I recently had to solve a one-off problem for work, and the solution I

came up with was about as non-DRY as you can imagine. I couldn’t

figure out how to make it simple, however. In order to expand my

knowledge, I’m hoping to get some ideas (or even related problem

domains) to solve this generically.

The problem was this:

This website has a menu of industries, a menu of categories, and a

menu of products.

If a single industry is selected, highlight the categories and

products are available for that industry.

If a single category is selected, highlight the industries and

products are available for that category.

If a single product is selected, highlight the industries and

categories available for that industry.

If a pair of items is selected (for example, one industry and one

product) show all the related items that match the intersection (for

example, all the categories that apply to the intersection of those

two choices).

I solved it by storing the data as a series of nested hashes, dictated

an order in which axes were specified, and hard-coded it for the 3

axes above, and repeated almost the same code for all 6 possible axis

queries (axis1, axis2, axis3, axis1+axis2, axis1+axis3, axis2+axis3).

It was huge and bloated and menial.

SO…this is like a data cube (in this particular set of 3

dimensions). I’m looking for a solution that is generic to n

dimensions. Doing that will simultaneously make the code simpler and

more generally useful.

Here’s Ruby code and plenty of test cases to exactly describe what I’m

looking for. It’s echoed at http://pastie.caboo.se/130061 for easier

reading and preventing unintended line-wrapping.

My preemptive thanks to all who provide some ideas (or working code)

towards the solution.

# BOYv NUM>| one | two | three |

# ----------±----------±----------±---------+

# jim | alpha | | beta |

# jam | beta | alpha | |

# jem | delta | | delta |

# jom |beta, alpha| omega | delta |

AXES = [ :boy, :num, :greek ]

COMBOS = {

:jim => {

:one => [ :alpha ],

:three => [ :beta ]

},

:jam => {

:one => [ :beta ],

:two => [ :alpha ]

},

:jem => {

:one => [ :delta ],

:three => [ :delta ]

},

:jom => {

:one => [ :beta, :alpha ],

:two => [ :omega ],

:three => [ :delta ]

}

}

def make_database( axes, nested_hash )

# Parse however you like to create

# your own data structure.

end

def fetch_options( database, axes_values = {} )

# Return all valid possibilities based on the supplied values

end

require ‘test/unit’

class TestMultiDimensionalDB < Test::Unit::TestCase

def setup

$db = make_database( AXES, COMBOS )

end

def test_one_axis

opts = fetch_options( $db, :greek=>:omega )

assert( opts[:boy] == [:jom],

“The only boy with greek:omega is jom.” )

assert( opts[:num] == [:two],

“The only num with greek:omega is two.” )

```
opts = fetch_options( $db, :greek=>:alpha )
assert( opts[:boy].length == 3,
"There are 3 boys with greek:alpha." )
assert( opts[:boy].include?(:jim),
"One of the 3 boys with greek:alpha is jim." )
assert( opts[:boy].include?(:jam),
"One of the 3 boys with greek:alpha is jam." )
assert( opts[:boy].include?(:jom),
"One of the 3 boys with greek:alpha is jom." )
assert( opts[:num].length == 2,
"There are 2 nums with greek:alpha." )
assert( opts[:num].include?(:one) && opts[:num].include?(:two),
"The nums with greek:alpha are one and two." )
opts = fetch_options( $db, :boy=>:jem )
assert( opts[:num].length == 2,
"There are 2 nums with the boy:jem." )
assert( opts[:num].include?(:one) && opts[:num].include?(:three),
"The nums with the boy:jem are one and three." )
assert( opts[:greek] == [:delta]
"The only greek with the boy:jem is delta" )
opts = fetch_options( $db, :num=>:one )
assert( opts[:boy].length == 4,
"There are 4 boys with num:one." )
assert( opts[:boy].include?(:jim),
"One of the 4 boys with num:one is jim." )
assert( opts[:boy].include?(:jam),
"One of the 4 boys with num:one is jam." )
assert( opts[:boy].include?(:jem),
"One of the 4 boys with num:one is jem." )
assert( opts[:boy].include?(:jom),
"One of the 4 boys with num:one is jom." )
assert( opts[:greek].length == 3,
"There are 3 greek with num:one." )
assert( opts[:greek].include?(:alpha),
"One of the 3 greeks with num:one is alpha." )
assert( opts[:greek].include?(:beta),
"One of the 3 greeks with num:one is beta." )
assert( opts[:greek].include?(:delta),
"One of the 3 greeks with num:one is delta." )
```

end

def test_two_axes

opts = fetch_options( $db, :greek=>:alpha, :num=>:one )

assert( opts[:boy].length == 2,

“There are 2 boys with greek:alpha and num:one.” )

assert( opts[:boy].include?(:jim) && opts[:boy].include?(:jom),

“The boys with greek:alpha and num:one are jim and jom.” )

```
opts = fetch_options( $db, :greek=>:alpha, :num=>:two )
assert( opts[:boy] == [:jam],
"The only boy with greek:alpha and num:two is jam." )
opts = fetch_options( $db, :boy=>:jom, :num=>:one )
assert( opts[:greek].length == 2,
"There are 2 greeks with the boy:jom and num:one." )
assert( opts[:greek].include?(:alpha) && opts[:greek].include?
```

(:beta),

“The greeks with the boy:jom and num:one are alpha and beta.” )

```
opts = fetch_options( $db, :boy=>:jam, :greek=>:omega )
assert( opts[:num].length == 0,
"There are no nums with the boy:jam and greek:omega." )
opts = fetch_options( $db, :boy=>:jem, :greek=>:delta )
assert( opts[:num].length == 2,
"There are 2 nums with the boy:jem and greek:delta." )
assert( opts[:num].include?(:one) && opts[:num].include?(:three),
"The nums with the boy:jem and greek:delta are one and three." )
```

end

end