Ordering of components following transformation in Principal Component Analysis

I have been utilizing the PCA class from sklearn.decomposition to reduce the dimensionality of my feature space for visualization purposes.

I have a question about the outcome: Upon implementing the fit and transform functions of the PCA class, I receive an array named X_transformed with shape (n_samples, n_components), as mentioned in the documentation. Is the order of columns in the X_transformed array sorted by the amount of variance explained? The documentation notes that PCA.components_ is ordered by explained variance, so I assume that the columns in X_transformed follow suit. Please correct me if I am mistaken.

Here's a quick example:

from sklearn.decomposition import PCA

pca = PCA()
pca.fit(X) # X represents an array containing my original features. X.shape=(n_samples, n_features)
X_transformed = pca.transfom(X) # Now, does the order of columns in X_transformed indicate explained variance?

Thank you!

Answer №1

Just had a brilliant idea to experiment with

from sklearn.decomposition import PCA
import numpy as np


pca_2 = PCA(n_components=2)
X_transformed_2 = pca_2.fit_transform(X)
# X_transformed_2 contains two components that explain the most variance

pca_10 = PCA(n_components=10)
X_transformed_10 = pca_10.fit_transform(X)
# X_transformed_10 contains 10 components that explain the most variance


# Theory: If we arrange the first 2 components in X_transformed_10 based on explained variance, they should match X_transformed_2
np.array_equal(X_transformed_2, X_transformed_10[:, 2]) ## will output True

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