Frequency Counter
Function Name: calculateFrequency
Description
Write a function that takes a string as its only parameter. Your function should return a mapping of each unique character to its frequency in the string. The frequency is defined as the number of times a character appears in the string. The function should ignore casing, meaning that 'a' and 'A' are considered the same character, and spaces and punctuation should be ignored. Your solution should not use any third-party libraries and should optimize for readability and efficiency.
Requirements
- The function must take exactly one parameter: the input string.
- The function should return a dictionary (or equivalent hashmap data structure) where the keys are the unique characters and the values are the counts of those characters in the string.
- Character comparison should be case-insensitive ('A' is the same as 'a').
- Ignore spaces, digits, and punctuation. Only alphabetic characters should be counted.
- The function should handle empty strings gracefully, returning an empty dictionary.
- Write at least three test cases for your function: one with a standard string, one with mixed casing and punctuation, and one that's an empty string.
Examples
For example, if the function is given the string 'Hello, world!', it should return {'h': 1, 'e': 1, 'l': 3, 'o': 2, 'w': 1, 'r': 1, 'd': 1}.Links
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