问题
I have a CSV file that contains roughly 500,000 rows and 22 columns of flight data. The 5th Column contains the tail number of each plane for each flight. The 22nd column contains the distance traveled for each flight. I'm attempting to sum the total distance traveled (column 22) for each tail number (column 5).
I created a HashMap containing all data named map1. I created a 2nd HashMap named planeMileages to place each flight number and its total distance traveled into. I'm using a nested if statement go through each line of map1 and see if the tail number is already contained in planeMileages. If it is in planeMileages, then I want to add on to the accumulatedMileagesfor that key. If it is not contained, I'd like to input the key along with it's first distance value.
The current code that I've written seems sound to me, but it is producing the wrong result, outputting the incorrect tail number. Can you please take a look and let me know what I am overlooking in my main method? Thanks!
public class FlightData {
HashMap<String,String[]> dataMap;
public static void main(String[] args) {
FlightData map1 = new FlightData();
map1.dataMap = map1.createHashMap();
HashMap<String, Integer> planeMileages = new HashMap();
//Filling the Array with all tail numbers
for (String[] value : map1.dataMap.values()) {
if(planeMileages.containsKey(value[4])) {
int accumulatedMileage = planeMileages.get(value[4]) + Integer.parseInt(value[21]);
planeMileages.remove(value[4]);
planeMileages.put(value[4], accumulatedMileage);
}
else {
planeMileages.put(value[4],Integer.parseInt(value[21]));
}
}
String maxKey = Collections.max(planeMileages.entrySet(), Map.Entry.comparingByValue()).getKey();
System.out.println(maxKey);
}
public HashMap<String,String[]> createHashMap() {
File flightFile = new File("flights.csv");
HashMap<String,String[]> flightsMap = new HashMap<String,String[]>();
try {
Scanner s = new Scanner(flightFile);
while (s.hasNextLine()) {
String info = s.nextLine();
String [] piecesOfInfo = info.split(",");
String flightKey = piecesOfInfo[4] + "_" + piecesOfInfo[2] + "_" + piecesOfInfo[11]; //Setting the Key
String[] values = Arrays.copyOfRange(piecesOfInfo, 0, piecesOfInfo.length);
flightsMap.put(flightKey, values);
}
s.close();
}
catch (FileNotFoundException e)
{
System.out.println("Cannot open: " + flightFile);
}
return flightsMap;
}
}
Please see a few lines of my CSV file below:
DayofMonth DayOfWeek FlightDate UniqueCarrier TailNum OriginAirportID Origin OriginStateName DestAirportID Dest DestStateName DepTime DepDelay WheelsOff WheelsOn ArrTime ArrDelay Cancelled CancellationCode Diverted AirTime Distance
3 1 10/3/2016 AA N786AA 10721 BOS Massachusetts 12478 JFK New York 556 -4 623 703 709 -6 0 0 40 187
4 2 10/4/2016 AA N794AA 10721 BOS Massachusetts 12478 JFK New York 554 -6 615 703 712 -3 0 0 48 187
1 6 10/1/2016 AA N783AA 12478 JFK New York 12892 LAX California 823 -7 844 1104 1111 -30 0 0 320 2475
2 7 10/2/2016 AA N798AA 12478 JFK New York 12892 LAX California 847 17 904 1131 1159 18 0 0 327 2475
3 1 10/3/2016 AA N786AA 12478 JFK New York 12892 LAX California 825 -5 838 1109 1131 -10 0 0 331 2475
4 2 10/4/2016 AA N794AA 12478 JFK New York 12892 LAX California 826 -4 848 1114 1132 -9 0 0 326 2475
回答1:
Hello can you check this?
public static void main(String[] args) throws IOException {
Map<String, String[]> map = createMap();
Map<String, Long> planeMileages = map
.entrySet()
.stream()
.collect(Collectors.groupingBy(o -> o.getValue()[4],
Collectors.collectingAndThen(
Collectors.summarizingInt(value ->
Integer.parseInt(value.getValue()[21])), IntSummaryStatistics::getSum
)
));
String maxKey = planeMileages.entrySet().stream().max(Comparator.comparing(Map.Entry::getValue)).get().getKey();
System.out.println("max key: "+ maxKey);
}
public static Map<String, String[]> createMap() throws IOException {
try (BufferedReader a = Files.newBufferedReader(Paths.get("flights.csv"))) {
return a.lines().map(s -> s.split(","))
.collect(Collectors.toMap(piecesOfInfo -> String.join("_", piecesOfInfo[4], piecesOfInfo[2], piecesOfInfo[11]), Function.identity()));
}
}
public static Map<String, String[]> createMapLastDupWins() throws IOException {
try (BufferedReader a = Files.newBufferedReader(Paths.get("flights.csv"))) {
return a.lines().map(s -> s.split(","))
.collect(Collectors.toMap(piecesOfInfo -> String.join("_", piecesOfInfo[4], piecesOfInfo[2], piecesOfInfo[11]), Function.identity(), (strings, strings2) -> {
//if this helps than data is duplicated
return strings2;
}));
}
}
回答2:
Here is a bit more OOP way of doing it.
You extend the HashMap and add two new methods, one for adding flights and another for calculating total distance. This way you are not constantly removing and adding back modified values into the HashMap. You can expand on this to fit your needs.
import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;
public class Main {
public static void main(String[] args) {
FlightData flightData = getFlightDataFromFile();
flightData.getDistanceTraveled("tail number");
}
public static FlightData getFlightDataFromFile() {
File flightFile = new File("flights.csv");
FlightData flightData= new FlightData();
try {
Scanner s = new Scanner(flightFile);
while (s.hasNextLine()) {
String info = s.nextLine();
String[] piecesOfInfo = info.split(",");
String tailNr= piecesOfInfo[4];
Flight flight = new Flight(piecesOfInfo[6], piecesOfInfo[9], Integer.parseInt(piecesOfInfo[21]));
flightData.addFlight(tailNr, flight);
}
s.close();
} catch (FileNotFoundException e) {
System.out.println("Cannot open: " + flightFile);
}
return flightData;
}
}
class FlightData extends HashMap<String,List<Flight>> {
void addFlight(String tailNr, Flight flight) {
computeIfAbsent(tailNr, flights -> new ArrayList<>()).add(flight);
}
int getDistanceTraveled(String tailNr) {
int distance = 0;
for (Flight f : get(tailNr)) distance+= f.distance;
return distance;
}
}
class Flight {
String from;
String to;
int distance;
public Flight(String from, String to, int distance) {
this.from = from;
this.to = to;
this.distance = distance;
}
}
回答3:
Try this , and if the miles are very huge change Integer to Long and then check
HashMap<String, Integer> planeMileages = new HashMap<>();
for (String [] value : flightsMap.values()) {
if(planeMileages.containsKey(value[4])) {
planeMileages.put(value[4], planeMileages.get(value[4])+Integer.valueOf(value[21]));
} else {
planeMileages.put(value[4], Integer.valueOf(value[21]));
}
}
来源：https://stackoverflow.com/questions/60696595/java-how-to-sum-all-the-values-of-one-column-based-on-the-criteria-in-a-second