Split a List of Strings based on value in Java

Question

What I want to do is to split an array of strings, when the first 6 characters in the string are zeroes ("000000") or when all the digits in the string are zeroes. Limiting to 6 characters won't be very dynamic.

I got this code, and it does what I want to achieve.

import java.util.*;
public class Main
{
    public static void main(String[] args) {
            ArrayList<String> unsplitted = new ArrayList<String>();
  
            unsplitted.add("000000: this_should_go_into_first_array");
            unsplitted.add("000234: something1");
            unsplitted.add("0000ff: something2");
            unsplitted.add("000111: something3");
            unsplitted.add("000051: something4");
            unsplitted.add("007543: something5");
            unsplitted.add("000000: and_this_should_go_into_second_array");
            unsplitted.add("005612: something7");
            unsplitted.add("005712: something8");
  
            System.out.println("Unsplitted list: "+ unsplitted);

            List<String> arrlist1 = unsplitted.subList(0, 6);
            List<String> arrlist2 = unsplitted.subList(6, unsplitted.size());
  
            System.out.println("Sublist of arrlist1: "+ arrlist1);
            System.out.println("Sublist of arrlist2: "+ arrlist2);
    }
}

Which prints out the wanted results

Sublist of arrlist1: [000000: this_should_go_into_first_array, 000234: something1, 0000ff: something2, 000111: something3, 000051: something4, 007543: somethi
ng5]                                                                                                                                                          
Sublist of arrlist2: [000000: and_this_should_go_into_second_array, 005612: something7, 005712: something8]

However, I don't know the indexes for the zeroes beforehand, so how can I achieve the same result by finding the zeroes dynamically?

Silvinus · Accepted Answer · 2021-04-19 22:15:43Z

1

You can simply iterate in your array and create "bucket" each time you detect your 000000 string :

ArrayList<String> unsplitted = new ArrayList<String>();

    unsplitted.add("000000: this_should_go_into_first_array");
    unsplitted.add("000234: something1");
    unsplitted.add("0000ff: something2");
    unsplitted.add("000111: something3");
    unsplitted.add("000051: something4");
    unsplitted.add("007543: something5");
    unsplitted.add("000000: and_this_should_go_into_second_array");
    unsplitted.add("005612: something7");
    unsplitted.add("005712: something8");

    List<List<String>> results = new ArrayList<>();
    unsplitted.forEach(w -> {
        if(w.startsWith("000000") || results.isEmpty()) {
            // no bucket or detect 000000
            List<String> bucket = new ArrayList<>();
            bucket.add(w);
            results.add(bucket);
        }
        else {
            // not contains 00000 put the value in the last bucket
            results.get(results.size() - 1).add(w);
        }
    });

    results.forEach(w -> {
        System.out.println("Sublist " + w);
    });

Is it the result that you expected ?

The result :

Sublist [000000: this_should_go_into_first_array, 000234: something1, 0000ff: something2, 000111: something3, 000051: something4, 007543: something5]
Sublist [000000: and_this_should_go_into_second_array, 005612: something7, 005712: something8]

edited Apr 19, 2021 at 22:15

answered Apr 19, 2021 at 22:09

Silvinus

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2 Comments

klabbaparn Over a year ago

Question: Why do I need the results.get(results.size() - 1).add(w);? I tried with results.add(w) but of course it didn't work. Just curious why I need to get the indexes first, and then add w

Silvinus Over a year ago

Result is a list of sublist. The-1 is to get the latest sublist that keep your string.

Marco Tizzano · Accepted Answer · 2021-04-19 22:50:57Z

The question is quite interesting. There are different way to implement this, but I am going to show you a solution where it can be applied with any length of the first part, which we can consider as a key.
As you said in your introduction, it wouldn't be dynamic if the check was limited to only 6 characters. Based on this, as an example, you can take the position of the character ':' as reference and apply a partitioning among the elements of the array.
Here is the solution I propose:

import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main
{
    public static void main(String[] args) {
        ArrayList<String> unsplitted = new ArrayList<String>();



        unsplitted.add("000000: this_should_go_into_first_array");
        unsplitted.add("000234: something1");
        unsplitted.add("0000ff: something2");
        unsplitted.add("000111: something3");
        unsplitted.add("000051: something4");
        unsplitted.add("007543: something5");
        unsplitted.add("000000: and_this_should_go_into_second_array");
        unsplitted.add("005612: something7");
        unsplitted.add("005712: something8");

        System.out.println("Non-split list: "+ unsplitted);

        Predicate<String> filter = (String s) -> {
            int indexOfCol = s.indexOf(":");

            return s.substring(0, indexOfCol).equals("0".repeat(indexOfCol));
        };

        Map<Boolean, List<String>> splitMap = unsplitted.stream()
                                                        .collect(Collectors.partitioningBy(filter));

        List<String> arrayZeroStart = splitMap.get(true);
        List<String> arrayNonZeroStart = splitMap.get(false);

        System.out.println("Sublist of arrayZeroStart: "+ arrayZeroStart);
        System.out.println("Sublist of arrayWithout: "+ arrayNonZeroStart);
    }
}

And here is the output:

Non-split list: [000000: this_should_go_into_first_array, 000234: something1, 0000ff: 

something2, 000111: something3, 000051: something4, 007543: something5, 000000: and_this_should_go_into_second_array, 005612: something7, 005712: something8]
Sublist of arrayZeroStart: [000000: this_should_go_into_first_array, 000000: and_this_should_go_into_second_array]
Sublist of arrayWithout: [000234: something1, 0000ff: something2, 000111: something3, 000051: something4, 007543: something5, 005612: something7, 005712: something8]

Btw, thank you for the attention and consideration, that's very appreciated!

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