Duplo

A tiny Ruby DSL for generating collections.

Let's say you like matrices (bear with me) but not rolling them out by hand. Or say you need to generate some data samples quickly in the console but writing nested loops is not really your idea of fun.

So how about this:

require "duplo"
include Duplo

a4a8
#=> [[0, 1, 2, 3, 4, 5, 6, 7],
#    [0, 1, 2, 3, 4, 5, 6, 7],
#    [0, 1, 2, 3, 4, 5, 6, 7],
#    [0, 1, 2, 3, 4, 5, 6, 7]]

Bam. A 4x8 matrix.

Want it randomized? Just pass it a block to populate the entries:

a4a8 { rand 10 }
#=> [[5, 1, 2, 7, 8, 9, 6, 1],
#    [7, 6, 6, 0, 7, 1, 0, 8],
#    [9, 3, 8, 7, 6, 4, 4, 5],
#    [3, 0, 9, 0, 7, 3, 8, 9]]

This works too:

Duplo.a4a8

so including the module is optional. The gem works its magic through method_missing so it won't stomp on existing names either way.

Populating the entries is easy peasy. Here, have an identity matrix:

I5 = a5a5 { |i, j| i == j ? 1 : 0 }
#=> [[1, 0, 0, 0, 0],
#    [0, 1, 0, 0, 0],
#    [0, 0, 1, 0, 0],
#    [0, 0, 0, 1, 0],
#    [0, 0, 0, 0, 1]

If plain old matrices bore you, you can do simple vectors:

a10 { |i| i ** 2 }
#=> [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

or arbitrary tensors:

a4a11a2a3 { |path| path.join(":") }
#=> [[[["0:0:0:0", "0:0:0:1", "0:0:0:2"],
#      ["0:0:1:0", "0:0:1:1", "0:0:1:2"]],
#      . . .
#      ["3:10:1:0", "3:10:1:1", "3:10:1:2"]]]]

The last example also shows how to use the full entry path without destructuring.

In addition to arrays, you can build hashes and sets, and mix and match collection types to your heart's desire:

sa2h3 { rand 100 }
#=> #<Set: {[{0=>11, 1=>47, 2=>48}, {0=>3,  1=>71, 2=>57}],
#           [{0=>97, 1=>9,  2=>43}, {0=>90, 1=>30, 2=>62}],
#           [{0=>87, 1=>56, 2=>23}, {0=>24, 1=>16, 2=>63}],
#           [{0=>6,  1=>12, 2=>57}, {0=>44, 1=>3,  2=>74}],
#           [{0=>52, 1=>92, 2=>12}, {0=>93, 1=>32, 2=>1}]}>

Let's spell that out:

Duplo.spell "sa2h3"
#=> "5-element Set containing 2-element Arrays containing 3-element Hashes"

Note that I've omitted size for the root collection there. It defaults to 5, so aaa yields the same result as a5a5a5. Set your preferred default like this:

Duplo.default_size = 10

If you want to supply dimensions dynamically, this should do the trick:

m, n = 3, 4
toy = "a#{m}a#{n}"

Duplo.build(toy) { rand }

Add this line to your application's Gemfile:

gem "duplo"

or install it yourself as:

$ gem install duplo

My personal preference is to drop this into .irbrc (or .pryrc):

require "duplo"
include Duplo

and have all those handy shortcuts available in every session.

To test the gem, clone the repo and run:

$ bundle && bundle exec rake

This gem is released under the MIT License.