Checking if starting digits are similar in list in Python

Sometimes in a given Python list we may be interested only in the first digit of each element in the list. In this article we will check if the first digit of all the elements in a list are same or not.

Using set() with map()

Set in Python does not allow any duplicate values in it. So we take the first digit of every element and put it in a set. If all the digits are same then the length of the set will be only 1 as no duplicates are allowed.

Example

numbers = [63, 652, 611, 60]

# Given list
print("Given list:", numbers)

# Using set and map
if len(set(x[0] for x in map(str, numbers))) == 1:
    print("All elements have same first digit")
else:
    print("Not all elements have same first digit")

The output of the above code is ?

Given list: [63, 652, 611, 60]
All elements have same first digit

Using all() Function

In this approach we take the first digit of the first element and compare it with the first digit of all the elements. If all of them are equal, then we say all the elements have same first digit.

Example

numbers = [63, 652, 611, 70]

# Given list
print("Given list:", numbers)

# Using all() function
if all(str(i)[0] == str(numbers[0])[0] for i in numbers):
    print("All elements have same first digit")
else:
    print("Not all elements have same first digit")

The output of the above code is ?

Given list: [63, 652, 611, 70]
Not all elements have same first digit

Using String Slicing Method

We can also extract the first digit by converting numbers to strings and using slicing to get the first character.

Example

numbers = [123, 145, 167, 189]

# Given list
print("Given list:", numbers)

# Get first digits using string slicing
first_digits = [str(num)[0] for num in numbers]
print("First digits:", first_digits)

# Check if all first digits are same
if len(set(first_digits)) == 1:
    print("All elements have same first digit")
else:
    print("Not all elements have same first digit")

The output of the above code is ?

Given list: [123, 145, 167, 189]
First digits: ['1', '1', '1', '1']
All elements have same first digit

Comparison

Conclusion

Use the all() function approach for the most efficient solution as it stops checking once a mismatch is found. The set() method provides a compact one-liner, while string slicing offers the clearest step-by-step approach.