Populating an array from another array

Question

I would like to create an array with the first letter from each element, but I keep just getting the entire element - what am I doing wrong?

def each_group_by_first_letter
  self.each do |x| 
    first_letter = []
    first_letter = x[0, 1].to_s
  end

  x = ["abcd", "efgh", "able"]
  x.each_group_by_first_letter do |letter, words|
    printf("%s: %s\n", letter, words)
  end

First of all, you need another end here somewhere. I deduce that you meant it to be before the line x = ["abcd".... — Jacob Mattison
– Jacob Mattison, Commented Nov 15, 2011 at 4:57
yes...i cut down the code to the relevant parts...there is another end in there... — user1043856
– user1043856, Commented Nov 15, 2011 at 5:05
Well, your each_group_by_first_letter isn't returning anything explicitly, so in this case it's just returning self. — Jacob Mattison
– Jacob Mattison, Commented Nov 15, 2011 at 5:11

Jordan Running · Accepted Answer · 2011-11-15 05:24:31Z

8

There are several problems with your code. Among them:

You create an array called first_letter, but then overwrite it with a string on the next line instead of adding the string to it. (To add an item to an array you will usually use Array#push or Array#<<.)
You don't return first_letter, which means you're implicitly returning the array itself (assuming that's what self is--because that's what Array#each returns).
When you call each_group_by_first_letter you pass it a block (do ...) but your method doesn't take or use a block. You probably mean to call each on the result of each_group_by_first_letter.

Regardless, the Array class already has the tools you need--no need to define a new method for this.

x = [ 'abcd', 'efgh', 'able' ]

x.map {|word| word[0] }
# => [ 'a', 'e', 'a' ]

edited Nov 15, 2011 at 5:24

answered Nov 15, 2011 at 5:14

Jordan Running

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Comments

Tilo · Accepted Answer · 2011-11-15 05:23:58Z

3

x = ["abcd", "efgh", "able"]
y = x.map{|e| e[0]}          # keeps x intact

or

x = ["abcd", "efgh", "able"]
x.map!{|e| e[0]}             # modifies x

 => ["a", "e", "a"]

edited Nov 15, 2011 at 5:23

answered Nov 15, 2011 at 5:15

Tilo

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