You need to format the output of ps. grep will only pass the line or not.
(You can filter processes within ps itself, but let's assume you need to use grep.)
The -f parameter to ps includes a full set of columns. If you don't want that, look at the -o option, e.g.
ps -e -o pid,comm,pcpu
Is this what you wanted? Many other things can be done with ps.
Read man cpu
for all the details