CODEWITHSUNDEEP
javamatrixdata-structures
Johy
Johy

Reputation: 317

Java dynamic matrix structure

I'm wondering about the best way to implement a matrix in Java in which columns and rows have to be easily added/removed.

Something like double[][] matrix seems quite heavy when it comes to column/row removal.

I did some searches but could not find a design pattern (or so) dealing with this. Do you have any suggestion? I'm not looking for a library but more some guidelines on what is needed. I was thinking of a mix of Lists and Maps but I'm not sure that's the most efficient.

This link provides a bit of help but I'm sure there is a design pattern for this, or at least a nice way to do it.

Here are some more specifications: I expect the matrix to be 300x300 big in general. I need to do many manipulations though (I'm doing a heuristic that updates it a lot, hundreds times/sec), thus I can't browse it every time I want to update it. There's no maximum size but I don't expect it to be larger that 5000x5000.

Upvotes: 1

Views: 2043

Answers (3)

Micho
Micho

Reputation: 3963

Have a look at this implementation here. It looks like what you're looking for.

Upvotes: 1

WoDoSc
WoDoSc

Reputation: 2618

A possible simple solution would be the use of a List of List, like 

int nRows = 8, nCols = 4;
List<List<Double>> matrix = new ArrayList<>(nRows);
for (int k = 0; k < nRows; k++) {
    matrix.add(new ArrayList<>(nCols));
}

In this case would be really easy to add/remove a row, but a little tricky to add/remove a column.

void removeRow(ArrayList<ArrayList<Double>> matrix, int rowIndexToRemove) {
    matrix.remove(rowIndexToRemove);
}

void removeColumn(ArrayList<ArrayList<Double>> matrix, int coulmnIndexToRemove) {
    for (ArrayList<Double> row : matrix) {
        row.remove(coulmnIndexToRemove);
    }
}

void addRow(ArrayList<ArrayList<Double>> matrix, int rowIndexWhereInsert, ArrayList<Double> newRow) {
    matrix.add(rowIndexWhereInsert, newRow);
}

void addColumn(ArrayList<ArrayList<Double>> matrix, int columnIndexWhereInsert, ArrayList<Double> newColumn) {
    for (int k = 0; k < matrix.size(); k++) {
        ArrayList<Double> row = matrix.get(k);
        row.add(columnIndexWhereInsert, newColumn.get(k));
    }        
}

Upvotes: 3

Nadir
Nadir

Reputation: 1379

I suggest you to create your own class for this, similar to this

class Matrix{
int rows
int cols
List<MatrixElement> elements;
//some methods like getCols(), getRows()
}

class MatrixElement{
int row
int col
double value
//some methods like boolean isNeighbourOf(MatrixElement other) etc whatever you need

}

Such thing is quite easy to implement and gives you all the flexibility you need when using

Upvotes: 1

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