This function is strange. Looks like the implementation is of low quality.

```
bool isDeterministic() const override { return false; }
bool isDeterministicInScopeOfQuery() const override { return false; }
```
Why it is not deterministic? Missing a comment.

```
String convertToJson(const PODArray<String> & variant_names, const Variants & variants)
{
    FormatSettings settings;

    WriteBufferFromOwnString buf;

    writeCString("{\"data\":[", buf);
    for (size_t i = 0; i < variants.size(); ++i)
    {
        writeCString("{\"variant_name\":", buf);
        writeJSONString(variant_names[i], buf, settings);
        writeCString(",\"x\":", buf);
        writeText(variants[i].x, buf);
        writeCString(",\"y\":", buf);
        writeText(variants[i].y, buf);
        writeCString(",\"beats_control\":", buf);
        writeText(variants[i].beats_control, buf);
        writeCString(",\"to_be_best\":", buf);
        writeText(variants[i].best, buf);
        writeCString("}", buf);
        if (i != variant_names.size() -1)
            writeCString(",", buf);
    }
    writeCString("]}", buf);

    return buf.str();
}
```
It returns unstructured data? :scream: 

As first step we can remove documentation for this function.
CC @nikitamikhaylov 
#pragma once
#include <Common/config.h>
#if !defined(ARCADIA_BUILD) && USE_STATS
#    include <base/types.h>
#    include <Common/PODArray.h>
#    include <algorithm>
#    include <iostream>
#    include <vector>
namespace DB
{
struct Variant
{
    Float64 x;
    Float64 y;
    Float64 beats_control;
    Float64 best;
};
using Variants = PODArray<Variant>;
template <bool higher_is_better>
Variants bayesian_ab_test(String distribution, PODArray<Float64> & xs, PODArray<Float64> & ys);
String convertToJson(const PODArray<String> & variant_names, const Variants & variants);
}
#endif