How to retrieve a value from an object by passing a variable as a key

Question

I have the following array of objects

position = [
    {exchange: 'KRAKEN', USD: 1800, EUR: 800, GBP: 800, BTC: 800},
    {exchange: 'BTCE', USD: 800, EUR: 800, GBP: 800, BTC: 800},
    {exchange: 'BITSTAMP', USD: 600, EUR: 800, GBP: 800, BTC: 800},
    {exchange: 'MYWALLET', USD: 1300, EUR: 800, GBP: 800, BTC: 800}
]

I also have 2 variables: myExchange and myCurr

I'm attempting to extract the relevant currency value from the array. i.e. if myExchange = 'KRAKEN' and myCurr = USD,then I need to fetch the result as = 1800

I'm using the following code in coffeescript (and underscore ._ as library) but it is returning as 'undefined'

    objBuy = _.find(position, (objBuy) ->
      objBuy.exchange is buyExchange
    )

    objBuyCurr = _.find(objBuy, (objBuyCurr) ->
      objBuy._key is buyCurr
    )

Eventually what I'm aiming for is to pass the object property/keys as variables dynamically. i.e.: value = position.myExchange.myCurr (and NOT position.KRAKEN.USD)

gvlasov · Accepted Answer · 2015-02-09 15:58:48Z

1

You might want to form your data not using an array, but with a hash table (an object in JavaScript terms) which uses exchange values as keys:

position = {
    'KRAKEN': { USD: 1800, EUR: 800, GBP: 800, BTC: 800},
    'BTCE': { USD: 800, EUR: 800, GBP: 800, BTC: 800},
    'BITSTAMP': { USD: 600, EUR: 800, GBP: 800, BTC: 800},
    'MYWALLET': { USD: 1300, EUR: 800, GBP: 800, BTC: 800}
};

And then extract the required field with:

position['KRAKEN'].USD

or

position.KRAKEN.USD

In you have the name of field in a variable, for example:

var myExchange = "KRAKEN";
var myCurr = "USD";

then remember that you can access any field of an object as if it was an index of an array:

position[myExchange][myCurr];

edited Feb 9, 2015 at 15:58

answered Feb 9, 2015 at 15:44

gvlasov

20.3k22 gold badges85 silver badges120 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

saurabh goyal Over a year ago

Thanks Suseika. What I need however is to be able to say: position.myExchange.myCurr. i.e. us the variables dynamically. Is that possible at all ?

Collectives™ on Stack Overflow

How to retrieve a value from an object by passing a variable as a key

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related