I have a csv file in which there are 10 columns. My project is to classify the reviews in my file as good or bad using nlp. When I do tokenisation of the column in which reviews is stored (review text column) using re.sub method it is giving an error called 'expected string or bytes like object'.

I have attached my csv file and also the code that i have tried in jupyter note book.

This is my [data file](https://drive.google.com/open?id=1m5yPYsvjBKYPFTqPrDayWgVLfzq6u_Ad).

My code is like this for now and the error is in the 're.sub' line

```
import numpy as np
import pandas as pd
import nltk
import matplotlib

dataset = pd.read_csv("C:/Users/a/Downloads/data.tsv", delimiter = "\t", quoting = 1)
dataset.head()

import re
import nltk
from nltk.corpus import stopwords
from nltk.stem.porter import PorterStemmer
corpus = []
for i in range(0, 1000):
  review = re.sub('[^a-zA-Z]', ' ', dataset['Review Text'][i])
  review = review.lower()
  review = review.split()
  ps = PorterStemmer()
  review = [ps.stem(word) for word in review if not word in 
  set(stopwords.words('english'))]
  review = ' '.join(review)
  corpus.append(review)

```

How do I correct my error? The next steps I want to do is vectorisation, training and classification.