python - Giving indices to list entries -

i have python list looking this:

a1 = ['a','a','a','foo','c','d','a','e','bar','bar','bar','e','d','d'] 

i want transform this...

a2 = [1,1,1,2,3,4,1,5,6,6,6,5,4,4] 

...where entries in a1 taken in order , given incremental index in a2.

is there straight forward way in python?

one of ways of doing can be.

>>> a1 = ['a','a','a','foo','c','d','a','e','bar','bar','bar','e','d','d'] >>> ref = [] >>> in a1: ...    if not in ref: ...        ref.append(i) ...  >>> [ref.index(i)+1 in a1] [1, 1, 1, 2, 3, 4, 1, 5, 6, 6, 6, 5, 4, 4] 

logic

we remove duplicate values in original list (whilst preserving order). find index of individual items in list respect original list.

advantages

• simple concepts/ beginner level
• very straight forward.

disadvantages

• slow of order o(n²)