CODEWITHSUNDEEP
pythonpython-3.xlistlist-comprehension
Kiran
Kiran

Reputation: 8538

How to access the next element from a unique list in Python

I have a list in Python

lst=['a', 'b', 'c', 'd', 'e', 'f']

What is the best way to access the next element in the list for a given value.

For instance I would like to get:

next_element(lst, 'c')
# 'd' should return adjacent value of 'c'

What is the Pythonian way of doing it?

Upvotes: 8

Views: 5951

Answers (4)

Justin
Justin

Reputation: 1031

You can use the next() built-in function:

    from itertools import islice

    some_list = ['a', 'b', 'c', 'd', 'e', 'f']
    item_value = "c"

    iterate_from = lambda some_list, item_value: next(islice(some_list, some_list.index(item_value) + 1, None))

    print(iterate_from(some_list, item_value))  # Output = d

The syntax of next() is:

next(iterator, default)
  1. iterator — next() retrieves next item from the iterator
  2. default (optional) — this value is returned if the iterator is exhausted (there is no next item)
  1. The next() function returns the next item from the iterator.
  2. If the iterator is exhausted, it returns the default value passed as an argument.
  3. If the default parameter is omitted and the iterator is exhausted, it raises StopIteration exception.

Upvotes: 3

Eliot Niedercorn
Eliot Niedercorn

Reputation: 1

One way to do it is to use a dictionary that maps the items of your list to integers, and then use the property of the modulo operation to ensure that you stay in the range of your list.

lst = ['a', 'b', 'c', 'd', 'e', 'f']
dict = {'a': 0, 'b': 1, 'c': 2, 'd': 3, 'e': 4, 'f': 5}

def next_element(item):
    corresponding_value = dict[item]
    next_value = (corresponding_value + 1) % len(lst)
    return lst[next_value]

print("The next element in the list after f is " + next_element("f"))

Will return "The next element in the list after f is a"

Upvotes: 0

Anderson-A
Anderson-A

Reputation: 74

Here is a simple way to do it

def next_element(l, elt):
    return l[l.index(elt)+1]

This will throw an error if the element passed into the function is the last one in the list. You might want to add some logic to handle that, depending on what you desire. Additionally, this assumes that all elements in the list are unique.

This solution however, will be very slow for a large list. list.index searches the list element by element until it finds the right elements, so it runs in O(n). If you are trying to walk through a list but don't want to use a loop, you can create an iterator to walk through the list as you need to.

lst = ['a', 'b', 'c', 'd', 'e', 'f']
myit = iter(lst)
next(myit) # will return 'a'
next(myit) # will return 'b'

Upvotes: 1

nsh1998
nsh1998

Reputation: 114

This function should do what you want it to - I think utilizing the index method would be the most pythonian way to solve your issue - although I could be wrong, this is just how I thought about it.

def next_element(lst, element):
   idx = lst.index(element)
   return lst[idx +1]

Upvotes: 2

Related Questions