by_for:  undefined=2000300, defined=7999700
by_grep: undefined=2000300, defined=7999700
Benchmark: running for, grep for at least 5 CPU seconds...
       for:  5 wallclock secs ( 5.27 usr +  0.00 sys =  5.27 CPU) @ 163521.04/s (n=862318)
      grep:  6 wallclock secs ( 5.05 usr +  0.00 sys =  5.05 CPU) @ 224222.12/s (n=1131621)
         Rate  for grep
for  163521/s   -- -27%
grep 224222/s  37%   --