RosettaCodeData/Task/Run-length-encoding/J/run-length-encoding-1.j

rle=: ;@(<@(":@(#-.1:),{.);.1~ 1, 2 ~:/\ ])
rld=: ;@(-.@e.&'0123456789' <@({:#~1{.@,~".@}:);.2 ])