import re


def string_to_onlyalpha(string):
    """
    Get only alphanumeric characters from a string.
    
    Replace hyphens with spaces so as to not mangle hyphenated words, and replace apostrophes with blanks to merge words like it's -> its, othewise we lose the ts.
    """
    string.replace("-", " ")
    string.replace("'", "")
    valids = re.sub(r"[^A-Za-z ]+", ' ', string)
    return valids.lower()