我是熊猫新手。
我有一个数据框，我想按用户分组，然后在其速度列中找到直到该日期的最低分数。
所以我不能只使用df.groupby(['user'])['speed'].transform('min)，因为这将给出所有值的最小值，而不仅仅是从当前行到第一行。
我可以用什么来获得所需的东西？
答案 0 :(得分：0)
没有看到您的数据集，很难直接帮助您。问题确实可以归结为以下内容。您需要选择要使用的数据范围（因此，请为日期范围选择行，为用户/速度选择列）。
看起来像func getAlerts(setCompletion: @escaping (Bool) -> ()) {
self.mapView.removeAnnotations(mapView.annotations)
MapArray.alertNotificationCoordinatesArray.removeAll()
MapArray.userAlertNotificationArray.removeAll()
print(" MapArray.alertNotificationCoordinatesArray before getNewerAlerts is: \(MapArray.alertNotificationCoordinatesArray)")
print(" self.userAlertNotificationArray before getNewerAlerts is: \(MapArray.userAlertNotificationArray)")
ref = Database.database().reference()
// ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observe(.childAdded, with: { (snapshot) in
ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observe(DataEventType.childAdded, with: { (snapshot) in
// self.mapView.removeAnnotations(self.mapView.annotations) //
print(" added snapshot is: \(snapshot)")
guard let data = snapshot.value as? [String:String] else { return }
// guard let firebaseKey = snapshot.key as? String else { return }
let firebaseKey = snapshot.key
// let date = data!["Date"]
// let time = data!["Time"]
let dataLatitude = data["Latitude"]!
let dataLongitude = data["Longitude"]!
let type = data["Description"]!
let id = Int(data["Id"]!)
let userName = data["user"]!
let doubledLatitude = Double(dataLatitude)
let doubledLongitude = Double(dataLongitude)
let recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude!, longitude: doubledLongitude!)
let userAlertAnnotation = UserAlert(type: type, coordinate: recombinedCoordinate, firebaseKey: firebaseKey, title: type,id: id!, userName: userName)
MapArray.userAlertNotificationArray.append(userAlertAnnotation) // array of notifications coming from Firebase
MapArray.alertNotificationCoordinatesArray.append(recombinedCoordinate) // array for checkig alerts on route
print(" MapArray.alertNotificationCoordinatesArray after getNewerAlerts is: \(MapArray.alertNotificationCoordinatesArray)")
print(" self.userAlertNotificationArray after getNewerAlerts is: \(MapArray.userAlertNotificationArray)")
setCompletion(true)
self.mapView.addAnnotations(MapArray.userAlertNotificationArray)
})
// ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observe(.childRemoved, with: { (snapshot) in
ref?.child("Continent").child("Europe").child("Country").child("Italy").child("Region").child("Emilia-Romagna").child("City").child("Bologna").child("Community").child("Alert Notifications").observe(DataEventType.childRemoved, with: { (snapshot) in
print(" self.userAlertNotificationArray before getDeletedAlerts snapshot is: \(MapArray.userAlertNotificationArray)")
print(" MapArray.alertNotificationCoordinatesArray before getDeletedAlerts snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
print(" removed snapshot is: \(snapshot)")
guard let data = snapshot.value as? [String:String] else { return }
let firebaseKey = snapshot.key
// let date = data!["Date"]
// let time = data!["Time"]
let dataLatitude = data["Latitude"]!
let dataLongitude = data["Longitude"]!
let type = data["Description"]!
let id = Int(data["Id"]!)
let userName = data["user"]!
let doubledLatitude = Double(dataLatitude)
let doubledLongitude = Double(dataLongitude)
let recombinedCoordinate = CLLocationCoordinate2D(latitude: doubledLatitude!, longitude: doubledLongitude!)
_ = UserAlert(type: type, coordinate: recombinedCoordinate, firebaseKey: firebaseKey, title: type,id: id!, userName: userName)
MapArray.userAlertNotificationArray.removeAll(where: { ($0.firebaseKey == firebaseKey) }) //remove the alert
MapArray.alertNotificationCoordinatesArray.removeAll(where: { ($0.latitude == recombinedCoordinate.latitude && $0.longitude == recombinedCoordinate.longitude) })
self.mapView.removeAnnotations(self.mapView.annotations)
self.mapView.addAnnotations(MapArray.userAlertNotificationArray)
print(" self.userAlertNotificationArray after getDeletedAlerts snapshot is: \(MapArray.userAlertNotificationArray)")
print(" MapArray.alertNotificationCoordinatesArray after getDeletedAlerts snapshot is: \(MapArray.alertNotificationCoordinatesArray)")
setCompletion(true)
})
}
从那里，您可以对值执行简单的x = df.loc[["2-4-2018","2-4-2019"], ['users', 'speed']]或对值的索引执行x['users'].min()。
我还没有玩过Dataframe，但是您正在寻找如何切片 Dataframe。