std::string block_shuffle(const std::string &s);

    for (int i = static_cast<int>(s.length()) - 1; i >= 0; --i)

    if (s.find(',') == std::string::npos)

        if (!freq[ s[i] ])
            s.erase( i, 1 );

        for (int i = static_cast<int>(s.length()) - 1; i >= 0; --i)
        {
            if (!freq[ s[i] ])
                s.erase( i, 1 );
        }
    }
    else
    {
        s = replace_all_of(s, " \t", "");

}
std::string map_lines::block_shuffle(const std::string &s)
{
    std::vector<std::string> segs = split_string(",", s);
    unsigned seglen = 0;
    std::vector<std::string> shuffled;
    for (int i = 0, size = segs.size(); i < size; ++i)
    {
        const int sel = random2(segs.size());
        
        shuffled.push_back( segs[ sel ] );
        segs.erase( segs.begin() + sel );
        
        if (!seglen)
            seglen = shuffled[i].length();
        else if (seglen != shuffled[i].length())
        {
            mprf(MSGCH_DIAGNOSTICS, "Bad shuffle parameter: %s", s.c_str());
            return ("");
        }
    }
    return comma_separated_line(shuffled.begin(), shuffled.end(), ",", ",");

    if (s.find(',') != std::string::npos)
        return block_shuffle(s);

    if (toshuffle.empty() || shuffled.empty())
        return;