Commits
Uwe L. Korn authored and Wes McKinney committed 4440e4011d8
ARROW-543: C++: Lazily computed null_counts counts number of non-null entries Author: Uwe L. Korn <uwelk@xhochy.com> Closes #329 from xhochy/ARROW-543 and squashes the following commits: 191792b [Uwe L. Korn] ARROW-543: C++: Lazily computed null_counts counts number of non-null entries