CODEWITHSUNDEEP
javaarrays
Petrov Kowalski
Petrov Kowalski

Reputation: 21

Filtering out an array

I have this one boolean array [true,false,false,true,true] and want to split a 2d array using it. what I tried doing is

public static void sorting(boolean[] test, String[][] arr)
   {
       int counter = 0;
       //finds how many people passed
       for(int z = 0; z < arr.length; z++)
       {
           if (test[z] != false)
               counter++;
               
       }
       String[][] passed = new String[counter][2];
       //tests for which people had Passed and copies it over
       for(int x = 0; x < passed.length; x++)
       {
           for(int y = 0; y < passed[x].length; y++)
           if(arr[x] != false)
               passed[x][y] = arr[x][y];
       }
       example2dArrayPrint(passed);
   }

an input I would have is

Bob A
Fred F
Larry F
John C
Tom B

and the output would be

Bob A
John C
Tom B

I don't see why this will not properly sort. EDIT

the relation between the 2 arrays is, if test[0] == true, that part of arr[0][0] and arr[0][1] would be put into the new passed array, false would be skipped over.
EDIT2

Changed passed from 3 to 2, was a mistype while making this.

Upvotes: 0

Views: 60

Answers (3)

WJS
WJS

Reputation: 40034

Here is a different approach using streams. I renamed the method to filtering as that is what you are doing, not sorting.

String[][] data = { { "Bob", "A" }, { "Fred", "F" },
        { "Larry", "F" }, { "John", "C" }, { "Tom", "B" } };

boolean[] test = { true, false, false, true, true };

String[][] result = filtering(test, data);
for (String[] a : result) {
    System.out.println(Arrays.toString(a));
}

Prints

[Bob, A]
[John, C]
[Tom, B]
  • Stream an array of ints from 0 to 4 inclusive using the array length of the test array.
  • then filter those indices on the boolean in the test array.
  • map the array associated with each index and return the arrays.
public static String[][] filtering(boolean[] test,
        String[][] arr) {
    return IntStream.range(0, test.length).filter(i -> test[i])
                .mapToObj(i -> arr[i]).toArray(String[][]::new);
}

Upvotes: 1

user8234870
user8234870

Reputation: 

public static void sorting(boolean[] test, String[][] arr){
       int counter = 0;
       //finds how many people passed
       for(int z = 0; z < arr.length; z++){
           if (test[z])
               counter++;
       }
       //cols represents number of columns you have in your 2d matrix.
       int cols=2;
       String[][] passed = new String[counter][2];
       counter=0;
       //out loop for iterating over arr
       for(int i=0;i<arr.length;i++)
            if(test[i]){
                //for all cols
                for(int j=0;j<cols;j++){
                    passed[counter][j]=arr[i][j];
                }
                counter++;
            }
       example2dArrayPrint(passed);
}

Upvotes: 0

Gurwinder Singh
Gurwinder Singh

Reputation: 39477

You have to keep two different pointers - one for current position in passed array and another in the input arr. Try this:

public static void sorting(boolean[] test, String[][] arr) {
    int counter = 0;
    //finds how many people passed
    for (int z = 0; z < arr.length; z++) {
        if (test[z])
            counter++;

    }
    String[][] passed = new String[counter][2];
    int i = 0;
    //tests for which people had Passed and copies it over
    for (int x = 0; x < arr.length; x++) {
        if (test[x]) {
            for (int y = 0; y < 2; y++) {
                passed[i][y] = arr[x][y];
            }
            i++;
        }
    }

    example2dArrayPrint(passed);
}

Outputs:

[[Bob, A], [John, C], [Tom, B]]

Upvotes: 1

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