We present a data structure that stores a string $s[1..n]$ over the alphabet
$[1..\sigma]$ in $nH_0(s) + o(n)(H_0(s){+}1)$ bits, where $H_0(s)$ is the
zero-order entropy of $s$. This data structure supports the queries \access\
and \rank\ in time $\Oh{\lg\lg\sigma}$, and the \select\ query in constant
time. This result improves on previously known data structures using
$nH_0(s)+o(n\lg\sigma)$ bits, where on highly compressible instances the
redundancy $o(n\lg\sigma)$ cease to be negligible compared to the $nH_0(s)$
bits that encode the data. The technique is based on combining previous results
through an ingenious partitioning of the alphabet, and practical enough to be
implementable. It applies not only to strings, but also to several other
compact data structures. For example, we achieve $(i)$ faster search times and
lower redundancy for the smallest existing full-text self-index; $(ii)$
compressed permutations $\pi$ with times for $\pi()$ and $\pi^{-1}()$ improved
to log-logarithmic; and $(iii)$ the first compressed representation of dynamic
collections of disjoint sets.