ealry draft of model
use numpy style
instance should not have col_names
renamed arg
refactored mechanism of uni_col_names
added mapping's methods
draft of commit
handel the slice for proxy
clear commit mechanism
removed exit
renamed vars
added _pick
draft of commit v2
reduced the operations
added a todo
complete commit's function roughly
renamed class vars
refactoring
col-oriented model
modified the way of access elems