ST_ClusterKMeans()

Datum ST_ClusterKMeans

(

PG_FUNCTION_ARGS

)

Definition at line 173 of file lwgeom_window.c.

{
        WindowObject winobj = PG_WINDOW_OBJECT();
        kmeans_context *context;
        int64 curpos, rowcount;
 
        rowcount = WinGetPartitionRowCount(winobj);
        context = (kmeans_context *)
                WinGetPartitionLocalMemory(winobj,
                        sizeof(kmeans_context) + sizeof(int) * rowcount);
 
        if (!context->isdone)
        {
                int       i, k, N;
                bool      isnull, isout;
                LWGEOM    **geoms;
                int       *r;
 
                /* What is K? If it's NULL or invalid, we can't procede */
                k = DatumGetInt32(WinGetFuncArgCurrent(winobj, 1, &isnull));
                if (isnull || k <= 0)
                {
                        context->isdone = true;
                        context->isnull = true;
                        PG_RETURN_NULL();
                }
 
                /* We also need a non-zero N */
                N = (int) WinGetPartitionRowCount(winobj);
                if (N <= 0)
                {
                        context->isdone = true;
                        context->isnull = true;
                        PG_RETURN_NULL();
                }
 
                /* Error out if N < K */
                if (N<k)
                {
                        lwpgerror("K (%d) must be smaller than the number of rows in the group (%d)", k, N);
                }
 
                /* Read all the geometries from the partition window into a list */
                geoms = palloc(sizeof(LWGEOM*) * N);
                for (i = 0; i < N; i++)
                {
                        GSERIALIZED *g;
                        Datum arg = WinGetFuncArgInPartition(winobj, 0, i,
                                                WINDOW_SEEK_HEAD, false, &isnull, &isout);
 
                        /* Null geometries are entered as NULL pointers */
                        if (isnull)
                        {
                                geoms[i] = NULL;
                                continue;
                        }
 
                        g = (GSERIALIZED*)PG_DETOAST_DATUM_COPY(arg);
                        geoms[i] = lwgeom_from_gserialized(g);
                }
 
                /* Calculate k-means on the list! */
                r = lwgeom_cluster_2d_kmeans((const LWGEOM **)geoms, N, k);
 
                /* Clean up */
                for (i = 0; i < N; i++)
                        if (geoms[i])
                                lwgeom_free(geoms[i]);
 
                pfree(geoms);
 
                if (!r)
                {
                        context->isdone = true;
                        context->isnull = true;
                        PG_RETURN_NULL();
                }
 
                /* Safe the result */
                memcpy(context->result, r, sizeof(int) * N);
                pfree(r);
                context->isdone = true;
        }
 
        if (context->isnull)
                PG_RETURN_NULL();
 
        curpos = WinGetCurrentPosition(winobj);
        PG_RETURN_INT32(context->result[curpos]);
}

References kmeans_context::isdone, kmeans_context::isnull, lwgeom_cluster_2d_kmeans(), lwgeom_free(), lwgeom_from_gserialized(), r, and kmeans_context::result.

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