/*!
* \param i The ith occurrence. \f$i\in [1..rank(size(),c)]\f$.
* \param c The symbol c.
* \par Time complexity
* \f$ \Order{H_0} \f$ on average, where \f$ H_0 \f$ is the zero order
* entropy of the sequence
*/
size_type select(size_type i, value_type c)const {
assert(i > 0);
assert(i <= rank(size(), c));
size_type c_runs = m_bf_rank(m_C[c]+i) - m_C_bf_rank[c];
size_type offset = m_C[c] + i - 1 - m_bf_select(c_runs + m_C_bf_rank[c]);
return m_bl_select(m_wt.select(c_runs, c)+1) + offset;
};
