Discussion on: Daily Challenge #216 - Rainfall

[kesprit]

My Swift solution, not the best ☹️:

func fetchCity(datas: String) -> [String: [Double]] {
    func fetchCityDatas(datas: String) -> [Double] {
        datas.split(separator: ",").map {
            Double($0.split(separator: .init(" ")).last ?? "") ?? 0
        }
    }

    return data.split(separator: "\n").reduce(into: [String:[Double]]()) {
        let data = $1.split(separator: ":")
        $0[String(data.first ?? "")] = fetchCityDatas(datas: String(data.last ?? ""))
    }
}

func mean(town: String, datas: String) -> Double {
    let convertedDatas = fetchCity(datas: datas)
    guard convertedDatas.contains(where: { $0.key == town }), let townDatas = convertedDatas[town] else { return -1 }

    let sum = townDatas.reduce(into: 0.0) { $0 += $1 }

    return sum / Double(townDatas.count)
}

func variance(town: String, datas: String) -> Double {
    let meanValue = mean(town: town, datas: datas)
    let convertedCities = fetchCity(datas: datas)
    guard let convertedDatas = convertedCities[town] else { return 0 }

    return convertedDatas.map { pow((meanValue - $0),2) }
        .reduce(into: 0.0) { $0 += $1 } / Double(convertedDatas.count)
}

mean(town: "Rome",datas: data1)
mean(town: "Beijing",datas: data)
variance(town: "Beijing",datas: data1)
variance(town: "Lima",datas: data)