您可以尝试这种方法，使用动态键，在我的测试工作：

struct ResponseAPI: Decodable {
    var ts: [Int]
    var units: [String:String]
    var data: [String:[Float]]

    init(ts: [Int], units: [String:String], data: [String:[Float]]) {
       self.ts = ts
       self.units = units
       self.data = data
    }
    
    enum CodingKeys: String, CodingKey {
        case ts, units
    }
    
    struct AnyKey: CodingKey {
        var stringValue: String
        var intValue: Int?
        
        init?(stringValue: String) {  self.stringValue = stringValue  }
        init?(intValue: Int) { return nil } // never used
    }
    
    init(from decoder: Decoder) throws {
        let container1 = try decoder.container(keyedBy: CodingKeys.self)
        self.ts = try container1.decode([Int].self, forKey: .ts)
        self.units = try container1.decode([String:String].self, forKey: .units)
        self.data = [:]
        let container2 = try decoder.container(keyedBy: AnyKey.self)
        container2.allKeys.forEach { key in
            if let theFloats = try? container2.decode([Float].self, forKey: key) {
                self.data[key.stringValue] = theFloats
            }
        }
    }
    
}