Feature Engineering for Machine Learning
The “art” of creating usable features from already existing data while keeping in mind the learning aim and the ML model being applied is known as feature engineering. Data must be transformed into forms that are more closely related to the underlying target that must be learned. When done correctly, feature engineering can increase the usefulness of your current data and enhance the effectiveness of your machine learning models. To attain the same degree of performance, though, you might need to create models that are far more complex if you use poor features.
Feature engineering is the process of modifying your data set, which includes adding, deleting, combining, and performing mutation, in order to enhance the training of your machine learning model and achieve improved accuracy and performance. A solid understanding of the business issues and the data sources at hand is the foundation for effective feature engineering.
Definition of Feature
Features in machine learning are distinct, independent variables that function as inputs to your system. In reality, models employ these features while generating predictions. Additionally, new features in machine learning can be created from existing features by employing the feature engineering method.
Examples of what can be referred to as characteristics of machine learning models include the following:
- A model for estimating the likelihood of disease in plants might include the following features: size, colour, type of plant, etc.
- The level of education, number of years of experience, experience working in the field, and other characteristics may be included in a model for determining the eligibility of a candidate for a job profile.
- Features for a model to forecast the size of pants of a person include age, gender, height, weight, etc.
Feature Engineering
Feature engineering is an ML method that uses data to generate new variables that are not present in the training set. It can generate new features for supervised as well as unsupervised learning, with the aim of streamlining and accelerating data transformations while simultaneously improving model precision. While working with ML models, feature engineering is essential. Unfavorable features will directly affect your model, irrespective of the framework or the data.
The process of identifying and organizing crucial features from raw/unprocessed data so that they serve the needs of the ML model is known as feature engineering. It can be compared to the art of choosing the crucial aspects and translating them into features that are precise and relevant and meet the requirements of the model.
The term “feature engineering” refers to a variety of data engineering approaches, including the choice of pertinent features, handling of missing data, data encoding, and normalization of the data.
It serves as one of the most important responsibilities and has a significant impact on how a model turns out. It is crucial to correctly engineer the features of the input data in order to guarantee that the algorithm selected can perform to its fullest potential.
The process of feature engineering includes the following:
- Analyzing data and fixing irregularities (such as incomplete, wrong, or anomalous data).
- Removing variables that have no impact on the behavior of the model.
- Deleting duplicate records, comparing records, and occasionally doing data normalization.
Need for feature engineering.
According to a Forbes survey, data scientists devote almost 80% of their time to preparing data.This is where feature engineering comes into play. The accuracy of ML model suffers greatly without this phase.
Exploratory analysis and data acquisition are typical first steps in machine learning. Next step is to clean up the data. In this step, value duplication is eliminated, and incorrect labels of classes and features are fixed.
The next step is feature engineering. Cross-validation is done on the prediction models using the results from feature engineering.
When given raw data, ML model is not aware of the significance of the features. It is speculating without knowing the right direction. In this situation, feature engineering serves as the compass.
The complexity of the algorithms decreases when there are relevant and meaningful features. The findings will still be correct even though the algorithm being used is not the best fit for the problem.
Feature engineering steps
The procedures involved in feature engineering can change depending on the data scientists and ML engineers involved. The majority of machine learning algorithms do, however, incorporate a few standard steps, which are as follows:
1. Data Preparation: This is the initial phase. This stage involves putting raw data that has been gathered from various sources into a format that can be used by the ML algorithm. The data preparation could involve data cleaning, data delivery, augmentation of data, data fusion, or loading.
2. Exploratory Analysis: Data scientists are the main users of exploratory analysis, also known as exploratory data analysis (EDA), which is a crucial stage in feature engineering. This process entails analysis, data investment, and a summary of the key data characteristics. To identify the best statistical method for data analysis, to choose the best features for the data, and to better comprehend how data sources are manipulated, several data visualisation approaches are utilised.
3. Benchmarking entails establishing a uniform baseline for accuracy in order to compare all the variables against this baseline. To make the model more predictable and lower its error rate, benchmarking is used.
Feature engineering methods
1. Imputation: Sometimes, the dataset is incomplete. The columns may not contain any values. The values that are absent are filled in using imputation.
Imputation would be performed most simply by entering a default value. Data in the column could be categorical. You could choose the most typical category.
The missing data in the training set must be filled up with a value that is as near to the original value as possible in order to make ML model produce accurate results. Statistical imputation can be used in this situation.
Some of the most popular methods for imputation include K-nearest neighbours (KNN), tree-based models, and linear models.
2. Handling outliers: An outlier is any observation that deviates significantly from the majority. The results are distorted, and the predictive models are affected. Finding outliers is the initial step in handling them.
To find the outliers, one can use z-scores, box plots, or Cook’s distance.
A better strategy for identifying outliers is to use visualisations. It produces findings that are more accurate and makes it simpler to identify outliers.
The dataset can be cleaned up by removing the outliers. However, doing so also cuts down on the volume of training data. Note that when you have an abundance of observations, eliminating the outliers seems logical.
3. Grouping: There are various classes for each feature. There might not be many observations in some of these classes. We refer to these as sparse classes. The algorithm may produce a situation of data over-fitting as a result.
To develop a flexible model, overfitting, a major ML model issue, must be avoided. Such classes can be grouped to form new ones. To do this grouping, start by putting related classes together.
Grouping is also effective in other situations. Some features offer more information when combined than when used separately. They are known as interaction features.
For example, if a factory dataset has the sales data of milk with one column having total number of days milk sold and the second column containing the rate of milk to know the total sales, one needs to multiply these two features. Note that two features can be multiplied, added, subtracted, or divided.
4. Feature splitting: The opposite of feature interaction or grouping is feature split operation. As we have seen, two or more features are combined so as to perform grouping operations.
The goal of feature splitting is to obtain the required information by breaking one feature into two or more sections.
For example, if a column contains information on the price of an item in both rupees and paise format, but one is interested in knowing the price only in rupees, then splitting the price feature into two would be the best option.
The most frequent application of feature splitting is on features that include lengthy strings. These can be more easily understood and used by the machine learning algorithm if they are divided.
5. Log Transform: When the dataset distribution is not normal, then it is said to be a skewed dataset. A distorted/skewed dataset causes the model’s performance to be subpar.
In order to reduce the skewness and bring the model closer to normal, logarithmic transforms can be used.
Additionally, log transformation lessens the impact of outliers. In most datasets, outliers are a frequent occurrence. If you attempt to eliminate every outlier, you will wind up losing important data.
Removing outliers may not be the best option if your dataset is tiny.
The outliers are still present after log transformation, but their impact on the data is reduced. The data gets more robust as a result.
Note that this technique only functions for positive values. This means if your data contains negative numbers, then you must first add a constant to make the entire column positive before applying this technique.
6. Binning: Through binning, features with continuous values are converted to categorical features. One can sort these continuous values into a predetermined set of bins.
Continuous-valued features are converted to categorical features through binning. These continuous values can be divided into a predetermined number of bins.
This technique is used to strengthen the model and avoid overfitting of the data. But with binning, you ultimately lose information, and the model’s performance may suffer as a result.
Overfitting and enhanced performance must coexist in harmony.
The width of the bins may be permanent or adjustable. Fixed-width binning is adequate if the data is spread approximately equally. At the same time, adaptive binning performs better with irregular distribution of data.
Conclusion
In this article, we had the opportunity to explore feature engineering, its significance, its implementation steps, and various feature engineering methodologies.
We’ve seen feature engineering is a crucial and very beneficial method for data scientists that could significantly boost the effectiveness of ML models.