I don't understand how to fix the error. Why does it return type str?

Question

Python

Error on this line X_grid = np.arange(min(x),max(x),0.1)
"TypeError: unsupported operand type(s) for -: 'str' and 'str'"
source :

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

dataset = pd.read_csv('google.csv')
dataset.shape
dataset

dataset.plot(x = "Open", y = "High", alpha = 0.4)
plt.title(' Gogle Stock Trading')
plt.xlabel("Start Price")
plt.ylabel("Highest Price")
plt.xlim(60,100)
plt.ylim(60,100)
dataset.plot(x = "Open", y = " High", alpha = 0.9)
plt.title('Google Stock Trading')
plt.xlabel("Price at the start of the day")
plt.ylabel("Highest price")

x = pd.DataFrame(dataset.Open)
y = pd.DataFrame(dataset.High)

from sklearn.linear_model import LinearRegression
model = LinearRegression()
model.fit(x,y)

plt.scatter(x,y, color='red')
plt.plot(x, model.predict(x),color='green')
plt.title("Результат линейной регрессии")
plt.xlim(60,100)
plt.ylim(60,100)

from sklearn.preprocessing import PolynomialFeatures
poly_reg= PolynomialFeatures(degree=2)
x_poly = poly_reg.fit_transform(x)

lin_reg2 = LinearRegression()
lin_reg2.fit(x_poly,y)

X_grid = np.arange(min(x),max(x),0.1)
X_grid = X_grid.reshape(len(X_grid),1)
plt.scatter(x,y, color='red')

Answer 1

The problem is using min(x) on
x = pd.DataFrame(dataset.Open)
In this case, it will return the name of the column, i.e. line. To find the minimum for the data, you must explicitly specify which column to search for, i.e. min(x.Open)
Or initially do x not DataFrame, but Series
x = pd.Series(dataset.Open)
Then you can use min(x)