使用熊猫加载时，更改csv文件中的值。 （试图了解博客上显示的代码）

Question

I wanted to understand the below code.

First these codes are taken from a blog that I currently read about google BERT.

https://medium.com/swlh/a-simple-guide-on-using-bert-for-text-classification-bbf041ac8d04

The dataset can be download in the blog or from the link above.

import pandas as pd
train_df = pd.read_csv('data/train.csv', header=None) 
test_df = pd.read_csv("data/test.csv", header=None)
train_df[0] = (train_df[0] == 2).astype(int) #This is the part that I do not understand. I thought this code "(train_df[0] == 2)" will find all the values with "2" but since they did not specify what it should be converted to then how can everything changed from 2 --> 0?
train_df.head()

Current results:

    0   1
0   1   Unfortunately, the frustration of being Dr. Go...
1   0   Been going to Dr. Goldberg for over 10 years. ...
2   1   I don't know what Dr. Goldberg was like before...
3   1   I'm writing this review to give you a heads up...
4   0   All the food is great here. But the best thing...

I just wanted to understand the usage of the code and why it could success so I do not have any expected results.

Answer 1

The below code checks if value is 2 or not and converts to int. if value is 2 ie it is True and it will be converted to 1. Otherwise it is False and it will be converted to 0.

int() turns the boolean into 1 (True) or 0 (False).

train_df[0] = (train_df[0] == 2).astype(int)

Answer 2

>>>t_df[0]
0    1
1    2
2    1
3    1
4    2
Name: 0, dtype: int64
>>>t_df[0]==2
0    False
1     True
2    False
3    False
4     True
Name: 0, dtype: bool
>>>(t_df[0]==2).astype(int)
0    0
1    1
2    0
3    0
4    1
Name: 0, dtype: int64

That code will compare with 2 ( ==2 ) and convert the bool(False, True) values to int (0,1) values ( .astype(int) )