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annotate 1-Ruby/day2.rb @ 46:eac30c1b92da

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Add more notes and try to understand the operators
author IBBoard <dev@ibboard.co.uk>
date Wed, 20 Sep 2017 20:48:37 +0100
parents 25c15f27b33d
children
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1 #! /usr/bin/env ruby
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2
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3 ## File handling with a block
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4 name = 'day2.txt'
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5
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6 def print_file(name)
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7 File.open(name, 'r') do |file|
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8 puts name
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9 while line = file.gets
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10 puts " #{line}"
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11 end
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12 end
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13 end
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14
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15 File.open(name, 'w') do |file|
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16 file.puts "File contents go here"
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17 end
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18 print_file(name)
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19 File.open(name, 'r+') do |file|
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20 # If we don't seek then we override
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21 file.seek(0, IO::SEEK_END)
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22 file.puts 'Extra content here'
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23 end
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24 print_file(name)
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25 File.delete(name)
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26
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27 puts "File still exists!" if File.exists?(name)
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28
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29 # Old-skool Java style without passing a code block
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30 my_file = File.open(name, 'w')
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31 my_file.puts 'Non-block file content'
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32 my_file.close() #Note: Close the file manually!
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33 print_file(name)
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34 File.delete(name)
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35
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36 ## Converting a hash into an array
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37 my_hash = { 'a' => 'one', 'b' => 'two', 'c' => 'three' }
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38 puts my_hash.inspect
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39 # "{}.methods" includes "to_a" method - appears to convert to an array.
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40 puts my_hash.to_a.inspect
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41 # However, it includes keys *and* values (as nested arrays, according to http://apidock.com/ruby/Hash/to_a).
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42 # There's also ":keys" and ":values"
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43 puts my_hash.keys.inspect
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44 puts my_hash.values.inspect
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45 # Alternatively, :collect runs over all key-value pairs as an array, so we can do:
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46 puts my_hash.collect { |val| val[1] }.inspect
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47
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48 ## Converting an array to a hash
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49 # Arrays have a :to_h method, but that assumes nested arrays of key-value pairs,
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50 # e.g. [[key1, value1], [key2, value2]]
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51 # Looping to create a nested array structure then :to_h would work:
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52 my_array = ['one', 'two', 'three']
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53 temp = []
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54 # This would be neater with :map or :collect but then we don't get the index.
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55 # The only sensible option is an :each_with_index, but that negates the need
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56 # for :to_h.
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57 my_hash = {}
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58 my_array.each_with_index do |val, idx|
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59 my_hash[idx] = val
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60 end
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61 puts my_hash.inspect
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62
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63 ## Iterating a hash
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64 puts "Each with single parameter gets pairs"
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65 my_hash.each { |vals| puts "++#{vals[0]} = #{vals[1]}" }
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66 puts "Each with two parameters gets key and value"
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67 my_hash.each { |key, val| puts "++#{key} = #{val}" }
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68 puts "Or you can get just keys and just values"
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69 my_hash.each_key { |key| puts "++#{key}" }
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70 my_hash.each_value { |value| puts "++#{value}" }
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71
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72 ## Arrays as stacks:
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73 my_arr = []
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74 my_arr.push(1)
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75 my_arr.push(2)
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76 my_arr.push(3)
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77 my_arr.push(4)
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78 puts my_arr.pop()
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79 puts my_arr.pop()
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80 puts my_arr.pop()
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81 puts my_arr.pop()
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82 ## Arrays as queues
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83 my_arr.push(7)
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84 my_arr.push(8)
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85 my_arr.push(9)
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86 my_arr.push(10)
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87 puts my_arr.shift()
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88 puts my_arr.shift()
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89 puts my_arr.shift()
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90 puts my_arr.shift()
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91
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92 ## Iterating in fours
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93
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94 my_arr = Array(1..16)
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95 # We need a temp place holder - we can't do ugly things with indexes
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96 temp = []
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97 my_arr.each do |val|
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98 temp.push(val)
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99 if temp.size == 4
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100 puts "#{temp[0]} #{temp[1]} #{temp[2]} #{temp[3]}"
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101 temp = []
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102 end
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103 end
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104
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105 ## And with each_slice
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106 my_arr.each_slice(4) do |val|
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107 puts "#{val[0]} #{val[1]} #{val[2]} #{val[3]}"
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108 end
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109