The function takes an input string and replaces each character as follows:
- If the character is a consonant, it is replaced by the next consonant.
- If the character is a vowel, it is replaced by the last consonant before it.
- If the character is a digit, it remains the same.

[CODE]:
```python
def approximated_function(s):
    vowels = "aeiou"
    output = []
    for c in s:
        if c.isdigit():
            output.append(c)
        elif c.lower() in vowels:
            last_consonant = chr(ord(c.lower()) - 1)
            output.append(last_consonant)
        else:
            next_consonant = chr(ord(c.lower()) + 1)
            output.append(next_consonant)
    return "".join(output)
```