1. CIT 383: Administrative Scripting
Arrays
CIT 383: Administrative Scripting

2. CIT 383: Administrative Scripting
Topics
Creating Arrays
Indexing Arrays
Array Methods
Iterators
CIT 383: Administrative Scripting

3. CIT 383: Administrative Scripting
Arrays in Ruby
a = [10, 20, 30, 40, 50, 60]
a[0] 10 20
a[1] 30
a[2]
a[3] 40
a[4] 50
a[5] 60
a[-1]
CIT 383: Administrative Scripting

4. CIT 383: Administrative Scripting
Arrays of Strings
Define the same way as arrays of integers
a = [‘spam’, ‘and’, ‘eggs’, ‘for’, ‘breakfast’]
Alternative syntax for strings w/o spaces:
a = %w[spam and eggs for breakfast]
a = %w|spam and eggs for breakfast|
%W works like double quoted strings
a = [“\t”, “\n”, “\r”]
a = %W(\t \n \r)
CIT 383: Administrative Scripting

5. CIT 383: Administrative Scripting
Creating Empty Arrays
Use the [] notation
a = []
Create like any other object
a = Array.new
Similar to
str = “”
str = String.new
CIT 383: Administrative Scripting

6. Arrays of Different Types
Ruby arrays can have data of different types
a=[1,2.718,‘a string’,“\t”,[3,4]]
Use like any other array
a[0] == 1
a[1] == 2.718
a[2] == ‘a string’
a[3] == “\t”
a[4] == [3, 4]
CIT 383: Administrative Scripting

7. CIT 383: Administrative Scripting
Indexing Arrays
Single indexes
a[n] is nth element from beginning starting at 0
a[-n] is nth element from end starting at -1
Double indexes (slicing)
a[0,1] == a[0]
a[0,2] == [ a[0], a[1] ]
a[1,3] == [ a[1], a[2], a[3] ]
a[-2, 2] == [ a[-2], a[-1] ]
CIT 383: Administrative Scripting

8. CIT 383: Administrative Scripting
Index Assignments
Single index
a[n] = 5 sets nth element to be 5
If a[n] isn’t already defined, extends array to be long enough to have an nth element.
Double index
a[0,2] = [10,20] sets first two elements to 10,20
a[0,0] = [1,2,3] inserts 3 elements at beginning
a[0,2] = [] deletes first two elements of array
CIT 383: Administrative Scripting

9. CIT 383: Administrative Scripting
Array Operations
Concatenation
a = [1,2,3] + [4,5] # [1,2,3,4,5]
a = a + [6,7,8] # [1,2,3,4,5,6,7,8]
Subtraction
[1,2,3,4,5,6] – [2,3,4] # [1,5,6]
Append
a = []
a << # [1]
a << 2 << # [1, 2,3]
a << [4,5,6] # [1,2,3,[4,5,6]]
CIT 383: Administrative Scripting

10. CIT 383: Administrative Scripting
Array Operations
Union: |
Concatenates then removes duplicates.
Intersection: &
Array of elements in both arrays, no duplicates.
Examples
a = [1,1,2,2,3,3,4]
b = [5,5,4,4,3,3,2]
a | b # [1,2,3,4,5]
b | a # [5,4,3,2,1]
a & b # [2,3,4]
b & a # [4,3,2]
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11. CIT 383: Administrative Scripting
Array Methods
reverse
Reverses order of array elements.
sort
Sorts array elements from lowest to highest
All array elements must be of same type.
sort!
Previous methods return altered array.
Methods ending in ! change array in place.
CIT 383: Administrative Scripting

12. Using Arrays w/o Indexing
We often need just a list of items to:
Add items from the list.
Remove items from the list.
Perform an action for each item of the list.
We don’t need to deal with indices since
The 5th item isn’t special.
We just want to add, remove, or do something for each item of the list.
Leaves only one choice: add and remove from
End of array (push and pop)
Beginning of array (shift and unshift)
CIT 383: Administrative Scripting

13. CIT 383: Administrative Scripting
Push and pop
push adds an element to end of array. 10
a[0]
a[0] 10 20 20
a.push(40) 30 30
a[-1] 40
a[-1]
CIT 383: Administrative Scripting

14. CIT 383: Administrative Scripting
Push and pop
pop removes an element from end of array. 10
a[0]
a[0] 10 20 20
x = a.pop 30
a[-1] 30
a[-1] 40
x == 40
CIT 383: Administrative Scripting

15. CIT 383: Administrative Scripting
Shift and unshift
unshift adds an element to start of array. 5
a[0]
a[0] 10 10 20
a.unshift(5) 20 30
a[-1] 30
a[-1]
CIT 383: Administrative Scripting

16. CIT 383: Administrative Scripting
Shift and unshift
shift removes an element f/ start of array. 10
a[0]
a[0] 5 20 10
x = a.shift 30
a[-1] 20
a[-1] 30
x == 5
CIT 383: Administrative Scripting

17. CIT 383: Administrative Scripting
The each iterator
Each executes code for each item of array
Assigns current element to |variable|
Executes block of code.
Sets current element to next element.
Example:
langs = %w(python ruby scheme)
langs.each do |language|
puts “#{language} is good.”
end
CIT 383: Administrative Scripting

18. CIT 383: Administrative Scripting
The each iterator
array.each do |var|
code
end
n = 0
var = array[n]
code
false
is n last element?
n = n + 1
true
CIT 383: Administrative Scripting

19. CIT 383: Administrative Scripting
References
Michael Fitzgerald, Learning Ruby, O’Reilly, 2008.
David Flanagan and Yukihiro Matsumoto, The Ruby Programming Language, O’Reilly, 2008.
Hal Fulton, The Ruby Way, 2nd edition, Addison-Wesley, 2007.
Dave Thomas with Chad Fowler and Andy Hunt, Programming Ruby, 2nd edition, Pragmatic Programmers, 2005.
CIT 383: Administrative Scripting