添加和删​​除 ArrayList 中的元素设置为哈希图中的值 [英] Adding and deleting elements in ArrayList set as a value in a hashmap

问题描述

所以我有一个看起来像这样的文件:

So I have a file that looks like this:

    1st 2nd­ nth
    e1­, ­­v1, 1
    e1, v3, 2
    e1, v4, 4
    e1, v5, 7
    e2, v1, 1
    ., ­., .
    ., ­., .
    ., ­., .

我希望第一列是哈希图的键(e1、e2 或 e3)，值是一个名为Ratings"的 ArrayList，我希望第二列有它的值(一个int)，在数组列表的第 n 个索引内.

where I want the first column to be the key of a hashmap (e1, or e2, or e3), and the value to be an ArrayList called "Ratings" that in I want the second column to have it's value (an int), inside the nth index of the arraylist.

到目前为止，这是我的全部代码:

Here is my code in it's entirety so far:

import java.util.*;
import java.io.*;

public class Setup
{
    public static void Setup(String[] args)
    {
        String user;
        int value, location;
        //Create a Hashmap that holds a string key and an ArrayList value
        HashMap<String, ArrayList<Integer>> userRatings = new HashMap<String, ArrayList<Integer>>();
        try
        {
            BufferedReader bufferReader = new BufferedReader(new FileReader("Student list.txt")); //read from file
            String line, sentence; //declare two string variables
            String[] sData; //declare a string array (store the contents here)
            line = bufferReader.readLine(); //Read the line
            while (line != null) //While there is a line, do this:
            {
                line = bufferReader.readLine();
                sData  = line.split(", "); //Into the string array, enter individual values in the line split by the ", " characters
                int iData[] = new int[sData.length]; //Create an int array the size of the string array
                user = sData[0];
                for (int i = 0; i <sData.length; i++) //fill the int array with the int-version of the string array
                {
                    iData[i] = Integer.parseInt(sData[i]); //pass the strings as integers into the integer array
                }
                value = iData[1];
                location = iData[2];
                if(!userRatings.containsKey(user)) //The user does not have ratings.
                {
                    ArrayList<Integer> ratings = new ArrayList<Integer>();
                    //                     ratings = userRatings.get(user);
                    for (int j = 0; j < 50; j++)
                    {
                        ratings.add(j);
                    }
                    System.out.println(user + " " + userRatings.get(user));

                }
                else //The user has ratings
                {
                    userRatings.get(user).add(location,value);
                    System.out.println(user + " " + userRatings.get(user));
                }
            }
            bufferReader.close();
        }    catch (FileNotFoundException e)
        {
            System.out.println("File does not exist or could not be found.");
        }
        catch (IOException e)
        {
            System.out.println("Can't read from file");
        }
        catch (NullPointerException e)
        {
        }
    }
}

我在修改数组列表的内容时遇到问题.

I am having a problem with modifying the contents of the arraylist.

总结:文件第一列中的每个字符串在哈希映射(userList)中都有自己的键程序将检查它是否有键，如果不存在键，它将创建一个新的数组列表作为键的值.arrayList 将填充 50 个索引，其中包含0".之后，arraylist 将从文件中添加新值，其中第二列中的整数将添加到第 n 列的相应值处.

To sum up: Every string in the 1st column of the file would have it's own key in the hashmap (userList) The program will check if it has the key, if no key exists, it will create a new arraylist as the value for the key. The arrayList will be populated with 50 indexes, of which they will contain "0". After that, the arraylist will have new values added from the file in which the integer in the second column will be added at the corresponding value of the nth column.

我将如何填充数组列表，以及如何编辑它，以便如果我想在用户 e6 的第 n 个索引处添加一个新整数，我可以?

How would I populate the arraylist, and how would I edit it so that if I want to add a new integer at the nth index of user e6, I could?

推荐答案

当你的 Map 中不存在给定的键时，你必须添加一个新的键值对

When given key is not present in your Map you have to add a new Key value pair

if(!userRatings.containsKey(user)) //The user does not have ratings.
{
   ArrayList<Integer> ratings = new ArrayList<Integer>();                   
   for (int j = 0; j < 50; j++) {
       ratings.add(j);
  }
  userRatings.put(user, ratings); // place new mapping 
  System.out.println(user + " " + userRatings.get(user));
} else //The user has ratings
{
    ArrayList<Integer> ratings  = userRatings.get(user);
    ratings.add(location,value); // Update your list with location and value
    System.out.println(user + " " + userRatings.get(user)); 
}

iData[i] = Integer.parseInt(sData[i]); 鉴于您的文件内容它会抛出 NumberFormatException 因为无法解析 v1，这将不起作用内部

iData[i] = Integer.parseInt(sData[i]); This will not work given your file content it will throw NumberFormatException as v1 cannot be parsed to int.

相反，您可以执行以下操作:

Instead you can do something like this:

value = Integer.parseInt(sData[1].trim().substring(1));
location = Integer.parseInt(sData[2].trim());

比较两个键的值:

方法一

ArrayList<Integer> first = userRatings.get(e1);
ArrayList<Integer> second = userRatings.get(e2);

//Taking the smallest size will ensure that we don't get IndexOutOfBoundsException.

int length = first.size() < second.size() ? first.size() : second.size();

for(int iDx = 0; iDx < legth; iDx++){
   //compare content
}

方法二

ArrayList<Integer> first = userRatings.get(e1);
ArrayList<Integer> second = userRatings.get(e2);

Arrays.equals(first.toArray(), second.toArray());

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