How to extract data from a complex Javascript object?

Question

Suppose, I have a simple following code snippet of Javascript.

let data = {
    "ethusd": {
        "at": 1581416882,
        "ticker": {
            "buy": "218.87",
            "sell": "219.0",
            "low": "0.0",
            "high": "0.0",
            "open": 209.09,
            "last": "0.0",
            "volume": "72877.8789",
            "avg_price": "213.699103431748658920247612509",
            "price_change_percent": "-100.00%",
            "vol": "72877.8789"
        }
    },
    "trstusd": {
        "at": 1581416882,
        "ticker": {
            "buy": "0.0",
            "sell": "0.0",
            "low": "0.0",
            "high": "0.0",
            "open": "0.0",
            "last": "0.0",
            "volume": "0.0",
            "avg_price": "0.0",
            "price_change_percent": "+0.00%",
            "vol": "0.0"
        }
    },
    "trsteth": {
        "at": 1581416882,
        "ticker": {
            "buy": "0.0",
            "sell": "0.0",
            "low": "0.0",
            "high": "0.0",
            "open": "0.0",
            "last": "0.0",
            "volume": "0.0",
            "avg_price": "0.0",
            "price_change_percent": "+0.00%",
            "vol": "0.0"
        }
    }
}


for (let element in data)
{
	let innerElement = data[element];
	
	for (let innerData in innerElement)
	{
		if (innerData !== "at")
		{
			let internalData = innerElement[innerData];

			for (let x in internalData)
			{
				console.log(x,internalData[x]);
			}
		}
	}
}

What I tried on that above code is to get the value of buy and sell in particular. So I wrote a code in that way. Is this a good way to extract data from a javascript object or JSON data format? If not, what are the efficient ways and good practices?

stfno.me · Accepted Answer · 2020-02-12 09:42:03Z

3

It depends on what you want to do.

For example, if you have to take all the ticker of each exchange:

for(let exchange in data) {
    var ticker = data[exchange]["ticker"];
    console.log(ticker);
    // maybe here you can creare row of a table? (example)
}

or..

for(let exchange in data) {
    var ticker = data[exchange].ticker;
    console.log(ticker);
    // maybe here you can creare row of a table? (example)
}

If you want to access the ticker of a specific exchange instead:

var ticker = data["ethusd"]["ticker"];

or..
var ticker = data.ethusd["ticker"];

or..
var ticker = data.ethusd.ticker;

Obviously you have to check if the field exists:

var exist = typeof data.ethusd !== 'undefined' && data.ethusd !== null;

or..
var exist = typeof data["ethusd"] !== 'undefined' && data["ethusd"] !== null;

or..
var exist = (!!data.ethusd);

or..
var exist = (!!data["ethusd"]);

This is a simple Javascript object, you can access it through the object field or via field name as 'key' of dictionary.

edited Feb 12, 2020 at 9:42

answered Feb 12, 2020 at 9:30

stfno.me

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2 Comments

Shah Shishir Over a year ago

Thanks. But if the data is dynamic and some keys are unknown, then what is the approach to get those data?

stfno.me Over a year ago

If the data is dynamic you must iterate over fields of your object as you did. But consider that if you get this information from a Web API, you almost certainly have the field specifications. In this case, you may not have all the values of the various exchanges, but the 'ticker' object that gives you the information of 'buy' and 'sell' should remain the same. If not, your data source wasn't done very well in my opinion. Consider that if some keys are unknown, you will never be able to access them, you should put a new condition every time you find new ones.

Tarik1322 · Accepted Answer · 2020-02-12 10:44:42Z

2

let data = {
    "ethusd": {
        "at": 1581416882,
        "ticker": {
            "buy": "218.87",
            "sell": "219.0",
            "low": "0.0",
            "high": "0.0",
            "open": 209.09,
            "last": "0.0",
            "volume": "72877.8789",
            "avg_price": "213.699103431748658920247612509",
            "price_change_percent": "-100.00%",
            "vol": "72877.8789"
        }
    },
    "trstusd": {
        "at": 1581416882,
        "ticker": {
            "buy": "0.0",
            "sell": "0.0",
            "low": "0.0",
            "high": "0.0",
            "open": "0.0",
            "last": "0.0",
            "volume": "0.0",
            "avg_price": "0.0",
            "price_change_percent": "+0.00%",
            "vol": "0.0"
        }
    },
    "trsteth": {
        "at": 1581416882,
        "ticker": {
            "buy": "0.0",
            "sell": "0.0",
            "low": "0.0",
            "high": "0.0",
            "open": "0.0",
            "last": "0.0",
            "volume": "0.0",
            "avg_price": "0.0",
            "price_change_percent": "+0.00%",
            "vol": "0.0"
        }
    }
}

let valueOfKeysToFound = ['buy', 'sell'];
let simpleObjSubset = [];

function scrapData(obj, valueOfKeysToFound) {
    if (typeof obj === 'object') {
        let tempValues = {};
        let keyFoundCount = 0;

        for (let property in obj) {
            let value = obj[property];

            if (typeof value === 'object') {
                scrapData(value, valueOfKeysToFound);
            } else if (valueOfKeysToFound.includes(property)) {
                tempValues[property] = value;
                keyFoundCount++;

                if (keyFoundCount == valueOfKeysToFound.length) {
                    simpleObjSubset.push(tempValues);
                    break;
                }
            }
        }
    } 
}

scrapData(data, valueOfKeysToFound);
console.table(simpleObjSubset);

When one say efficient it means robust enough from performance perspective and when one say good practice it is ambiguous from person to person, problem to problem and logic to logic.

The problem you mentioned can be solved by approach I wrote, why I solve it this way? Because

I know what each line does.
It is flexible to scale.
It can check N number of depth.

And most important part whatever you write as a solution must give you enough control to change anything.

answered Feb 12, 2020 at 10:44

Tarik1322

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3 Comments

stfno.me Over a year ago

I know your code snippet is an example. But considering that @Shah Shishir said that his object is dynamic, that snippet of code find all 'buy' and 'sell' fields at different points of the object. This could cause an incorrect reading of the object.

Tarik1322 Over a year ago

I agree, this code snippet could be a base for him to make flexible changes. Not exact solution.

Tarik1322 Over a year ago

Also, if for example 'buy' and 'sell' are in different hierarchy then he needs to form output the way he wants. Solution I proposed gets buy and sell from same level of object hierarchy, so I have given a gum which can be molded as per the expected outcome.

noamyg · Accepted Answer · 2020-02-12 11:36:23Z

1

As far as readability goes, I'd go with lodash.

If you know the path of that buy and sell keys you're looking for, you can use ._get, i.e.:
```
_.get(data, 'ethusd.ticker.buy')
_.get(data, 'trstusd.ticker.sell')
```
If you do not know the exact path, you can use _.findKey

Regarding efficiency, manual deconstruction would probably be faster as demonstrated here, but we're talking about millions of executions per second on both scenarios... I'm going with readability, once again. :-)

edited Feb 12, 2020 at 11:36

answered Feb 12, 2020 at 11:20

noamyg

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