How can I count the arraylist?

Question

I have tried Scanner to read a text file into an arraylist. Let's assume that I have an arraylist like this

[A, MANBA]
[A, PGD]
[A, GUSB]
[A, GLB1]
[B, HS6ST1]
[B, NDST1]
[B, NDST4]
[C, NRP1]
[C, ZEB1]

How can I count the occurrence of the first value and print it out ? As this particular example, the output will be

A  4
B  3
C  2

Here is the code I have so far. Any suggestion would be grateful.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class PI_list{
public static void main (String[] args) throws FileNotFoundException
{
    Scanner inputFile = new Scanner(new File("/home/tab.csv"));
    while(inputFile.hasNextLine()){
        String line = inputFile.nextLine();
        ArrayList<String> PPIData = new ArrayList<String>();
        Scanner scanner = new Scanner(line);
        scanner.useDelimiter("\t");
        while(scanner.hasNext()){
            PPIData.add(scanner.next());
        }
        scanner.close();

        System.out.println(PPIData);
    }

    inputFile.close();
    }
}

Should the count for A be 4 in your example?

Don Roby
– Don Roby

2014-05-13 10:30:22 +00:00
Commented May 13, 2014 at 10:30 — Don Roby
– Don Roby, Commented May 13, 2014 at 10:30
Don, you're right. A should be 4. Thanks.

user3631848
– user3631848

2014-05-13 11:26:07 +00:00
Commented May 13, 2014 at 11:26 — user3631848
– user3631848, Commented May 13, 2014 at 11:26

markusw · Accepted Answer · 2014-05-13 10:31:44Z

3

Have a look at guavas MultiMap. That's exactly what you are looking for.

answered May 13, 2014 at 10:31

markusw

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Comments

RMachnik · Accepted Answer · 2014-05-13 13:24:15Z

0

Method with simple for

public String countOccurences(String letter,List<String> array){
  int counter = 0; 
  for(String s : array){
      if(s.equals(letter))
        counter++;
   }
  return letter + ": " + String.valueOf(counter);
}

public void getResult(List<String> array){
  Set<String> setOfLetters = new HashSet<String>();
  List<String> dataArray = new ArrayList<String>();
  for(String s: array){
     s.replace("[","");
     s.replace("]","");
     String tab[] = s.split(",");
     setOfLetters.add(tab[0]);
     dateArray.add(tab[0]);
 }
 for(String s: setOfLetters)
    countOccurences(s,dataArray);
}

so simply your code should look like that

public static void main (String[] args) throws FileNotFoundException
{
    Scanner inputFile = new Scanner(new File("/home/tab.csv"));
    while(inputFile.hasNextLine()){
        String line = inputFile.nextLine();
        ArrayList<String> PPIData = new ArrayList<String>();
        Scanner scanner = new Scanner(line);
        scanner.useDelimiter("\t");
        while(scanner.hasNext()){
            PPIData.add(scanner.next());
        }
        scanner.close();
        getResult(PPIData);
        System.out.println(PPIData);
    }

Of course with access to my above methods.

Merging it all your class should look like

public class PI_list {

    public static String countOccurences(String letter, List<String> array) {
        int counter = 0;
        for (String s : array) {
            if (s.equals(letter))
                counter++;
        }
        return letter + ": " + String.valueOf(counter);
    }

    public static void getResult(List<String> array) {
        Set<String> setOfLetters = new HashSet<String>();
        List<String> dataArray = new ArrayList<String>();
        for (String s : array) {
            s.replace("[", "");
            s.replace("]", "");
            String tab[] = s.split(",");
            setOfLetters.add(tab[0]);
            dataArray.add(tab[0]);
        }
        for (String s : setOfLetters)
            System.out.println(countOccurences(s, dataArray));
    }

    public static void main(String[] args) throws FileNotFoundException {
        Scanner inputFile = new Scanner(new File("/home/tab.csv"));
        while (inputFile.hasNextLine()) {
            String line = inputFile.nextLine();
            ArrayList<String> PPIData = new ArrayList<String>();
            Scanner scanner = new Scanner(line);
            scanner.useDelimiter("\t");
            while (scanner.hasNext()) {
                PPIData.add(scanner.next());
            }
            getResult(PPIData);
            System.out.println(PPIData);
        }
        inputFile.close();
    }

}

edited May 13, 2014 at 13:24

answered May 13, 2014 at 10:30

RMachnik

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11 Comments

user3631848 Over a year ago

Thanks for helping. However, I still don't know where should i put this for loop ? just before the second while loop ?

RMachnik Over a year ago

Look on my above post again. I wrote more.

user3631848 Over a year ago

Do you mean add your method before or after to the main function ? What do you mean by access to the method ?

RMachnik Over a year ago

Access it means you have to put them into class that method main is run. So simply in class PI_list. But I think that you have to change accessors of that methods for public static.... Thansk in advance for accepting answer. :)

user3631848 Over a year ago

i know i have to put it into PI_list class, but I don't know how/where. I have tried to put it into the second while loop but failed. Maybe it looks trivial to you, but I really stuck over this. I'm really at very beginning stage of Java. It takes me two days to reach here.

|

mohamedrias · Accepted Answer · 2014-05-13 10:38:46Z

0

As per your code

while(inputFile.hasNextLine()){
        String line = inputFile.nextLine();
        ArrayList<String> PPIData = new ArrayList<String>();
        Scanner scanner = new Scanner(line);
        scanner.useDelimiter("\t");
        while(scanner.hasNext()){
            PPIData.add(scanner.next());
        }
        scanner.close();

        System.out.println(PPIData);
    }

    inputFile.close();
    }

The arraylist is locally scoped so you can't use it outside the while loop.

In case you want to use it later some point to count the occurances of letter, then declare it above the while loop.

Steps for solution:

Iterate through the arrayList
Get the first element which will contain [A, MANBA] as string
Split the string based on comma, get the value A
Now pass the value A to a function where you will check the occurrences of A in the ArrayList.

Mostly this will give you concurrency exception as you will be processing same arraylist.

Better solution:

Use guava-libraries Multimap which will be easier for your scenario

answered May 13, 2014 at 10:38

mohamedrias

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1 Comment

user3631848 Over a year ago

Thanks for your quick help. I'm very new in coding java. I guess I understand what you mean, but still don't know how to do. I prefer your four steps solution, by the way.

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