let dict: [Int: [String: String]] = [1546696330: ["symbol": "ETH", "amount": "1.0"],
                                             1546531017: ["symbol": "ETH", "amount": "1.0"],
                                             1546531031: ["symbol": "XRP", "amount": "200.0"]]

        var toKeep: [String: Int] = [:]
        dict.forEach({
            let subDict = $0.value
            if let symbol = subDict["symbol"] {
                if let currentSaved = toKeep[symbol] {
                    toKeep[symbol] =  currentSaved > $0.key ? $0.key : currentSaved
                } else {
                    toKeep[symbol] = $0.key
                }
            }
        })

        print("ToKeep: \(toKeep)")

        var finalDict: [Int: [String: String]] = [:]
        toKeep.forEach({ finalDict[$0.value] = dict[$0.value] })
        print("finalDict: \(finalDict)")