Answers questions 1-36

lib/questions.rb

@@ -1,152 +1,182 @@
 # keep only the elements that start with an a
 def select_elements_starting_with_a(array)
+  array.select { |word| word[0].downcase == 'a' }
 end
 
 # keep only the elements that start with a vowel
 def select_elements_starting_with_vowel(array)
+  array.select { |word| word[0].downcase[/([aeiou])/] }
 end
 
 # remove instances of nil (but NOT false) from an array
 def remove_nils_from_array(array)
+  array.compact!
 end
 
 # remove instances of nil AND false from an array
 def remove_nils_and_false_from_array(array)
+  remove_nils_from_array(array).reject { |value| value == false }
 end
 
 # don't reverse the array, but reverse every word inside it. e.g.
 # ['dog', 'monkey'] becomes ['god', 'yeknom']
 def reverse_every_element_in_array(array)
+  array.map { |value| value.reverse  }
 end
 
 # given an array of student names, like ['Bob', 'Dave', 'Clive']
 # give every possible pairing - in this case:
 # [['Bob', 'Clive'], ['Bob', 'Dave'], ['Clive', 'Dave']]
 # make sure you don't have the same pairing twice,
 def every_possible_pairing_of_students(array)
+  array.combination(2)
 end
 
 # discard the first 3 elements of an array,
 # e.g. [1, 2, 3, 4, 5, 6] becomes [4, 5, 6]
 def all_elements_except_first_3(array)
+  array.select {|el| array.index(el) > 2 }
 end
 
 # add an element to the beginning of an array
 def add_element_to_beginning_of_array(array, element)
+  array.unshift(element)
 end
 
 # sort an array of words by their last letter, e.g.
 # ['sky', 'puma', 'maker'] becomes ['puma', 'maker', 'sky']
 def array_sort_by_last_letter_of_word(array)
+  array.sort_by { |word| word[-1] }
 end
 
 # cut strings in half, and return the first half, e.g.
 # 'banana' becomes 'ban'. If the string is an odd number of letters
 # round up - so 'apple' becomes 'app'
 def get_first_half_of_string(string)
+  midpoint = (string.length.to_f / 2).ceil
+  string[0...(midpoint)]
 end
 
 # turn a positive integer into a negative integer. A negative integer
 # stays negative
 def make_numbers_negative(number)
+  -(number.abs)
 end
 
 # turn an array of numbers into two arrays of numbers, one an array of
 # even numbers, the other an array of odd numbers
 # even numbers come first
 # so [1, 2, 3, 4, 5, 6] becomes [[2, 4, 6], [1, 3, 5]]
 def separate_array_into_even_and_odd_numbers(array)
+  [array.select { |el| el.even? }, array.select { |el| el.odd? } ]
 end
 
-# count the numbers of elements in an element which are palindromes
+# count the numbers of elements in an array which are palindromes
 # a palindrome is a word that's the same backwards as forward
 # e.g. 'bob'. So in the array ['bob', 'radar', 'eat'], there
 # are 2 palindromes (bob and radar), so the method should return 2
 def number_of_elements_that_are_palindromes(array)
+  (array & reverse_every_element_in_array(array)).length
 end
 
 # return the shortest word in an array
 def shortest_word_in_array(array)
+  array.min
 end
 
-# return the shortest word in an array
+# return the longest word in an array
 def longest_word_in_array(array)
+  array.max { |a,b| a.length <=> b.length }
 end
 
 # add up all the numbers in an array, so [1, 3, 5, 6]
 # returns 15
 def total_of_array(array)
+  array.sum
 end
 
 # turn an array into itself repeated twice. So [1, 2, 3]
 # becomes [1, 2, 3, 1, 2, 3]
 def double_array(array)
+  array + array
 end
 
 # convert a symbol into a string
 def turn_symbol_into_string(symbol)
+  symbol.to_s
 end
 
 # get the average from an array, rounded to the nearest integer
 # so [10, 15, 25] should return 17
 def average_of_array(array)
+  (array.sum.to_f / array.length).ceil
 end
 
 # get all the elements in an array, up until the first element
 # which is greater than five. e.g.
 # [1, 3, 5, 4, 1, 2, 6, 2, 1, 3, 7]
 # becomes [1, 3, 5, 4, 1, 2]
 def get_elements_until_greater_than_five(array)
+  array.take_while { |element| element <= 5}
 end
 
 # turn an array (with an even number of elements) into a hash, by
 # pairing up elements. e.g. ['a', 'b', 'c', 'd'] becomes
 # {'a' => 'b', 'c' => 'd'}
 def convert_array_to_a_hash(array)
+  Hash[*array]
 end
 
 # get all the letters used in an array of words and return
 # it as a array of letters, in alphabetical order
 # . e.g. the array ['cat', 'dog', 'fish'] becomes
 # ['a', 'c', 'd', 'f', 'g', 'h', 'i', 'o', 's', 't']
 def get_all_letters_in_array_of_words(array)
+  array.join.split('').sort.uniq
 end
 
 # swap the keys and values in a hash. e.g.
 # {'a' => 'b', 'c' => 'd'} becomes
 # {'b' => 'a', 'd' => 'c'}
 def swap_keys_and_values_in_a_hash(hash)
+  hash.invert
 end
 
 # in a hash where the keys and values are all numbers
 # add all the keys and all the values together, e.g.
 # {1 => 1, 2 => 2} becomes 6
 def add_together_keys_and_values(hash)
+  hash.flatten.sum
 end
 
 # take out all the capital letters from a string
 # so 'Hello JohnDoe' becomes 'ello ohnoe'
 def remove_capital_letters_from_string(string)
+  string.gsub(/[A-Z]/, '')
 end
 
 # round up a float up and convert it to an Integer,
 # so 3.214 becomes 4
 def round_up_number(float)
+  float.ceil
 end
 
 # round down a float up and convert it to an Integer,
 # so 9.52 becomes 9
 def round_down_number(float)
+  float.to_i
 end
 
 # take a date and format it like dd/mm/yyyy, so Halloween 2013
 # becomes 31/10/2013
 def format_date_nicely(date)
+  date.strftime('%d/%m/%Y')
 end
 
 # get the domain name *without* the .com part, from an email address
 # so alex@makersacademy.com becomes makersacademy
 def get_domain_name_from_email_address(email)
+  email.split('@')[1].split('.')[0]
 end
 
 # capitalize the first letter in each word of a string,
@@ -155,30 +185,41 @@ def get_domain_name_from_email_address(email)
 # 'the lion the witch and the wardrobe' becomes
 # 'The Lion the Witch and the Wardrobe'
 def titleize_a_string(string)
+  excluded_words = %w(the and a)
+  string.capitalize.gsub(/\w+/) do |word|
+    excluded_words.include?(word) ? word : word.capitalize
+  end
 end
 
 # return true if a string contains any special characters
 # where 'special character' means anything apart from the letters
 # a-z (uppercase and lower) or numbers
 def check_a_string_for_special_characters(string)
+  /\W/ === string
 end
 
 # get the upper limit of a range. e.g. for the range 1..20, you
 # should return 20
 def get_upper_limit_of(range)
+  range.max
 end
 
 # should return true for a 3 dot range like 1...20, false for a
 # normal 2 dot range
 def is_a_3_dot_range?(range)
+  range.exclude_end?
 end
 
 # get the square root of a number
 def square_root_of(number)
+  Math.sqrt(number)
 end
 
 # count the number of words in a file
 def word_count_a_file(file_path)
+  file = File.open(file_path, "rb")
+  contents = file.read
+  contents.split.count
 end
 
 # --- tougher ones ---
@@ -187,6 +228,7 @@ def word_count_a_file(file_path)
 # called call_method_from_string('foobar')
 # the method foobar should be invoked
 def call_method_from_string(str_method)
+  this.str_method
 end
 
 # return true if the date is a uk bank holiday for 2014