Python Find Index of all Occurrences in List
List Comprehension
List comprehension offers a shorter syntax when you want to create a new list based on the values of an existing list.
- The number of occurrences of an element in a list can be calculated with the help of
list.count(<item>)
. - It takes the
item
to be counted as its argument and returns the total number of times that element appears in thelist
.
count()
The count()
method returns the number of occurrences of a substring in the given string.
Syntax
string.count(substring, start=..., end=...)
items = [1, 4, 7, 8, 2, 9, 2, 1, 1, 0, 4, 3] print(items.count(1)) # 3
Finding the index of items
<list>.index(<item>)
will return the index number of the first occurrence of an item passed in.
Find all Indices of Element in list Python
items = [7, 4, 1, 0, 2, 5] print(items.index(4)) # 1 print(items.index(10)) # ValueError: 10 is not in list
start
andend
indices can also be provided to narrow the search to a specific section of the list.
names = ["Adam", "Alice", "Ben", "Tom", "Sam", "Jane"] names.index("Adam") # 0 names.index("Ben", 2, 5) # 3
- You can use
enumerate()
in a loop in almost the same way that you use the original iterable object.
names = ["Adam", "Alice", "Ben", "Tom", "Sam", "Jane"] indices = [i for i, x in enumerate(names) if x == "Tom"] print(indices) # [3]
import numpy as np values = np.array([ 11,22,33,12,23,45,54,56,23,82,11 ]) print(np.where(values == 11)[0]) # [ 0 10 ]