most efficient ruby way to transform this array?

Question

I have an array in the following form:

  [\"id\", 545, \"program_name\", \"VILLIANS MARATHON\", \"episode_name\", \"1-Season1:Ep.11\"]

I need to transform it to the form below:

  [545, \"VILLIANS MARATHON\", \"1-Season1:Ep.11\"]

The way Im doing this is as follows:

    #Convert a Active record hash to a 2D array
def activerecord_hash_to_datatable_array(activerecord_resultset)
array_of_arrays = Array.new()
array_of_rs_hashes = activerecord_resultset.to_a.map(&:serializable_hash)

array_of_rs_hashes.each do |rs| 
# {"id"=>1594, "program_name"=>nil, "episode_name"=>nil}
rs =  rs.flatten
#[\"id\", 545, \"program_name\", \"MARATHON\", \"episode_name\", \"1-Season1:Ep.11\"]"
rs_array = Array.new()
index = 1
while index < rs.length     
    puts "index = #{index}"     
    puts "\033[0;33m"+"#{rs[index]}"+"\033[0;37m"
    log_with_yellow("index[#{index}] " + "#{rs[index]}")
    rs_array << rs[index]
    index += 2
end
array_of_arrays <<  rs_array
end
array_of_arrays
end

I was wondering what the most efficient way to accomplish this is.

Clearly I need to retain only odd elements. But Id like to avoid iterating over all elements and comparing each elements index.

Is there a way to do this by skipping all the even elements ?

Thanks

this is no 2D array but a single array, looks like a JSON object stored in an array — bjhaid
– bjhaid, Commented Jan 15, 2014 at 16:34
@BroiSatse its a JSON object, check my answer and you would understand — bjhaid
– bjhaid, Commented Jan 15, 2014 at 16:43

Pierre-Louis Gottfrois · Accepted Answer · 2014-01-15 16:41:50Z

3

You can do the following:

your_array.values_at(*your_array.each_index.select(&:odd?))
=> [545, "VILLIANS MARATHON", "1-Season1:Ep.11"]

answered Jan 15, 2014 at 16:41

Pierre-Louis Gottfrois

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Comments

bjhaid · Accepted Answer · 2014-01-15 16:40:14Z

2

require 'json'
arr = JSON.parse("[\"id\", 545, \"program_name\", \"VILLIANS MARATHON\", \"episode_name\", \"1-Season1:Ep.11\"]")
new_arr = arr.select.with_index { |x,i| i.odd? }
p new_arr
# >> [545, "VILLIANS MARATHON", "1-Season1:Ep.11"]

answered Jan 15, 2014 at 16:40

bjhaid

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1 Comment

Sam Over a year ago

I think this is the correct way to do it. Since it's a json, your given array isn't really an array due to the '\'s. So you would need to JSONify them to make a valid array, on which you can then perform select.

steenslag · Accepted Answer · 2014-01-15 17:00:57Z

1

If array_of_rs_hashes is indeed an array of hashes, can't you just do:

res = array_of_rs_hashes.map(&:values)

answered Jan 15, 2014 at 17:00

steenslag

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Comments

aherve · Accepted Answer · 2014-01-15 17:05:53Z

1

Yep there is :

require 'json'
Hash[*JSON.parse(s)].values #=> [545, "VILLIANS MARATHON", "1-Season1:Ep.11"]

where s = "[\"id\", 545, \"program_name\", \"VILLIANS MARATHON\", \"episode_name\", \"1-Season1:Ep.11\"]"

answered Jan 15, 2014 at 17:05

aherve

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Comments

BroiSatse · Accepted Answer · 2014-01-15 16:44:23Z

0

Try:

your_2d_array.map {|a| a.each_slice(2).map {|key, value| value}}

If you ahve active support, you can write it slightly more readible:

your_2d_array.map {|a| a.each_slice(2).map(&:second)}

edited Jan 15, 2014 at 16:44

answered Jan 15, 2014 at 16:38

BroiSatse

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1 Comment

banditKing Over a year ago

But I dont want to put magic numbers in my code. Id like the code to be extendible. This wont work if used on arrays where length is bigger than 6 !

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