Python Map List of Strings to Integer List

Question

Let\'s say I have a list

l = [\'michael\',\'michael\',\'alice\',\'carter\']

I want to map it to the following:

k = [1,1,2,3         


        

Answer 1

Have a look at ord, which gives the unicode number for a given character:

>>> letters = ['a','b','c','d','e','f','g']
>>> [ord(x) for x in letters]
[97, 98, 99, 100, 101, 102, 103]

So you could do ord(x)-96 to convert a-z to 1-26 (careful about upper case, etc).

l = ['a','b','a','c']
k = [ord(x)-96 for x in l] # [1,2,1,3]

Again, careful about upper case and non-alphabet characters.

Answer 2

The function is zip

E.g:

>>> l = ['a','b','a','c']
>>> k = [1,2,1,3]¨
>>> zip(l,k)
[('a', 1), ('b', 2), ('a', 1), ('c', 3)]

If you want to use the items of l as index, you want an dictionary:

>>> d = dict(zip(l,k))
>>> d
{'a': 1, 'c': 3, 'b': 2}
>>> d['a']
1
>>> d['c']
3
>>> 

Answer 3

In order to answer the edited question, i.e., to map the list of strings to unique integers, one has to first find the unique strings and then do 1-1 mapping of the strings to integers in the original list of strings. For example,

s = ['michael','michael','alice','carter']

then unique strings are {'michael','alice','carter'}. Now, convert these strings to integers by 1-1 mapping like {'michael','alice','carter'} =[1,2,3] using dictionary {'michael':1,'alice':2,'carter':3}. In the third step, loop through the original list of strings; search the string in the dictionary for the corresponding integer and replace the string by that integer.

s=['michael','michael','alice','carter']

mydict={}
i = 0
for item in s:
    if(i>0 and item in mydict):
        continue
    else:    
       i = i+1
       mydict[item] = i

k=[]
for item in s:
    k.append(mydict[item])

Output:

k=[1, 1, 2, 3]

Answer 4

If I'm reading you correctly, you want to take a list of characters and convert them to integers, with a being 1, b being 2, etc.

l = ['a','b','a','c']
k = [ord(x.upper()) - 64 for x in l]

Threw the upper() in there so it doesn't matter whether they're upper case or lower.

Answer 5

From your question it is not clear if you want to generate k based on l or both l and k are given.

If you are looking to create k based on l, @mathematical.coffee's answer should do.

If you want a map from items in l to k, obviously, your items in l should be unique.

See if this is what you were looking for

dict((l[index], k[index]) for index in range(len(l)))

Or else, if you are looking for tuples:

[(l[index], k[index]) for index in range(len(l))]

Answer 6

If you don't care about the order of the assigned ids, this works:

# create unique list of  names
unique_l = set(l)

# create mappings from names to id
name2id = {name: idx+1 for idx, name in enumerate(unique_l)}

# map initial list of names to ids
k = [name2id[name] for name in l]

Output:

[2, 2, 1, 3]