Get index of element occurrences in a list
You can use a Python list comprehension to build a new list containing the indices of all occurrences of a specific string in another list. Here’s a code sample: idx_lst = [ i for i, e in enumerate(my_lst) if (e == my_str) ].
#1 : Find index of an item in a list
Here’s a simple example of finding the index of a specific value in another Python list. Let’s start by defining a couple of simple lists we will use in this example:
prog_lang_lst = ['Java', 'Go', 'Python', 'C-sharp', 'R', 'JavaScript']
data_lang_lst = [ 'Python', 'R']
my_value = 'Python'Now we’ll use a list comprehension in order to build a new list containing the indices:
pos_idx_lst = [ i for i, e in enumerate(prog_lang_lst) if (my_elmnt == e)]
print(pos_idx_lst)
#this returns: [2]#2: Get the indices of multiple list elements with Python
We can use the same technique in order to print the indices of occurrences of multiple values in a list. Here are two simple ways to do this:
Option 1 – list comprehension:
pos_lst = [ i for i, e in enumerate(prog_lang_lst) if e in data_lang_lst]Option 2:
pos_lst = []
for i, e in enumerate (prog_lang_lst):
if e in data_lang_lst:
pos_lst.append (i)Both will return the following list:
[2, 4]
#3 : Count all occurrences of a value in a list?
What if we would like to count the number of occurrences of a specific string in a list? Here’s another simple snippet that delivers that.
prog_lang_lst = ['Python', 'Go', 'Python', 'C-sharp', 'R', 'JavaScript']
my_elmnt = 'Python'
print('The value {} appears {} times in the list.'.format(my_elmnt,prog_lang_lst.count(my_elmnt)))This will return:
The value Python appears 2 times in the list.
#4 : Select a specific list element by index
To choose a list value by its index – in this case the second element of our prog_lang_lst list, you use this simple syntax:
my_elmnt =prog_lang_lst[1]
print(my_elmnt)This will return: Go
Suggested follow up learning
How to divide a list of strings according to a specific condition?