals
rubocop/rubocop#713

Crap chris had already answered this when I hit send. I guess our conclusions are the same - I'll remove the trailing commas.

kariabancroft · 2018-01-25T19:28:59Z

01-ruby-fundamentals/data-structures.md

+  {
+    name: 'quiche',
+    price: 10.00,
+    allergens: ['gluten', 'dairy',],


Same question re trailing commas

kariabancroft · 2018-01-25T19:31:06Z

01-ruby-fundamentals/intro-to-object-types.md

+
+
+
+
 Look at the Ruby docs for [Array](http://www.ruby-doc.org/core-2.4.0/Array.html) and [Hash](http://www.ruby-doc.org/core-2.4.0/Hash.html) for more details about collections.


We should update these links to not reference the specific version but reference the latest by just using /core/ instead

Dan Roberts added 3 commits January 16, 2018 13:00

Add table comparing arrays and hashes

92f9e97

Add comment about how first half of arrays/hashes should be pre-reading

1a33e1f

droberts-sea requested review from CheezItMan and tildeee January 22, 2018 18:12

droberts-sea self-assigned this Jan 22, 2018

Minor wording change

ee53dc8

CheezItMan reviewed Jan 25, 2018

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tildeee approved these changes Jan 25, 2018

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kariabancroft reviewed Jan 25, 2018

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Dan Roberts added 2 commits January 28, 2018 13:34

Merge remote-tracking branch 'origin/master' into dpr/c9-hashes-arrays

d1e044e

Respond to PR comments

421ba42

kariabancroft approved these changes Feb 1, 2018

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droberts-sea merged commit b639b91 into master Feb 2, 2018

droberts-sea deleted the dpr/c9-hashes-arrays branch February 2, 2018 00:25

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Update the Hashes and Arrays Resource #362

Update the Hashes and Arrays Resource #362

droberts-sea commented Jan 22, 2018 •

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		This loop does the same thing with slightly different syntax.
		- Iteration is the process of doing something to each element in the array, like printing it to the command line or adding 7 to it





		Look at the Ruby docs for [Array](http://www.ruby-doc.org/core-2.4.0/Array.html) and [Hash](http://www.ruby-doc.org/core-2.4.0/Hash.html) for more details about collections.

Update the Hashes and Arrays Resource #362

Update the Hashes and Arrays Resource #362

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droberts-sea commented Jan 22, 2018 • edited Loading

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droberts-sea commented Jan 22, 2018 •

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