Parsing a JSON object to get column data

Question

Say I have data in a JSON object formatted similar to...

{"data":
       [["X","Y","Z"], 
       ["52","23","10"],
       ["46","65","32"]]
}

So essentially, each row takes the form [X, Y, Z].

What would be the easiest way to then access an entire "column" or vector of data? For example, let's assume the "X", "Y", and "Z" is a header row, and I want to access all of the "X" data.

Do I need to iterate over the entire object somehow to retrieve the first member of each element, which would correspond to the "X" column?

I'd like to do this in JavaScript if possible.

Thanks much for any assistance!

Can you add description in which language you want to do this — Pratik Butani
– Pratik Butani, Commented Dec 10, 2014 at 6:43
@ツPratikButaniツ yep, sorry about that, added to description! :) Thank you! — JoshG
– JoshG, Commented Dec 10, 2014 at 7:35

Braj · Accepted Answer · 2014-12-10 13:38:00Z

2

Try below sample code that is simple and straight forward to access the first column.

First iterate the first row to find the correct column then get the values of that column for next rows.

<script type="text/javascript">
    var obj = {
        "data" : [ 
                   [ "X", "Y", "Z" ], 
                   [ "52", "23", "10" ],
                   [ "46", "65", "32" ] 
                 ]
    };
    var column;
    for (var i = 0, j = obj.data.length; i < j; i++) {
        if (obj.data[0][i] === 'X') {
            column = i;
            break;
        }
    }

    for (var i = 1, j = obj.data.length; i < j; i++) {
        var val = obj.data[i][column];
        console.log(val);
    }
</script>

edited Dec 10, 2014 at 13:38

answered Dec 10, 2014 at 8:09

Braj

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2 Comments

Braj Over a year ago

I am also just learing JavaScript. :)

JoshG Over a year ago

Had to make one minor fix. For the second for loop, j = obj.data.length, not obj.data[0].length. obj.data[0].length gives the length of the "variables array", so in this example, 3. obj.data.length gives the length of the data column. Submitted the edit for review. Otherwise, all good -- thanks again!

syllabus · Accepted Answer · 2014-12-10 07:11:23Z

1

"jsonpath" seems to be a good option too:

that would lead to something like

vector X: /data[1][*][1]
vector Y: /data[1][*][2]
vector Z: /data[1][*][3]

edited Dec 10, 2014 at 7:11

answered Dec 10, 2014 at 6:46

syllabus

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1 Comment

Alberto De Caro Over a year ago

Good hint. Please remember that in Stackoverflow bare links are not as much appreciated as much as links + a snippet of code applied to the question's context. If you want to suggest a link, use a comment instead of an answer.

Pratik Butani · Accepted Answer · 2014-12-10 08:16:43Z

I have run this code for Android You may tried out in JavaScript with this type of logic:

    String json = "{\"data\":[[\"X\",\"Y\",\"Z\"],[\"52\",\"23\",\"10\"],[\"46\",\"65\",\"32\"]]}";
    try {
        JSONObject jsonObj = new JSONObject(json);

        Log.i(TAG, "DatA : " + jsonObj.getJSONArray("data").length());
        JSONArray array = jsonObj.getJSONArray("data");
        for(int i=0; i<array.length(); i++) {
            Log.i(TAG, "Value : " + array.getJSONArray(i).getString(0));
        }

    } catch (JSONException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }

Output in Logcat:

12-10 12:26:32.628: I/Demo(28709): DatA : 3
12-10 12:26:32.629: I/Demo(28709): Value : X
12-10 12:26:32.629: I/Demo(28709): Value : 52
12-10 12:26:32.629: I/Demo(28709): Value : 46

Edited: For JavaScript:

<html>
<body>
<p id="demo"></p>

<script>
var text = '{\"data\":[[\"X\",\"Y\",\"Z\"],[\"52\",\"23\",\"10\"],[\"46\",\"65\",\"32\"]]}';
var out = "";
obj = JSON.parse(text);

arr = obj.data;
console.log(arr);
for(i = 0; i < arr.length; i++) {
        out += arr[i][0] + "<br>";
}

document.getElementById("demo").innerHTML = out;

</script>

</body>
</html>

blad · Accepted Answer · 2014-12-10 06:41:22Z

0

You should try using something like Gson or Jackson Json Processor to handle the JSON and deserialize it into something you can use.

One you do so, you will be able to do something like:

JsonObject json = new JsonParser().parse("...json string...");
JsonArray data = json.get("data");
JsonArray labels = data.getAsJsonArray(0)
for (int i = 1; i < data.size(); i++) {
    JsonArray points = data.getAsJsonArray(i);
    // do something with:  points.getInt(0) -- x column
    // do something with:  points.getInt(1) -- y column
    // do something with:  points.getInt(2) -- z column
}

answered Dec 10, 2014 at 6:41

blad

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