rails + activerecord: how create a hash from table with particular field's value as key

Question

Given a table ZipCodeInfos with fields zipcode, state, city (all strings), where zipcode is unique:

zipcode,city,state
"10000", "Fooville", "AA"
"10001", "Smallville", "AA"
"10002", "Whoville", "BB"

What is the fastest way to generate a hash object of the entire table where the zipcode is a key like this:

{ "10000" => {:city => "Fooville", :state => "AA" },
"10001" => {:city => "Smallville", :state => "AA" },
"10002" => {:city => "Whoville", :state => "BB" } }

I know for a given record I can use .attributes to generate a hash with key,value pairs of field-names, field-values, for example Zipcode.first.attributes gives me

{"id" => 1, "zipcode" => "10000", "city" => "Fooville", "state => "AA" }

But, short of brute force iterating over each record (via .map), I cannot quite figure out how to create the desired hash with the zipcode as the key for each node of the hash.

This is the best I could come up with, and I suspect there is some nifty Ruby goodness that is faster?

zip_info_hash = {}
ZipCodeInfo.all.map{|x| zip_info_hash[x.zip] = 
                       {'state' => x.state, 'city' => x.city }}

Sebastián Palma · Accepted Answer · 2017-12-04 16:41:30Z

3

You could also try:

ZipCodeInfos.all.group_by &:zipcode

will get you a hash of zip code to array of ZipCodeInfos activerecords.

edited Dec 4, 2017 at 16:41

Sebastián Palma

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answered May 11, 2016 at 21:02

Tom

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Comments

Ajay Barot · Accepted Answer · 2017-08-03 18:05:10Z

1

You can use inject method. Here is what I generally use.

def visitors_name_email
  visitors.inject({}) do |result, visitor|
    result.merge(visitor.name => visitor.email)
  end
end

edited Aug 3, 2017 at 18:05

Ajay Barot

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answered Jan 20, 2014 at 19:55

Addicted

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Comments

Beder Acosta Borges · Accepted Answer · 2014-05-15 14:04:20Z

0

I can't think of a way to avoid map here. I'd make only some minor changes to your code:

zip_info=Hash[*ZipCodeInfo.all
                          .map{|x| [x.zip, {:city => x.city, :state => x.state}]}
                          .flatten]

edited May 15, 2014 at 14:04

answered May 15, 2014 at 10:56

Beder Acosta Borges

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