CODEWITHSUNDEEP
pythonlistelement
D. Forrester
D. Forrester

Reputation: 25

finding an element from one list in another list in python

Is there a way to have two lists named list1 and list2 and be able to look up the position of one entry in another. i.e.

list_one = ["0", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]

list_two = ["h","e","l","l","o"]

my aim is to allow the user to enter a word which the program will then convert in a set of numbers corresponding to the letters entries in list_one

so if the user did input hello the computer would return 85121215 (being the position of the entries)

is there a possible way to do this

Upvotes: 2

Views: 18699

Answers (5)

Dadep
Dadep

Reputation: 2788

you can iterate thought the list :

>>> for i in range(len(list_two)):
...     for j in range(len(list_one)):
...             if list_two[i]==list_one[j]:
...                     list_3.append(j)
>>> list_3
[8, 5, 12, 12, 15]

but wim's answer is more elegant !

Upvotes: 1

Simeon Aleksov
Simeon Aleksov

Reputation: 1335

Adding to @wim's answer, could be done with a simple comprehension.

>>> [list_one.index(x) for x in list_two]
[8, 5, 12, 12, 15]

Upvotes: 3

Jan
Jan

Reputation: 43169

Use .index() on a list:

list_one = ["0", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"]

string = "hello"
positions = [list_one.index(c) for c in string]
print(positions)
# [8, 5, 12, 12, 15]

Upvotes: 0

Eular
Eular

Reputation: 1807

the x.index(i) returns the position of the element i of the list x

print("".join([str(list_one.index(i)) for i in list_two]))
85121215

Upvotes: 0

wim
wim

Reputation: 362567

Looking up the position of an item in a list is not a very efficient operation. A dict is a better data structure for this kind of task. 

>>> d = {k:v for v,k in enumerate(list_one)}
>>> print(*(d[k] for k in list_two))
8 5 12 12 15

If your list_one is always just the alphabet, in alphabetical order, it's probably better and simpler to get something working by using the builtin function ord.

Upvotes: 9

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