CODEWITHSUNDEEP
ruby-on-railsrubyarraysjson
adbarads
adbarads

Reputation: 1303

How to iterate through an JSON array to get a value of a key?

I have a response string that looked something like this:

"[{\"id\":\"blahbla23sdlkjrwer2345\",\"name\":\"bar\"},{\"id\":\"aselrjdsfsomething\",\"name\":\"foo\"}]"

Then I used JSON.parse(response_above):

json_parse = JSON.parse(response_above)

=>[{"id"=>"blahbla23sdlkjrwer2345", "name"=>"bar"},
 {"id"=>"aselrjdsfsomething", "name"=>"foo"}]

From here I only want the names and put them into an array. I figured out how to get the names but don't how to build it into a new array.

To get just "foo" or "bar" I can do this:

json_parse[0].fetch("name")
=> "bar"

json_parse[1].fetch("name")
=> "foo"

I don't how to iterate through the array to build a new array from the JSON response like:

new_array = ["foo", "bar"]

The JSON response can be dynamic, sometimes I may only have 2 elements, other times I can have 10 elements. I can't hard code a value in. I need to find a way to iterate through that array for the "name" key getting each of the values.

Upvotes: 1

Views: 4307

Answers (2)

Anthony
Anthony

Reputation: 15977

Like many Ruby answers there are a few ways to do it:

Setup: 

[1] pry(main)> require 'json'
=> true
[2] pry(main)> json = JSON.parse("[{\"id\":\"blahbla23sdlkjrwer2345\",\"name\":\"bar\"},{\"id\":\"aselrjdsfsomething\",\"name\":\"foo\"}]")

using #inject:

[5] pry(main)> json.inject([]) { |arr, entry| arr << entry['name'] ; arr }
=> ["bar", "foo"]

using #map as Nerian pointed out:

[6] pry(main)> json.map { |entry| entry['name'] }
=> ["bar", "foo"]

using #collect:

[7] pry(main)> json.collect { |entry| entry['name'] }
=> ["bar", "foo"]

Some interesting benchmarks on the subject as well. I created an array with a million hashes in them and called the 3 methods above on it. #collect appears to be the fastest though the tests vary a bit from run to run.

       user     system      total        real
map  0.300000   0.020000   0.320000 (  0.325673)
collect  0.260000   0.030000   0.290000 (  0.285001)
inject  0.430000   0.010000   0.440000 (  0.446080)

Upvotes: 3

Nerian
Nerian

Reputation: 16197

Here is how:

2.1.3 :006 > require 'json'
 => true 
2.1.3 :007 > json = JSON.parse("[{\"id\":\"blahbla23sdlkjrwer2345\",\"name\":\"bar\"},{\"id\":\"aselrjdsfsomething\",\"name\":\"foo\"}]")
 => [{"id"=>"blahbla23sdlkjrwer2345", "name"=>"bar"}, {"id"=>"aselrjdsfsomething", "name"=>"foo"}] 
2.1.3 :008 > json.map { |entry| entry['name'] }
 => ["bar", "foo"]

Upvotes: 6

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