import re

# Convert product reviews to a string
text = pd.Series.to_string(data['text'], index = False)

# Remove newline characters
text = re.sub('n', '', text)

# Calculate sum of numbers, letters, and spaces
numbers = sum(c.isdigit() for c in text)
letters = sum(c.isalpha() for c in text)
spaces  = sum(c.isspace() for c in text)
others  = len(text) - numbers - letters - spaces