xnmode.c

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#include <stdlib.h>

#include <grass/gis.h>
#include <grass/raster.h>
#include <grass/calc.h>

/**********************************************************************
mode(x1,x2,..,xn)
   return mode of arguments
**********************************************************************/

static int dcmp(const void *aa, const void *bb)
{
    const double *a = aa;
    const double *b = bb;

    if (*a < *b)
        return -1;
    if (*a > *b)
        return 1;
    return 0;
}

static double mode(double *value, int argc)
{
    /* Nota:
     * It might be safer for to return nan or inf in case the input is empty,
     * but it is a misuse of the function, so the return value is sort of
     * undefined in that case.
     */
    double mode_v = 0.0;
    int mode_n = 0;
    int i;

    qsort(value, argc, sizeof(double), dcmp);

    for (i = 0; i < argc;) {
        int n = 1;
        double v = value[i];

        for (i++; i < argc; i++) {
            if (value[i] != v)
                break;
            n++;
        }

        if (n < mode_n)
            continue;

        mode_v = v;
        mode_n = n;
    }

    return mode_v;
}

int f_nmode(int argc, const int *argt, void **args)
{
    static double *value;
    static int value_size;
    int size = argc * sizeof(double);
    int i, j;

    if (argc < 1)
        return E_ARG_LO;

    for (i = 1; i <= argc; i++)
        if (argt[i] != argt[0])
            return E_ARG_TYPE;

    if (size > value_size) {
        value_size = size;
        value = G_realloc(value, value_size);
    }

    switch (argt[argc]) {
    case CELL_TYPE:
        {
            CELL *res = args[0];
            CELL **argv = (CELL **) & args[1];

            for (i = 0; i < columns; i++) {
                int n = 0;

                for (j = 0; j < argc; j++) {
                    if (IS_NULL_C(&argv[j][i]))
                        continue;
                    value[n++] = (double)argv[j][i];
                }

                if (!n)
                    SET_NULL_C(&res[i]);
                else
                    res[i] = (CELL) mode(value, n);
            }
            return 0;
        }
    case FCELL_TYPE:
        {
            FCELL *res = args[0];
            FCELL **argv = (FCELL **) & args[1];

            for (i = 0; i < columns; i++) {
                int n = 0;

                for (j = 0; j < argc; j++) {
                    if (IS_NULL_F(&argv[j][i]))
                        continue;
                    value[n++] = (double)argv[j][i];
                }

                if (!n)
                    SET_NULL_F(&res[i]);
                else
                    res[i] = (FCELL) mode(value, n);
            }
            return 0;
        }
    case DCELL_TYPE:
        {
            DCELL *res = args[0];
            DCELL **argv = (DCELL **) & args[1];

            for (i = 0; i < columns; i++) {
                int n = 0;

                for (j = 0; j < argc; j++) {
                    if (IS_NULL_D(&argv[j][i]))
                        continue;
                    value[n++] = (double)argv[j][i];
                }

                if (!n)
                    SET_NULL_D(&res[i]);
                else
                    res[i] = (DCELL) mode(value, n);
            }
            return 0;
        }
    default:
        return E_INV_TYPE;
    }
}