CODEWITHSUNDEEP
javascriptlodash
Denys Rybkin
Denys Rybkin

Reputation: 787

Extract property from an array of objects and create another one based on this property via lodash?

I have the following array:

[
  {
    baseAsset: 'XRP',
    quoteAsset: 'ETH',
    quoteAssetPrecision: 6,
    baseAssetPrecision: 8,
    price: '0.00025170'
  },
  {
    baseAsset: 'MOD',
    quoteAsset: 'BTC',
    quoteAssetPrecision: 8,
    baseAssetPrecision: 4,
    price: '0.00004280'
  },
  {
    baseAsset: 'MOD',
    quoteAsset: 'ETH',
    quoteAssetPrecision: 8,
    baseAssetPrecision: 4,
    price: '0.00116700'
  },
  {
    baseAsset: 'ENJ',
    quoteAsset: 'BTC',
    quoteAssetPrecision: 8,
    baseAssetPrecision: 8,
    price: '0.00004508'
  },
  {
    baseAsset: 'ENJ',
    quoteAsset: 'ETH',
    quoteAssetPrecision: 6,
    baseAssetPrecision: 8,
    price: '0.00064370'
  },
  {
    baseAsset: 'STORJ',
    quoteAsset: 'BTC',
    quoteAssetPrecision: 8,
    baseAssetPrecision: 8,
    price: '0.00002090'
  },
  {
    baseAsset: 'STORJ',
    quoteAsset: 'ETH',
    quoteAssetPrecision: 6,
    baseAssetPrecision: 8,
    price: '0.00029910'
  }
]

What I want to get:

[
  {
    ticker: 'XRP',
    precision: 8,
  },
  {
    ticker: 'MOD',
    precision: 4,
  },
  {
    ticker: 'BTC',
    precision: 8,
  },
  {
    ticker: 'ENJ',
    precision: 8,
  },
  {
    ticker: 'STORJ',
    precision: 8,
  },
  {
    ticker: 'ETH',
    precision: 6,
  }
]

As you can see, each precision prop is associated with an asset and isn't changed. I want to extract each currency and its precision from my array of currency pairs. What an elegant solution can be provided via lodash? Other options are accepted. I was trying to implement this using native javascript, but solution didn't satisfied me:

const currenciesFetched = tradingPairsWithPrices
                .flatMap((pair) => [
                    {
                        ticker: pair.baseAsset,
                        precision: pair.baseAssetPrecision,
                    },
                    {
                        ticker: pair.quoteAsset,
                        precision: pair.quoteAssetPrecision,
                    },
                ])
                .filter((v, i, a) => {
                    return a.findIndex((t) => t.ticker === v.ticker) === i
                })

Any ideas?

Upvotes: 0

Views: 65

Answers (1)

skyboyer
skyboyer

Reputation: 23705

So if the goal to get uniq combination of ticker + precision and we don't expect(so don't handle) the cases when there are different precision for the same ticker, then I think the easiest way just to use native {} as a collector(or Set as more specified alternative):

const accumulator = {};
tradingPairsWithPrices.forEach(pair => {
  accumulator[pair.baseAsset] = pair.baseAssetPrecision;
  accumulator[pair.quoteAsset] = pair.quoteAssetPrecision;
});
return accumulator
  .entries()
  .map(([ticker, precision]) => ({ ticker, precision }));

It's still possible to achieve this with lodash:

_.chain(traidingPairsWithPrices)
  .flatMap(splitBaseAndQuote) // as you already do
  .uniqBy('ticker')
  .value()

If you have a long long list with a lot of entries per each ticker value then first approach will be somehow faster. But probably, not that significantly.

Upvotes: 1

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