a gem to add J language array commands to Ruby
Ruby
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README.rdoc

jop

DESCRIPTION:

Jop is a gem that adds operations of the J programming language to Ruby arrays.

One could legitimately ask why anyone would want to do such a thing. No one in the Ruby community has been screaming “Oh, if only I could rotate N dimensional matrices and reduce them with powerful operators from an obscure APL-derived language, I could be happy.” But, it's only a matter of time, isn't it?

FEATURES/PROBLEMS:

  • Currently supports a handful of monadic operators and a few dyads

  • Operators can be chained together but 'fork' and 'hook' are not implemented

  • Most operators assume arrays of integers or floats

  • Error handling isn't graceful

SYNOPSIS:

Imagine wanting to square an array of integers. We can do this in Jop using the '*:' operator:

[0, 1, 2].j('*:')

From this we get:

[0, 1, 4]

In typical J fashion, operators work on arrays of any dimension:

[[0, 1, 2], [3, 4, 5]].j('*:')

Here's the result:

[[0, 1, 4], [9, 16, 25]]

In Jop, J operators are applied right to left. We can do a 'take' operation to get the the first array of the squared elements of [[0, 1, 2], [3, 4, 5]] like this:

[[0, 1, 2], [3, 4, 5]].j('{.*:')

We are applying the 'take' operator '{.' after the square operator '*:' This is the result:

[0, 1, 4]

At this point, you might be wondering where we get all of these cool multi-dimensional arrays. We can create them using the Shape operator '$':

[1, 2, 3].j('3 4 $')

This expression produces:

[[1, 2, 3, 1], [2, 3, 1, 2], [3, 1, 2, 3]]

3 and 4 are the dimensions of the array we are producing. The array is filled with the values 1, 2 and 3 from the beginning and we repeat that sequence of 1s, 2s and 3s as long as there are more elements to fill.

Arrays can be of any dimension. It you really want to try this you can but it's between you and the Ruby runtime:

[42].j(12 12 12 12 12 12 12 $')

The coup de grâce is the insert operator '/'. You can use it to insert an operator between each element of an array and evaluate it. This is akin to Ruby's inject:

[1, 2, 3].j('+/')

This expression inserts '+' between 1, 2, and 3. We get:

[6]

Insertion works on multi-dimensional arrays too:

[[1, 2, 3], [4, 5, 6]].j('+/')

We get the pair-wise sum of the elements of each array

[5, 7, 9]

We can 'fold' across both dimensions like this:

[[1, 2, 3], [4, 5, 6]].j('+/+/')

That give us the total sum:

[21]

FUTURE DIRECTIONS:

  • DSL-ish operations syntax for users who don't want to use J syntax

  • Support for full J syntax using printf-style argument interpolation to supply arrays within expressions

REQUIREMENTS:

  • Ruby 2.0 and patience

INSTALL:

  • sudo gem install jop

LICENSE:

(The MIT License)

Copyright © 2013 Michael Feathers

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.