Question

How to sort specific column of a matrix in C

Answer 1

#include <stdio.h>  
#include <stdlib.h> 

#define COLS 4

int compare(const void* a, const void* b) {
    return (*(int*)a - *(int*)b);
}

void sort_column(int matrix[][COLS], int rows, int col) {
    int* parr = (int*)malloc(rows * sizeof(int));

    for (int i = 0; i < rows; i++) {
        parr[i] = matrix[i][col];
    }
    
    qsort(parr, rows, sizeof(int), compare);

    for (int i = 0; i < rows; i++) {
        matrix[i][col] = parr[i];
    }

    free(parr);
}

int main()
{
    int matrix[][4] = {
                    {8, 3, 5, 1},
                    {4, 7, 6, 5},
                    {9, 1, 0, 4}
    };

    int rows = (sizeof(matrix) / sizeof(matrix[0]));
    int cols = (sizeof(matrix) / sizeof(matrix[0][0])) / rows;

    sort_column(matrix, rows, 1);

    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%2d", matrix[i][j]);
        }
        printf("\n");
    }

    return 0;
}





/*

run:

 8 1 5 1
 4 3 6 5
 9 7 0 4

*/

 

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