import streamlit as st
import numpy as np
import matplotlib.pyplot as plt

st.subheader("K nearest neighbor (KNN) classification")

st_col = st.columns(1)[0]

K = st.slider('Number of nearest neighbors (K)', min_value=1, max_value=10, value=5, step=1)

from sklearn.neighbors import KNeighborsClassifier as KNN
from sklearn.model_selection import cross_val_score

from sklearn.datasets import make_blobs
X, y = make_blobs(n_samples=1000, centers=3, n_features=2, cluster_std=6, random_state=42)
ntrain = 100

x_train = X[:ntrain]
y_train = y[:ntrain]
x_test = X[ntrain:]
y_test = y[ntrain:]

knn = KNN(n_neighbors=K)
knn.fit(x_train, y_train)
plt.figure()

x = np.linspace(np.min(x_test[:, 0]), np.max(x_test[:, 0]), 200)
y = np.linspace(np.min(x_test[:, 1]), np.max(x_test[:, 1]), 200)
xx, yy = np.meshgrid(x, y)
xy = np.c_[xx.ravel(), yy.ravel()]

y_predicted = knn.predict(xy)
#plt.pcolormesh(y_predicted.reshape(200, 200), cmap='jet')
plt.pcolormesh(xx, yy, y_predicted.reshape(200, 200), cmap='jet', alpha=0.2)
y_unique = np.unique(y_train)
markers = '*x+'
colors = 'bgr'
for i in range(len(y_unique)):
  plt.scatter(x_train[y_train == y_unique[i], 0],
               x_train[y_train == y_unique[i], 1],
               marker=markers[i],
               c=colors[i])
               

with st_col:
  st.pyplot(plt)
  
hide_streamlit_style = """
            <style>
            #MainMenu {visibility: hidden;}
            footer {visibility: hidden;}
            subheader {alignment: center;}
            </style>
            """
st.markdown(hide_streamlit_style, unsafe_allow_html=True) 

st.markdown("""
            There are several points to note on the effect of K on the quality of model fit:
            * Models with extremely small values of K learn the local patterns and do not generalize well thus they have a high variance or overfitting effect.
            * Models with extremely high values of K suffer from averaging effect over the entire space and thus do not do well even on the train points. This is known as a high bias or underfitting effect.
            """)