Write a program in Python to filter the elements in a series which contains a string start and endswith 'a'

In this tutorial, we'll learn how to filter elements in a Pandas Series that start and end with the same character. We'll explore different approaches to find strings that begin and end with 'a'.

Sample Input and Output

Input ? Assume, you have a Series:

0    apple
1    oranges
2    alpha
3    aroma
4    beta

Output ? The result for elements that start and end with 'a':

2    alpha
3    aroma

Using Regular Expression

The first approach uses regular expressions to match strings that start and end with 'a'. The pattern r'^[a]$|^([a]).*\1$' matches single 'a' or strings starting and ending with 'a'.

Example

import pandas as pd
import re

fruits = ["apple", "oranges", "alpha", "aroma", "beta"]
data = pd.Series(fruits)

# Regular expression pattern
exp = r'^[a]$|^([a]).*\1$'
matched_items = []

for item in data:
    if re.search(exp, item):
        matched_items.append(item)

result = data[data.isin(matched_items)]
print(result)

2    alpha
3    aroma
dtype: object

Using String Methods with Lambda

A simpler approach uses Python's built-in string methods startswith() and endswith() with the filter() function.

Example

import pandas as pd

fruits = ["apple", "oranges", "alpha", "aroma", "beta"]
data = pd.Series(fruits)

# Filter using lambda function
filtered_items = list(filter(lambda x: x.startswith('a') and x.endswith('a'), fruits))
result = data[data.isin(filtered_items)]
print(result)

2    alpha
3    aroma
dtype: object

Using Pandas String Accessor

The most Pythonic approach uses Pandas' built-in string accessor methods for efficient filtering.

Example

import pandas as pd

fruits = ["apple", "oranges", "alpha", "aroma", "beta"]
data = pd.Series(fruits)

# Using Pandas string methods
result = data[data.str.startswith('a') & data.str.endswith('a')]
print(result)

2    alpha
3    aroma
dtype: object

Comparison

Conclusion

The Pandas string accessor method (data.str.startswith() & data.str.endswith()) is the most efficient and readable approach. It's specifically designed for Series operations and offers better performance than regular expressions or lambda functions.