Linux-About sorting shell output

Linux-About sorting shell output

I have output from a customised log file like this:
8 24 yum
8 24 yum
8 24 make
8 24 make
8 24 cd
8 24 cd
8 25 make
8 25 make
8 25 make
8 26 yum
8 26 yum
8 26 make
8 27 yum
8 27 install
8 28 ./linux
8 28 yum
I'd like to know if there's anyway to count the number of specific values
of the third field. For example I may want to count the number of
"cd","yum","install","cat".
Thanks!