ClickHouse/dbms/include/DB/AggregateFunctions/QuantilesCommon.h
2016-06-07 11:23:15 +03:00

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#pragma once
#include <vector>
#include <DB/Core/Field.h>
#include <DB/Core/FieldVisitors.h>
namespace DB
{
/** Параметры разных функций quantilesSomething.
* - список уровней квантилей.
* Также необходимо вычислить массив индексов уровней, идущих по возрастанию.
*
* Пример: quantiles(0.5, 0.99, 0.95)(x).
* levels: 0.5, 0.99, 0.95
* levels_permutation: 0, 2, 1
*/
template <typename T> /// float или double
struct QuantileLevels
{
using Levels = std::vector<T>;
using Permutation = std::vector<size_t>;
Levels levels;
Permutation permutation; /// Индекс i-го по величине уровня в массиве levels.
size_t size() const { return levels.size(); }
void set(const Array & params)
{
if (params.empty())
throw Exception("Aggregate function quantiles requires at least one parameter.", ErrorCodes::NUMBER_OF_ARGUMENTS_DOESNT_MATCH);
size_t size = params.size();
levels.resize(size);
permutation.resize(size);
for (size_t i = 0; i < size; ++i)
{
levels[i] = apply_visitor(FieldVisitorConvertToNumber<Float64>(), params[i]);
permutation[i] = i;
}
std::sort(permutation.begin(), permutation.end(), [this] (size_t a, size_t b) { return levels[a] < levels[b]; });
}
};
}