Creating a map from an array of arrays in Ruby

Question

I'm trying to write a function in Ruby which can take in a in an array of arrays, and convert it into a hash. This will be used to simulate grammar and generate random sentences. The resulting map will be helpful in generating all combination of sentences available with the current grammar rules.

The array of arrays to be input is in the following format:

[  
["<start>", "The   <object>   <verb>   tonight."],   
["<object>", "waves", "big    yellow       flowers", "slugs"],   
["<verb>", "sigh <adverb>", "portend like <object>", "die <adverb>"],   
["<adverb>", "warily", "grumpily"]  
]

After passing this into the function, and mapping it, the result should be as such:

{
"<start>"=>[ ["The", "<object>", "<verb>", "tonight."] ], 
"<object>"=>[ ["waves"] , ["big", "yellow", "flowers"] , ["slugs"] ], 
"<verb>"=>[ ["sigh", "<adverb>"] , ["portend", "like", "<object>"] , ["die", "<adverb>"] ], 
"<adverb>"=>[ ["warily"] , ["grumpily"] ]
}

For each non-terminals, it should map its corresponding productions to it. For example, will contain "warily" and "grumpily" as those two are the productions corresponding to the non-terminal .

How do I go about achieving this? I'm a bit lost as to where to start.

Welcome to SO. We'd like to see your attempt toward solving this, rather than a request for code. Please read "How to Ask" including the linked pages, "minimal reproducible example" and “How much research effort is expected of Stack Overflow users?”. Currently your question is premature; Try, try, try some more, then ask a specific question about one part of your code. — the Tin Man
– the Tin Man, Commented Oct 29, 2016 at 19:00

4 revs, 2 users 94% · Accepted Answer · 2016-10-28 23:48:52Z

2

Try this:

arr = [ ["<start>", "The   <object>   <verb>   tonight."],   
        ["<object>", "waves", "big    yellow       flowers", "slugs"],   
        ["<verb>", "sigh <adverb>", "portend like <object>", "die <adverb>"],   
        ["<adverb>", "warily", "grumpily"] ]

arr.map { |ar| [ar.shift, ar.map { |str| str.split }] }.to_h
#=>
#{ "<start>"  => [["The", "<object>", "<verb>", "tonight."]],
#  "<object>" => [["waves"], ["big", "yellow", "flowers"], ["slugs"]],
#  "<verb>"   => [["sigh", "<adverb>"], ["portend", "like", "<object>"], ["die", "<adverb>"]],
#  "<adverb>" => [["warily"], ["grumpily"]] }

ar.shift takes the first element of each subarray. The block used with ar.map splits (on whitespace) the remaining elements into arrays. Finally to_h converts the resulting array into a hash.

edited Oct 28, 2016 at 23:48

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4 revs, 2 users 94%
sagarpandya82

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5 Comments

FlameDra Over a year ago

Thanks, its working! Can you give a me a bit of an explanation of whats happening?

Ursus Over a year ago

@sagarpandya82 I updated your answer. It's better in this way for me. Check if you like it ;)

Sagar Pandya Over a year ago

@Ursus your latest update actually gave a different output, so rolled back.

souslov Over a year ago

Hash[ arr.map(&:shift).zip( arr.map{|x| x.map(&:split)}) ] also

Gopal Over a year ago

This is aGood one!

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