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AS guide: documents Enumerable#group_by

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1 parent b4e11df commit e0d3cec3cc4c0e8baa2440202f9451a35b3ef9d5 @fxn fxn committed Sep 15, 2009
Showing with 13 additions and 1 deletion.
  1. +13 −1 railties/guides/source/active_support_overview.textile
@@ -788,7 +788,19 @@ h3. Extensions to +BigDecimal+
h3. Extensions to +Enumerable+
-...
+h4. +group_by+
+
+Ruby 1.8.7 and up define +group_by+, and Active Support does it for previous versions.
+
+This iterator takes a block and builds an ordered hash with its return values as keys. Each key is mapped to the array of elements for which the block returned that value:
+
+<ruby>
+entries_by_surname_initial = address_book.group_by do |entry|
+ entry.surname[0, 1].upcase
+end
+</ruby>
+
+WARNING. Active Support redefines +group_by+ in Ruby 1.8.7 so that it still returns an ordered hash.
h3. Extensions to +Array+

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