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ML | Principal Component Analysis(PCA)
  • Last Updated : 07 Jul, 2018

Principal Component Analysis (PCA) is a statistical procedure that uses an orthogonal transformation which converts a set of correlated variables to a set of uncorrelated variables. PCA is a most widely used tool in exploratory data analysis and in machine learning for predictive models. Moreover, PCA is an unsupervised statistical technique used to examine the interrelations among a set of variables. It is also known as a general factor analysis where regression determines a line of best fit.

Module Needed:




import pandas as pd
import numpy as np
import matplotlib.pyplot as plt
import seaborn as sns
%matplotlib inline

Code #1:




# Here we are using inbuilt dataset of scikit learn
from sklearn.datasets import load_breast_cancer
  
# instantiating
cancer = load_breast_cancer()
  
# creating dataframe
df = pd.DataFrame(cancer['data'], columns = cancer['feature_names'])
  
# checking head of dataframe
df.head()

Output:
out
 
Code #2:




# Importing standardscalar module 
from sklearn.preprocessing import StandardScaler
  
scalar = StandardScaler()
  
# fitting
scalar.fit(df)
scaled_data = scalar.transform(df)
  
# Importing PCA
from sklearn.decomposition import PCA
  
# Let's say, components = 2
pca = PCA(n_components = 2)
pca.fit(scaled_data)
x_pca = pca.transform(scaled_data)
  
x_pca.shape

Output:
# Reduced to 569, 2
o1
 






# giving a larger plot
plt.figure(figsize =(8, 6))
  
plt.scatter(x_pca[:, 0], x_pca[:, 1], c = cancer['target'], cmap ='plasma')
  
# labeling x and y axes
plt.xlabel('First Principal Component')
plt.ylabel('Second Principal Component')

Output:
m
 




# components
pca.components_

Output:
out
 




df_comp = pd.DataFrame(pca.components_, columns = cancer['feature_names'])
  
plt.figure(figsize =(14, 6))
  
# plotting heatmap
sns.heatmap(df_comp)

Output:
out

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