messy scatter plot regression line: Python

Question

In python 2.7.6, matlablib, scikit learn 0.17.0, When I make a polynomial regression lines on a scatter plot, the polynomial curve will be really messy like this:

Answer 1

While the plot is now correct, you messed up the pairing of X_test1 to y_test1 while sorting because you forgot to also sort y_test1 in the same way. The best solution is to sort right after the split. Then y_plot, which is computed later, will be automatically correct: (Here untested example using numpy as np)

X_train1, X_test1, y_train1, y_test1 =             train_test_split(LSTAT,MEDV,test_size=0.3,random_state=1)

sorted_index = np.argsort(X_test1)
X_test1 = X_test1[sorted_index]
y_test1 = y_test1[sorted_index]