# Data Pre-processing with Data reduction techniques in Python

Data Reduction:

Data reduction means the reduction in certain aspects of data, typically the volume of data. The reduction can also be on other aspects such as the dimensionality of data when the data is multidimensional. Reduction in any aspect of data usually implies a reduction in the volume of data.

Dimensionality Reduction:

This reduces the size of data by encoding mechanisms. It can be lossy or lossless. If after reconstruction from compressed data, original data can be retrieved, such reductions are called lossless reduction else it is called lossy reduction. The two effective methods of dimensionality reduction are: Wavelet transforms and PCA (Principal Component Analysis).

Principal component analysis:

Principal Component Analysis, or PCA, is a dimensionality-reduction method that is often used to reduce the dimensionality of large data sets, by transforming a large set of variables into a smaller one that still contains most of the information in the large set.

Reducing the number of variables of a data set naturally comes at the expense of accuracy, but the trick in dimensionality reduction is to trade a little accuracy for simplicity. Because smaller data sets are easier to explore and visualize and make analyzing data much easier and faster for machine learning algorithms without extraneous variables to process.

So to sum up, the idea of PCA is simple — reduce the number of variables of a data set, while preserving as much information as possible.

PCA is sensitive to the relative scaling of the original variables.

PCA Projection to 2D

The explained variance tells you how much information (variance) can be attributed to each of the principal components. This is important as while you can convert 4-dimensional space to 2-dimensional space, you lose some of the variance (information) when you do this. By using the attribute explained_variance_ratio_, you can see that the first principal component contains 72.77% of the variance and the second principal component contains 23.03% of the variance. Together, the two components contain 95.80% of the information.

PCA Projection to 3D

The original data has 4 columns (sepal length, sepal width, petal length, and petal width). In this section, the code projects the original data which is 4 dimensional into 3 dimensions. The new components are just the three main dimensions of variation

Variance Threshold:

Variance Threshold is a simple baseline approach to feature selection. It removes all features whose variance doesn’t meet some threshold. By default, it removes all zero-variance features. Our dataset has no zero variance feature so our data isn’t affected here.

That is all about the data reduction techniques in Data Preprocessing.

For code visit the below link:

https://github.com/krunal43/App-Development/blob/main/Untitled8.ipynb