by_for:  undefined=2398233, defined=9601767
by_grep: undefined=2398233, defined=9601767
Benchmark: running byfor, bygrep for at least 300 CPU seconds...
     byfor: 311 wallclock secs (311.09 usr +  0.03 sys = 311.12 CPU) @  0.06/s (n=20)
    bygrep: 313 wallclock secs (312.95 usr +  0.04 sys = 312.99 CPU) @  0.04/s (n=13)
       s/iter bygrep  byfor
bygrep   24.1     --   -35%
byfor    15.6    55%     --