Re: Accessing JSON Array data in Clojure

[Michael Klishin]

2013/5/7 Hawkeye02 <bryan.d....@gmail.com>

I can't get the data from inside the JSON arrays from Clojure.  Specifically, I looking to get the data from the "currently" array taken from this Dark Sky data:

Sorry but your JSON document example does not have arrays. Do you mean nested objects (maps)?

Parsed JSON documents are returned as Clojure maps. In your example, the issue seems to be that keys in the map

you have a strings but you are trying to access them as keywords. clojure.core/get-in is what I'd use instead [3].

And please don't use clojure.contrib.* stuff. Monolithic contrib has been deprecated a couple of years ago and is no longer

maintained. Use Cheshire [1] or data.json (I don't recommend this one) [2].

Finally, take a look at http://clojure-doc.org if you need a free beginner documentation resource.

1. http://github.com/dakrone/cheshire

2. http://github.com/clojure/data.json

3. http://clojuredocs.org/clojure_core/clojure.core/get-in

--
MK

http://github.com/michaelklishin
http://twitter.com/michaelklishin

[Hawkeye02]

Michael,

Thank you for the response and references.  I will try your suggestions and get back to you.  My terminology isn't the best, thanks for deciphering.  

[greg r]

You might want to check out "Clojure Data Analysis Handbook" by Eric Rochester.  There is an example using org.clojure/data.json and Incanter to read JSON format into an Incanter dataset.  You might find other recipes in the book useful as well:

http://www.packtpub.com/clojure-data-analysis-cookbook/book

I'm going through it (slowly) and learning a lot.  It's not a beginner's book.  Full blast functional programming for sure.

Regards,
Greg

[Hawkeye02]

Thanks Greg for the suggestion.  I have added the book to my Safari account.

Michael, I tried your suggestion with 'get-in' and it came back with [object Object] from JSON.  I switched the clojure.contrib stuff with data.json.

Below is the updated code and a screenshot of the result.  Thanks in advance for any guidance.

(ns brainiac.plugins.dark-sky

  (:require [brainiac.plugin :as brainiac]

            [clojure.data.json :as json]

            [clojure.java.io :as io :only (reader)]

            [clojure.core :as core]))

(defn format-forecast [forecast]

  {

    :temp (:currentTemp forecast)

    :current-summary (:currentSummary forecast)

    :hour-summary (core/get-in :dayPrecipitation [:temp] forecast)

    :minutes-until-change (:minutesUntilChange forecast)

  })

(defn transform [stream]

  (let [json (json/read-json (io/reader stream))]

    (assoc {}

      :name "dark-sky"

      :title "Right now, outside..."

      :data (format-forecast json))))

(defn url [api-key lat lon]

  (format "https://api.darkskyapp.com/v1/forecast/%s/%s,%s" api-key lat lon))

(defn configure [{:keys [api-key lat lon program-name]}]

  (brainiac/simple-http-plugin

    {:url (url api-key lat lon)}

    transform program-name))

[Hawkeye02]

Forgot to put the JSON data:

"radarStation":"lot","dayPrecipitation":[{"time":1368129600,"probability":0.23,"type":"rain","temp":74,"cloudCover":1,"relHumidity":0.45},......

[Michael Klishin]

2013/5/10 Hawkeye02 <bryan.d....@gmail.com>

:hour-summary (core/get-in :dayPrecipitation [:temp] forecast)

I don't think you use get-in the way it is demonstrated in the examples. It takes a map

as the first argument and a collection of keys to traverse.

http://clojuredocs.org/clojure_core/clojure.core/get-in

Also, you don't need to require clojure.core. It is automatically loaded and referred to.

[Bryan Henderson]

What map would be defined for the first argument with the given code?  It seems like how it is set up, it is grabbing information straight from the JSON data without a map defined.  The 'format-forecast' definition takes forecast as an arg so I tried it like this with no luck:

:hour-summary (core/get-in forecast [:dayPrecipitation :temp])

I wasn't sure what else to put for the first argument.

Thanks for the heads up on the clojure.core requirement.  I saw it in some other code online; figured I needed it.

Also, thanks again for the help.

 

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[Michael Klishin]

2013/5/10 Bryan Henderson <bryan.d....@gmail.com>

What map would be defined for the first argument with the given code?  It seems like how it is set up, it is grabbing information straight from the JSON data without a map defined.

Parsed JSON

 

 The 'format-forecast' definition takes forecast as an arg so I tried it like this with no luck:

:hour-summary (core/get-in forecast [:dayPrecipitation :temp])

I don't know what "no luck" means exactly but you are using keywords again while your map contains

strings as keys. "time" is not the same as :time.

Here's the time of the first precipitation, in a REPL session:

https://gist.github.com/michaelklishin/2569d3e6eb32d6e8172b

[Thomas Heller]

Hey,

I only glanced over the discussion, but I think you have a type problem. Keyword vs. Strings to be precise, the JSON data you pasted will not convert to keyword keys by default I think.

So instead of (core/get-in forecast [:dayPrecipitation :temp])

try (core/get-in forecast ["dayPrecipitation" "temp"])

HTH,

/thomas