String replacement using gsub or sub

Question

I am studying for an exam tomorrow. One of the previous questions was to define a method to add a e to an array element (array of symbols) if the element ended with a or add an s if it ended with i.

Without using gsub or sub I can do this fine:

arbitrary = [:alpha, :beta, :kappa, :phi]
p arbitrary

def pluralise (array)
  manipulate = []
  array.each {|member|
    string = member.to_s
    last_char = string[-1,1]
    if last_char == "a" then
      string = string + "e"
      manipulate << string.to_sym
    end
    if last_char == "i" then
      string = string + "s"
      manipulate << string.to_sym
    end

  }
  manipulate

end

new_arbitrary = pluralise(arbitrary)

p new_arbitrary

However, attempting this with gsub or sub does not change the array:

arbitrary = [:alpha, :beta, :kappa, :phi]
p arbitrary

def pluralisesub (array)
  manipulate = []
  array.each {|member|
    string = member.to_s    
    last_char = string[-1,1]
    if last_char == "a" then
      string.gsub(string, string + "s")
      manipulate << string.to_sym
    end
    if last_char == "i" then
      string.gsub(string,string + "s")
      manipulate << string.to_sym
    end

  }
  manipulate

end

new_arbitrary = pluralisesub(arbitrary)

p new_arbitrary

Does anybody have any ideas what is going wrong here?

Thanks

Answer 1

Modify the line string.gsub(string, string + "s") to string.gsub!(string, string + "s"). It will work.

String#gsub works on the copy of the receiver, where as String.gsub! works on the receiver itself.

Answer 2

You can do the entire find and replace on in array in a map and case statement.

[:alpha, :beta, :kappa, :phi].map do |v|
  v = v.to_s
  case v[-1]
  when 'a' then v + 'e'
  when 'i' then v + 's'
  else v
  end
end