Ruby: Extract elements from deeply nested JSON structure based on criteria

Question

Want to extract every marketID from every market that has a marketName == 'Moneyline'. Tried a few combinations of .maps, .rejects, and/or .selects but can't narrow it down as the complicated structure is confusing me.

There are many markets in events, and there are many events as well. A sample of the structure (tried to edit it for brevity):

{"currencyCode"=>"GBP",
"eventTypes"=>[
    {"eventTypeId"=>6423,
    "eventNodes"=>[
        {"eventId"=>28017227,
        "event"=>
            {"eventName"=>"Philadelphia @ Seattle"
            },
            "marketNodes"=>[
                {"marketId"=>"1.128274650",
                "description"=>
                    {"marketName"=>"Moneyline"}
                },
                {"marketId"=>"1.128274625",
                "description"=>
                    {"marketName"=>"Winning Margin"}
                }}}]},
        {"eventId"=>28018251,
        "event"=>
            {"eventName"=>"Arkansas @ Mississippi State"
            },
            "marketNodes"=>[
                {"marketId"=>"1.128299882",
                "description"=>
                    {"marketName"=>"Under/Over 60.5pts"}
                },
                {"marketId"=>"1.128299881",
                "description"=>
                    {"marketName"=>"Moneyline"}
                }}}]},
        {"eventId"=> etc....

Tried all kinds of things, for example,

markets = json["eventTypes"].first["eventNodes"].map {|e| e["marketNodes"].map { |e| e["marketId"] } if (e["marketNodes"].map {|e| e["marketName"] == 'Moneyline'})}
markets.flatten
# => yields every marketId not every marketId with marketName of 'Moneyline'

Getting a simple array with every marketId from Moneyline markets with no other information is sufficient. Using Rails methods is fine too if preferred.

Sorry if my editing messed up the syntax. Here's the source. It looks like this only with => instead of : after parsing the JSON.

Thank you!

rather not use outside resources. this is in a rails app so either ruby or rails methods — iamse7en
– iamse7en, Commented Nov 19, 2016 at 22:28
@EricDuminil Sorry if my editing messed it up. See here: betfair.com/www/sports/exchange/readonly/v1/… In my console, it basically looks exactly like that only with => instead of : after parsing. It's a little messy. — iamse7en
– iamse7en, Commented Nov 19, 2016 at 22:38

Eric Duminil · Accepted Answer · 2016-11-19 22:56:26Z

2

I love nested maps and selects :D

require 'json'

hash = JSON.parse(File.read('data.json'))

moneyline_market_ids = hash["eventTypes"].map{|type|
  type["eventNodes"].map{|node|
    node["marketNodes"].select{|market|
      market["description"]["marketName"] == 'Moneyline'
    }.map{|market| market["marketId"]}
  }
}.flatten

puts moneyline_market_ids.join(', ')
#=> 1.128255531, 1.128272164, 1.128255516, 1.128272159, 1.128278718, 1.128272176, 1.128272174, 1.128272169, 1.128272148, 1.128272146, 1.128255464, 1.128255448, 1.128272157, 1.128272155, 1.128255499, 1.128272153, 1.128255484, 1.128272150, 1.128255748, 1.128272185, 1.128278720, 1.128272183, 1.128272178, 1.128255729, 1.128360712, 1.128255371, 1.128255433, 1.128255418, 1.128255403, 1.128255387

answered Nov 19, 2016 at 22:56

Eric Duminil

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4 Comments

iamse7en Over a year ago

yowza. perfect. Thank you kindly! My head was hurting trying to figure it out.

iamse7en Over a year ago

Hey @eric-duminil, if you have a minute to spare, I have a more challenging brain teaser here. Source: betfair.com/www/sports/exchange/readonly/v1/…. I want to select marketIds == 'Moneyline' but only those with countryCode == 'US' || 'GB' OR eventName.include?(' @ '). (space before and after the @). I tried different combos of map and select but some nodes don't have 'countryCode` which complicates things. There is some overlap with those last two criteria, so uniq may be necessry? TIA!

Eric Duminil Over a year ago

Please write another question.

iamse7en Over a year ago

Right! stackoverflow.com/questions/40708340/…. Really do appreciate it!

Eric Duminil · Accepted Answer · 2016-11-19 23:08:41Z

Just for fun, here's another possible answer, this time with regexen. It is shorter but might break depending on your input data. It reads the json data directly as String :

json = File.read('data.json')

market_ids   = json.scan(/(?<="marketId":")[\d\.]+/)
market_names = json.scan(/(?<="marketName":")[^"]+/)

moneyline_market_ids = market_ids.zip(market_names).select{|id,name| name=="Moneyline"}.map{|id,_| id}
puts moneyline_market_ids.join(', ')
#=> 1.128255531, 1.128272164, 1.128255516, 1.128272159, 1.128278718, 1.128272176, 1.128272174, 1.128272169, 1.128272148, 1.128272146, 1.128255464, 1.128255448, 1.128272157, 1.128272155, 1.128255499, 1.128272153, 1.128255484, 1.128272150, 1.128255748, 1.128272185, 1.128278720, 1.128272183, 1.128272178, 1.128255729, 1.128360712, 1.128255371, 1.128255433, 1.128255418, 1.128255403, 1.128255387

It outputs the same result as the other answer.

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