A bit closer to a solution but still stuck

Question about the task

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I get the error: error: cannot find symbol if(map.getValue().equals(value)){//to compare the value with next value?? ^ How to solve this?

Create a Map<String, String> and add ten entries that represent (last name, first name) pairs.
Remove people with the same first name.

Requirements:

The program should not display text on the screen.
The program should not read values from the keyboard.
The createMap() method must create and return a HashMap that has (String, String) elements and contains 10 entries.
The removeFirstNameDuplicates() method must remove from the map all people who have the same first name.
The removeFirstNameDuplicates() method must call the removeItemFromMapByValue() method.

package com.codegym.task.task08.task0817; import java.util.HashMap; import java.util.Map; import java.util.*; /* We don't need repeats */ public class Solution { public static HashMap<String, String> createMap() { //write your code here HashMap<String, String> map = new HashMap<>(); map.put("LastName1", "Name1");//create a HashMap with 10 key-value pairs (lastName , name) map.put("LastName2", "Name1");//changed the first letter to capitals map.put("LastName3", "Name5");//changed the name of the HashMap from names to map map.put("LastName4", "Name7");//still not working why? map.put("LastName5", "Name9");// keys CANNOT be the same map.put("LastName6", "Name10");//values can be the same but NOT the keys map.put("LastName7", "Name11"); map.put("LastName8", "Name13"); map.put("LastName9", "Name14"); map.put("LastName10", "Name15"); return map; } public static void removeFirstNameDuplicates(HashMap<String, String> map) {// should this not be HashMap instead of Map? Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();//create an iterator for(Map.Entry<String, String> entry: map.entrySet())//loop over all the pairs in map { while(iterator.hasNext())// check is there is a next element in the Map { Map.Entry<String, String> pair = iterator.next();//gives next element String key = pair.getKey();// to find a particular key but why would I do this? String value = pair.getValue(); //get the value of this pair this is now working after removing (key) //how to get a value in order ro compare it with another value and to see if they are the same if(map.getValue().equals(value)){//to compare the value with next value?? removeItemFromMapByValue();// this should call the method to remove this element. } } } } public static void removeItemFromMapByValue(Map<String, String> map, String value) { HashMap<String, String> copy = new HashMap<String, String>(map); for (Map.Entry<String, String> pair : copy.entrySet()) { if (pair.getValue().equals(value)) map.remove(pair.getKey()); } } public static void main(String[] args) { } }

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Liliane Top

Level 17 , Amsterdam, Netherlands

20 February 2020, 18:07

public static void removeFirstNameDuplicates(Map<String, String> map) {
        Collection<String> x = map.values();//I assign all the values from the map to the collection
        ArrayList<String> listToRemoveItems = new ArrayList<>(x);// I assign the values to a new ArrayList called mapToremoveItems
        for (int i = 0; i < listToRemoveItems.size(); i++) {// loop over the ArrayList listToRemoveItems
            if (Collections.frequency(listToRemoveItems, listToRemoveItems.get(i)) > 1) { //checks if the values are duplicated
                removeItemFromMapByValue(map, listToRemoveItems.get(i));//call the method that removes the double items from the original map
                listToRemoveItems.set(i, "");//replaces the duplicated item with an empty String in the ArrayList
            }
            //System.out.println(listToRemoveItems.get(i));
        }
    }




    public static void removeItemFromMapByValue(Map<String, String> map, String value) {
        HashMap<String, String> copy = new HashMap<String, String>(map);
        for (Map.Entry<String, String> pair : copy.entrySet()) {
            if (pair.getValue().equals(value))
                map.remove(pair.getKey());
        }
        //System.out.println(map);
    }

    public static void main(String[] args) {

       // removeFirstNameDuplicates(createMap());//de ene functie in de andere functie aanroepen

    }
}

Artem Divertitto Senior Android Developer at United Tech

21 February 2020, 09:10

1.  if (Collections.frequency(listToRemoveItems, listToRemoveItems.get(i)) > 1) { //checks if the values are duplicated

This method return how many times string listToRemoveItems.get(i) meets at listToRemoveItems.

Liliane Top

Level 17 , Amsterdam, Netherlands

21 February 2020, 09:28

Hi Tiym, Not sure how to respond ... Do you maybe have a link to an article that explains a bit more how the code above works? I just duplicated this from another trainee but do not understands how it works. I basically do not understand level 8 after lesson 8. I just keep going but almost every tasks that follows is beyond my comprehension. Please advice what I can do get a better understanding of this topic. Thanks for your effort anyways!

Artem Divertitto Senior Android Developer at United Tech

18 February 2020, 14:29

1. map.getValue().equals(value) Maybe you would like to use entry.getValue()? Map doesn't have getValue() method. 2. removeItemFromMapByValue - you don't send parameters into this method. This method has two parameters: Map map, String value 3. If you try remove element from map, you will get ConcurrentModificationException. You can copy original map, and work with it, and then remove from original map(send to method removeItemFromMapByValue)

Liliane Top

Level 17 , Amsterdam, Netherlands

20 February 2020, 18:05

Hi Tiym, First thanks so much for responding. This is my solution which I sort of got from someone else in my class. I still not completely sure how it works and having a hard time to find more indepth information how it actually works. Maybe you have a link to some article or something else to get a better understanding of what we're doing here? I tries to paste the code in but is exceeds the limit....

Guadalupe Gagnon

Level 37 , Tampa, United States

17 February 2020, 18:28

There is no .getValue() method that is part of the HashMap class.

Liliane Top

Level 17 , Amsterdam, Netherlands

17 February 2020, 21:27

I'm very confused I copied this code from the previous task that also works with HashMap... I don't understand how it works. Can you help me please?

Liliane Top

Level 17 , Amsterdam, Netherlands

17 February 2020, 21:29

in the task census I used this code: public static int getSameFirstNameCount(HashMap<String, String> map, String name) { Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();//create an iterator int count = 0;//create and intialize the int count while(iterator.hasNext())//loops over all the strings checks if there is a next { Map.Entry<String, String> pair = iterator.next();// get the next if(pair.getValue().equals(name)){// compares the values in the pair key-value (lastName, name) with name count++;// if there are values(name) that are the same +1 } } System.out.println(count); return count;// gives the total number of people with the same name }

Guadalupe Gagnon

Level 37 , Tampa, United States

18 February 2020, 04:15

The correct method is:

public static void removeFirstNameDuplicates(Map<String, String> map){

}

When you change the code the verification system can not validate your task. There is only one (Map) parameter in that method, not (Hashmap, String).You are going to have to use that method. You will need to figure out how to check for duplicate values (names) and remove them. Are you using intelliJ? If not then you will want to. When you use a variable of any type, intelliJ will automatically give you a list of methods you can use. You should go through them and see if any of them could be of use to you, and try ones out that you think could be. I will give you a hint, a great method for this task is Collections.frequency().

Guadalupe Gagnon

Level 37 , Tampa, United States

18 February 2020, 04:17

Another hint is it is a lot easier to create a copy of the passed in Map because you cannot use the method removeItemFromMapByValue() while iterating over the map. The requirements specify that it must be used.