CODEWITHSUNDEEP
javaarraysparsingmatrix
user3086819
user3086819

Reputation: 107

Remove Column with 0s on splitted Arrays

In a function I have as input two 2D Arrays(over 50x50), both with same Nr. of columns but different Nr. of Rows. Basically I need to remove the common columns containing digits from a range of 0 to 2

Example:

A: 3 0 0 0 0 1 0
   5 0 0 6 0 0 2
   2 0 0 7 1 0 0

B: 2 3 0 1 0 0 1
   4 9 0 2 0 0 0

In this case I would have to remove column 3 , 6 and 7(to A and B), since Column 3 has only 0s, Column six only 0s and 1s, and The last Column all Nr. from 0 to 2.

I could use a function like LinearAlgebra.deleteColumns(A , 2 , 5,6); and LinearAlgebra.deleteColumns(B, 2, 5,6); but since my input Array is huge, I'd have to do a column parsing comparing both arrays.

Any ideas to approach this? Here's a raw idea of using 3 for loops(java)

for(int col=0; col < A[0].length; col++){   // step through each column
    int cnt = 0;

    for(int row = 0; row < B.length ; row ++){ 
        if(!(B[col][row].equals(0 | 1 | 2))) {
            cnt++;       
        }
    }

    if(cnt == 0) {
        // store number of column -> use later on LinearAlgebra.deleteColumns
    }

    for(int row = 0; row < A.length  ; row++){        
        if(!(A[col][row].equals(0 | 1 | 2)))
        cnt++;             
    }
    if(cnt == 0){
        // check aswell all values of B otherwise iterate next column
    }  
}

Upvotes: 1

Views: 77

Answers (4)

giorashc
giorashc

Reputation: 13713

boolean result[] = new boolean[<num of columns>];
for (int i = 0; i < result.length; ++i)
    result[i] = true;

for (int row = 0; row < arrayA.length; ++row) {
   for (int col = 0; col < arrayA[row].length; ++col)
       result[col] &= arrayA[row][col] == 0; 
}

for (int row = 0; row < arrayB.length; ++row) {
       for (int col = 0; col < arrayB[row].length; ++col)
       result[col] &= arrayB[row][col] == 0; 
}

for (int i = 0; i < 6; ++i) 
    System.out.println(result[i]);

now each cell(column) in the result array will indicate which column contains zeros for both arrays.

*Note: * This assums as you said that both arrays have the same number of columns

EDIT due to comment:

If you want to delete columns whose values are in a certain inclusive range use this condition :

 result[col] &= arrayA[row][col] >= minRange && arrayA[row][col] <= maxRange;

for an exclusive range just remove the = sign

and do the same for the second array

Upvotes: 1

ifloop
ifloop

Reputation: 8386

Helper function: 

private boolean isColumnDeletable(final int column, final int[][] array) {
    for (int row = 0; row < array.length; row++) {
        if (array[row][column] != 0)
            return false;
    }

    return true;
}

Example usage:

int[][] values1 = new int[][] {{1, 1, 1, 0, 1}, {2, 2, 2, 0, 2}, {3, 3, 3, 0, 3}};
int[][] values2 = new int[][] {{4, 4, 4, 0, 4}, {5, 5, 5, 0, 5}};


for (int column = 0; column < values1[0].length; column++) {
    System.out.printf("Checking column %d: ", column + 1);

    if (isColumnDeletable(column, values1) && isColumnDeletable(column, values2))
        System.out.printf("Deletable!\n");
    else
        System.out.printf("Not deletable!\n");
}

Output:

Checking column 1: Not deletable!
Checking column 2: Not deletable!
Checking column 3: Not deletable!
Checking column 4: Deletable!
Checking column 5: Not deletable!

Upvotes: 1

Ceiling Gecko
Ceiling Gecko

Reputation: 3186

Make a boolean flag, loop over the columns and decide which ones to remove.

Example to find deletable columns:

boolean deleteFlag;
for ( int i = 0; i < columnAmount; i++ ) {
    deleteFlag = true;
    for (int j = 0; j < firstTableRowAmount; j++ ) {
        if (A[j][i] != 0) {
           deleteFlag = false;
           break;
        }
    }
    if(!deleteFlag) {
        continue;
    }
    for (int j = 0; j < secondTableRowAmount; j++ ) {
        if (B[j][i] != 0) {
           deleteFlag = false;
           break;
        }
    }
    if(deleteFlag) {
        callDeleteColumnFunction(i);
    }
}

and callDeleteColumnFunction(i) is a function which deletes the i-th column of both of the 2D arrays.

Upvotes: 1

Clad Clad
Clad Clad

Reputation: 2781

first of all you are maybe confusing your col and row order because you get the row count by using A[0].length but you use it in B[col][row] but for this part I let you see more in details.

anyways if I understand you problem well you are looking for the column that only contains 0.

For this you should first init a bool at true and when a value different than 0 you put it at false. using the same process for the second with another bool you finally compare the two bool to know if you have to delete the column ;)

Upvotes: 1

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