OS X top command: sort by column

 After starting top, sort by column names by typing:

o<key>         Set primary sort key to : [+-]{command|cpu|pid
               |prt|reg|rprvt|rshrd|rsize|th|time|uid|username|vprvt
               |vsize}
O<skey>        Set secondary sort key to 

Field descriptions
command: command name
cpu: CPU usage
prt: number of Mach ports
reg: number of memory regions
rpvrt: resident (physical) private address space
rshrd: resident (physical) shared memory space
rsize: resident (physical) memory size
th: number of threads
time: execution time
uid: user ID
vprvt: private address space size
vsize: total virtual memory size