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sorted_array_to_mode.c
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sorted_array_to_mode.c
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Datum sorted_array_to_mode(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(sorted_array_to_mode);
/**
* Returns a mode from an (unsorted) array of numbers.
* by Paul A. Jungwirth
*/
Datum
sorted_array_to_mode(PG_FUNCTION_ARGS)
{
// Our arguments:
ArrayType *vals;
// The array element type:
Oid valsType;
// The array element type widths for our input array:
int16 valsTypeWidth;
// The array element type "is passed by value" flags (not really used):
bool valsTypeByValue;
// The array element type alignment codes (not really used):
char valsTypeAlignmentCode;
// The array contents, as PostgreSQL "Datum" objects:
Datum *valsContent;
// List of "is null" flags for the array contents (not used):
bool *valsNullFlags;
// The size of the input array:
int valsLength;
float8 *floatVals;
int i, j;
valcount *counts;
float8 v;
if (PG_ARGISNULL(0)) {
ereport(ERROR, (errmsg("Null arrays not accepted")));
}
vals = PG_GETARG_ARRAYTYPE_P(0);
if (ARR_NDIM(vals) == 0) {
PG_RETURN_NULL();
}
if (ARR_NDIM(vals) > 1) {
ereport(ERROR, (errmsg("One-dimesional arrays are required")));
}
if (array_contains_nulls(vals)) {
ereport(ERROR, (errmsg("Array contains null elements")));
}
// Determine the array element types.
valsType = ARR_ELEMTYPE(vals);
if (valsType != INT2OID &&
valsType != INT4OID &&
valsType != INT8OID &&
valsType != FLOAT4OID &&
valsType != FLOAT8OID) {
ereport(ERROR, (errmsg("Mode subject must be SMALLINT, INTEGER, BIGINT, REAL, or DOUBLE PRECISION values")));
}
valsLength = (ARR_DIMS(vals))[0];
get_typlenbyvalalign(valsType, &valsTypeWidth, &valsTypeByValue, &valsTypeAlignmentCode);
// Extract the array contents (as Datum objects).
deconstruct_array(vals, valsType, valsTypeWidth, valsTypeByValue, valsTypeAlignmentCode,
&valsContent, &valsNullFlags, &valsLength);
if (valsLength == 0) PG_RETURN_NULL();
// Compute the mode.
floatVals = palloc(sizeof(float8) * valsLength);
switch (valsType) {
case INT2OID:
for (i = 0; i < valsLength; i++) {
floatVals[i] = DatumGetInt16(valsContent[i]);
}
break;
case INT4OID:
for (i = 0; i < valsLength; i++) {
floatVals[i] = DatumGetInt32(valsContent[i]);
}
break;
case INT8OID:
for (i = 0; i < valsLength; i++) {
floatVals[i] = DatumGetInt64(valsContent[i]);
}
break;
case FLOAT4OID:
for (i = 0; i < valsLength; i++) {
floatVals[i] = DatumGetFloat4(valsContent[i]);
}
break;
case FLOAT8OID:
for (i = 0; i < valsLength; i++) {
floatVals[i] = DatumGetFloat8(valsContent[i]);
}
break;
default:
ereport(ERROR, (errmsg("Mode subject must be SMALLINT, INTEGER, BIGINT, REAL, or DOUBLE PRECISION values")));
break;
}
// Count how many distinct values there are:
for (i = 0, j = 1; i < valsLength - 1; i++, j += (floatVals[i] != floatVals[i + 1]));
counts = palloc0(sizeof(valcount) * j);
counts[0].value = floatVals[0];
counts[0].count = 1;
// Generate counts for each distinct value:
for (i = j = 0; i < valsLength - 1; i++, counts[j].count++) {
if (floatVals[i] != floatVals[i + 1]) counts[++j].value = floatVals[i + 1];
}
qsort(counts, j + 1, sizeof(valcount), compare_valcount);
for (i = 0; i <= j && counts[i].count == counts[0].count; i++);
// Now i has the number of the winners.
// Average all the winners:
v = counts[0].value;
for (j = 1; j < i; j++) {
v += (counts[j].value - v) / (j + 1);
}
PG_RETURN_FLOAT8(v);
}