Flashback time. We are in 1999 and you are coding in ASP thinking that this language is the future. You use ADODB recordsets to iterate over collections. You have a recordset containing some records from a “quotes” table. The “quotes” table contains a author column (varchar) and a body column (varchar). Now you want to display the results grouped by author name so it looks like this :

Georges Brassens
- Les filles quand ça dit “je t’aime”, c’est comme un second baptême
- Aucune idée sur terre n’est digne d’un trépas

Billie Holiday
- Don’t threaten me with love, baby. Let’s just go walking in the rain.
- I never hurt nobody but myself and that’s nobody’s business but my own.

Assuming your recordset is ordered by author, you do something like this (remember, we’re in 1999) :

Ok welcome back in 2008. ASP is dead. You are coding in rails and you want to do the same thing. How will you do it? Storing the author name in a buffer variable like in 1999? Not too sure about it.

This is a job for Enumerable#group_by (Enumerable is a module that is mixed in the Array class)

Enumerable#group_by will create different sets of quotes based on the “author” values. Why the “&” sign? It’s because group_by expects a block. I could have done it this way : @authors = all_quotes.group_by{|quote| quote.author}

So @authors is now a hash that will look like this:

{”George Brassens” => [#<Quote id:131 …>, #<Quote id:331 …>], “Billie Holiday” => [#<Quote id:111 …>, #<Quote id:911 …>] }

Now you can iterate over it like this :

One more thing to note : @authors is a hash, and hashes cannot be ordered. If you want to display quotes by sorted author name, you could do this :

Note : Enumerable#group_by does not exist in ruby 1.8, it only exists in Rails. The method will be in ruby 1.9 however.

(3 votes, average: 5 out of 5)

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