ansaurus

Question

Answer 1

+1 A:

h = Hash.new {|h, k| h[k] = []}
products.each {|p| h[p.category] << p}

Martin DeMello 2009-09-10 14:37:03

Answer 2

+4 A:

In 1.8.7+ or with active_support (or facets, I think), you can use group_by:

products.group_by {|prod| prod.category}

sepp2k 2009-09-10 14:39:28

Answer 3

A:

# a for all
# p for product
new_array = products.inject({}) {|a,p| a[p.category.name] ||= []; a[p.category.name] << p}

Eimantas 2009-09-10 14:41:19

You're missing ";a" from the end of your inject block -- the block has to return the memo hash.

glenn jackman 2009-09-10 19:30:17

thanks for the note! but doesn't last expression return the hash?

Eimantas 2009-09-11 07:01:11

No, it returns the a[p.category.name] array (the result of the Array#<< method)

glenn jackman 2009-09-11 10:34:38

A slightly shorter version using inject: products.inject(Hash.new([])) {a[p.category.name] += [p]; a}

glenn jackman 2009-09-11 10:39:26

Answer 4

A:

The oneliner

arr = [["apple", "granny"],["apple", "smith"], ["banana", "chiq"]]
h = arr.inject(Hash.new {|h,k| h[k]=[]}) {|ha,(cat,name)| ha[cat] << name; ha}

:-)

But I agree, #group_by is much more elegant.

Robert Klemme 2009-09-11 15:06:57

Reorganizing Ruby array into hash