Classification In Machine Learning: A Comprehensive Guide (2021)


Machine Learning statistics and classifications in ML-machine learning are used in supervised learning of the applications wherein the algorithm learns from the input data to make new classifications and observations.

  1. Classifications in Machine Learning?
  2. Classification Algorithms
  3. Classifier Evaluation
  4. Algorithm Selection
  5. What is MNIST?

1. Classifications in Machine Learning?

Both unstructured or structured data of any given dataset can be used in classification in machine learning for classification into label, target, categories etc. in a predictive modelling process that starts with the class prediction of the given datapoints and then approximating the task of the input variables mapping function to discrete variables as the output to identify the category/class of the new datapoints in space and class.

  • Classification Terminologies in Machine Learning:

Some terminology in classifications in ML-machine learning to get familiar with is that the algorithm is called the Classifier. The Classification Model can predict if the data falls into a category or class using input data that train the algorithm. A feature is the property observed and is measurable. Binary Classification states if the classification executed is false or true. If the sample is to be assigned to a specific target/ class or target/label, then Multi-Class and Multi-label Classification is used. Initialize is the process of classifier assigning to be used.

Train the classifier process uses the sci-kit-learn with each classifier to fit(X, y) method where the model trains X and trains the label y. It then predicts the target – using the predict(X) method for an unlabeled observation X and returns predicted label y. Evaluation of the classifier process is then affected for accuracy score, classification report, and so on. 

There are 2 types of learners in classification in machine learning

  • Lazy Learners – They store the training data till classification using the testing data when it appears and has larger predicting times. Ex: case-based reasoning, k-nearest neighbour types of classification in machine learning, etc.
  • Eager Learners – Eager learners are trained before being data for predictions. It works the entire space based on a single hypothesis and is very fast in making predictions. Ex: Naive Bayes, Decision Tree, Artificial Neural Networks and so on.

2. Classification Algorithms

Supervised learning classification in machine learning has uses in face detection, speech recognition, document classification, handwriting recognition, etc. The various classification algorithms in machine learning are discussed briefly below.

  • Logistic Regression uses independent variables input to predict the dependant outcome, which always is a dichotomous and quantitative variable. Ex: False/True. Though better than the nearest neighbour and binary classification algorithms, it is a supervised learning classification solution only when its output is a binary predictable variable since it assumes the independent predictors and that missing values are not present in the data. It is implemented in Python and used in Word classification, disease risk factor predictions, voting applications, weather prediction etc.
  • Naive Bayes Classifier has a Naive Bayes classification in machine learning algorithm and predicts the predictor’s independence meaning a particular class feature of an example of classification in machine learning is unrelated to other features, or if the features are dependent on each other, then it predicts outcome probability independently for each feature. The Naive Bayes Theorem model used with large data sets is simple and easy to make. It is implemented using the theorem. 

This classifier is very fast and requires lesser amounts of training data. It is used in spam filters, document classification, analysis of regression vs classification of sentiments etc.

  • Stochastic Gradient Descent is used for linear models, and when large data samples are input. It uses the derivative values and types of gradient descent to instantly calculate the updates while supporting classification penalties and functional losses. Its main disadvantage is that it scales sensitively and needs a large number of hyperparameters. It is implemented in Python and used in applications of classification in machine learning using the IoT, linear regression coefficients, and neural networks weighted approach etc.
  • K-Nearest Neighbor is a lazy learner and stores training data instances in n-dimensional spaceClassification takes place using each point’s k nearest neighbours’ votes forming a simple majority. The labelling process is supervised learning. Through simple, to use and implementable in Python, the algorithm suffers as its computation cost is high. It works well with large datasets and noisy data. It is used in video recognition, handwriting detection applications, image recognition etc. 
  • The decision Tree algorithm’s model has a decision tree-like structure and uses the if-then rules with mutually exclusive and equally exhaustive classifications to break down the data and associate it to the tree of increments. The sequential learning model uses the rules on the training data one by one and removes the tuples and rules. The process continues till termination using the root node and a top-down recursive conquer by the dividing method. It can handle numerical and categorical data and is implemented in Python/R. Requiring very little data training and preparation, the model creates complex tree structures that are susceptible to bot categorization, and even small changes affect the whole tree. It is used in pattern recognition, data exploration, financial option pricing etc.
  • Random Forest is made up of Random Decision Trees that use its individual trees’ mean regression values. It is an ensemble learning of meta-estimators that are fit onto the subsample datasets whose sizes equal the input data size. Then the averages are used for predictions. The main disadvantages here are over-fitting due to reduction, complex implementation, and slow predictions in real-time. It is used in automobile engine parts failure prediction, banking risk applications, performance scores etc.
  • Artificial Neural Networks have multiple layers of neurons and use vector inputs converted into the output using neural network classification non-linear functions applied to a layer and passed to subsequent layers. It is a feed-forward algorithm where the weights are passed to the next layer and are very adaptive as the weights can easily be tuned. It works with untrained and noisy data and needs continuous value outputs and inputs to perform efficiently. Its main disadvantage is interpretability and is used for colouring B7W images, handwriting analysis, Computer Vision applications etc.

3. Classifier Evaluation

Classifiers in machine learning are evaluated based on efficiency and accuracy. The important methods of classification in machine learning used for evaluation are discussed below.

  • The holdout method is popular for testing classifiers’ predictive power and divides the data set into two subsets, where 80% is used for training and 20% unseen data for testing against the trained datasets.
  • Cross-Validation methods are used for over-fitting issues where the K-fold cross-validation technique is used to check for over-fitting by randomly partitioning the dataset into k-equal-sized sunsets and using one for testing and the others for training progressing fold-by fold.
  • Classification Reports use a cancer_data dataset for classification reporting with accuracy, F1-score, precision, and recall.
  • Receiver operating characteristics- ROC Curve- compares visually for classification of models providing the rate relationship between the true/ false positive rates with the area under the curve being the model’s accuracy.

4. Algorithm Selection

The SVM- support vector machine classifier separates into categories represented by points in the entire training dataset space with as wide as possible gaps between them. Newer points can be added into space by predicting which space and category the points would lie in. It is very advantageous in high dimensional spaces and is memory efficient in its decision making. However, the method does not allow the algorithm to make the estimates of probability directly.

To evaluate the classifier and find the best model algorithm, one would take the following route.

  • Data is read.
  • Independent and dependent data sets are created based on the features.
  • Data is split into testing and training datasets.
  • The model is trained on several algorithms like SVM, Decision tree, KNN etc., and the classifier evaluated.
  • The most accurate classifier is chosen.

5. What is MNIST?

Here we can check which algorithm is best suited for classification in machine learning using the MNIST dataset. MNIST is a set of tiny handwritten images numbering 70,000. Each has its representative digit in it and approximately 784 features. Each feature, in turn, has a 28×28 pixel density. The task is to use the classifiers and MNIST to make a digit predictor.

Loading MNIST dataset: The dataset can be imported from the sklearn. datasets using the import command followed by the fetch most command and the print commands to get the output file.

To explore the dataset: One will have to import the files using the matplot and pyplot libraries. The next thing to do is set preferences for the target and specifies that the feature is a 28×28 pixels image. Now plot the image for its output.

Data Splitting: Since the data has 70,000 entries, one needs to split the data and consider the beginning 6000 images, set the test set for 1000 entries and use the shape of y and X to model the training data. 

Data Shuffling: One uses the NumPy array to shuffle the data, improve model efficiency and remove errors.

Using Logistic Regression, creating a Digit Predictor: This can be executed using the train commands before outputting the file. Now import the logistic regression linear model from sklearn where the clf is the Logistic Regression and output the file.

Cross-Validation: To do cross-validation, one uses the sklearn kit with the following commands to import the score and validation files which are then output. 

Creating A Predictor Using Support Vector Machine: Once more import, the svm file from sklearn is used to predict the digital predictor, and the file output is cross-validated. Thus one can create a digit predictor. Since the task was to predict from all data entries if the digit ‘two-2’ was present and the classifier’s output was false, accuracy was gained using cross-validation. The SVM classifier was not as accurate as of the logistic regression classifier.


We have studied various algorithms and classifiers used in classification in machine learning and how to create a digit predictor in the above article.

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