Introduction
Suppose you want all the non-negative integers up to 1000.
It would be ridiculous if you had to type these into an array.
For this we have the range type:
julia> 0:1000
0:1000
julia> typeof(0:1000)
UnitRange{Int64}
Ranges are very common: not just to save you typing, but also as return types from functions.
Note that ranges are not vectors.
They are just a set of instructions to generate a sequence ("lazy" evaluation, or an "iterator").
If you need a range as a vector, use the collect() function for conversion:
julia> collect(0:5)
6-element Vector{Int64}:
0
1
2
3
4
5
The step size can be specified, in this case 0.3:
julia> collect(1.0:0.3:2.0)
4-element Vector{Float64}:
1.0
1.3
1.6
1.9
So the syntax is start:stepsize:stop.
Both end limits are inclusive, as seen in the integer example.
If the step size does not divide exactly into stop - start, the last element will avoid exceeding stop.
Letter ranges
Non-numeric sequences can also be used in ranges.
The simplest example is ASCII letters:
julia> 'a':'d'
'a':1:'d'
julia> typeof('a':'d')
StepRange{Char, Int64}
julia> collect('a':'d')
4-element Vector{Char}:
'a': ASCII/Unicode U+0061 (category Ll: Letter, lowercase)
'b': ASCII/Unicode U+0062 (category Ll: Letter, lowercase)
'c': ASCII/Unicode U+0063 (category Ll: Letter, lowercase)
'd': ASCII/Unicode U+0064 (category Ll: Letter, lowercase)
The Char type will be covered in more detail in another Concept.
For now, just treat these as single characters in single-quotes.
Functions and operators for ranges
Check the limits of a range with first() and last().
r = 1:10 # => 1:10
first(r) # => 1
last(r) # => 10
More on vector indexing
Integer ranges and vectors can be used in vector indexing:
nums = collect(10.0:50.0)
nums[3:2:7] # gives [12.0, 14.0, 16.0]
nums[ [3, 5, 7] ] # also gives [12.0, 14.0, 16.0]
Instructions
As a chess enthusiast, you would like to write your own version of the game. Yes, there maybe plenty of implementations of chess available online already, but yours will be unique!
But before you can let your imagination run wild, you need to take care of the basics. Let's start by generating the board.
Each square of the chessboard is identified by a letter-number pair. The vertical columns of squares, called files, are labeled A through H. The horizontal rows of squares, called ranks, are numbered 1 to 8.
1. Define the rank range
Implement the rank_range() function. It should return a range of integers, from 1 to 8.
julia> rank_range()
# output omitted
2. Define the file range
Implement the file_range() function.
It should return a range of characters, from the uppercase letter A, to the uppercase letter H.
julia> file_range()
# output omitted
Implement the ranks() function. It should return a vector of integers, from 1 to 8.
Do not write the vector by hand, generate it from the range returned by the rank_range() function.
julia> ranks()
[1, 2, 3, 4, 5, 6, 7, 8]
Implement the files function. It should return a vector of characters, from 'A' to 'H'.
Do not write the vector by hand, generate it from the range returned by the file_range() function.
julia> files()
['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H']
Learning Exercise
