According to a recent study, machine learning algorithms are expected to replace 25% of the jobs across the world, in the next 10 years. With the rapid growth of big data and availability of programming tools like Python and R –machine learning is gaining mainstream presence for data scientists. Machine learning applications are highly automated and self-modifying which continue to improve over time with minimal human intervention as they learn with more data. For instance, Netflix’s recommendation algorithm learns more about the likes and dislikes of a viewer based on the shows every viewer watches. To address the complex nature of various real world data problems, specialized machine learning algorithms have been developed that solve these problems perfectly. For beginners who are struggling to understand the basics of machine learning, here is a brief discussion on the top machine learning algorithms used by data scientists.
Machine Learning algorithms are classified as –
Machine learning algorithms that make predictions on given set of samples. Supervised machine learning algorithm searches for patterns within the value labels assigned to data points.
There are no labels associated with data points. These machine learning algorithms organize the data into a group of clusters to describe its structure and make complex data look simple and organized for analysis.
These algorithms choose an action, based on each data point and later learn how good the decision was. Over time, the algorithm changes its strategy to learn better and achieve the best reward.
Common Machine Learning Algorithms Infographic
It would be difficult and practically impossible to classify a web page, a document, an email or any other lengthy text notes manually. This is where Naïve Bayes Classifier machine learning algorithm comes to the rescue. A classifier is a function that allocates a population’s element value from one of the available categories. For instance, Spam Filtering is a popular application of Naïve Bayes algorithm. Spam filter here, is a classifier that assigns a label “Spam” or “Not Spam” to all the emails.
Naïve Bayes Classifier is amongst the most popular learning method grouped by similarities, that works on the popular Bayes Theorem of Probability- to build machine learning models particularly for disease prediction and document classification. It is a simple classification of words based on Bayes Probability Theorem for subjective analysis of content.
Data Science Libraries in Python to implement Naïve Bayes – Sci-Kit Learn
K-means is a popularly used unsupervised machine learning algorithm for cluster analysis. K-Means is a non-deterministic and iterative method. The algorithm operates on a given data set through pre-defined number of clusters, k. The output of K Means algorithm is k clusters with input data partitioned among the clusters.
For instance, let’s consider K-Means Clustering for Wikipedia Search results. The search term “Jaguar” on Wikipedia will return all pages containing the word Jaguar which can refer to Jaguar as a Car, Jaguar as Mac OS version and Jaguar as an Animal. K Means clustering algorithm can be applied to group the webpages that talk about similar concepts. So, the algorithm will group all web pages that talk about Jaguar as an Animal into one cluster, Jaguar as a Car into another cluster and so on.
K Means Clustering algorithm is used by most of the search engines like Yahoo, Google to cluster web pages by similarity and identify the ‘relevance rate’ of search results. This helps search engines reduce the computational time for the users.
Data Science Libraries in Python to implement K-Means Clustering – SciPy, Sci-Kit Learn, Python Wrapper
Data Science Libraries in R to implement K-Means Clustering – stats
Support Vector Machine is a supervised machine learning algorithm for classification or regression problems where the dataset teaches SVM about the classes so that SVM can classify any new data. It works by classifying the data into different classes by finding a line (hyperplane) which separates the training data set into classes. As there are many such linear hyperplanes, SVM algorithm tries to maximize the distance between the various classes that are involved and this is referred as margin maximization. If the line that maximizes the distance between the classes is identified, the probability to generalize well to unseen data is increased.
SVM is commonly used for stock market forecasting by various financial institutions. For instance, it can be used to compare the relative performance of the stocks when compared to performance of other stocks in the same sector. The relative comparison of stocks helps manage investment making decisions based on the classifications made by the SVM learning algorithm.
Data Science Libraries in Python to implement Support Vector Machine –SciKit Learn, PyML , SVMStruct Python , LIBSVM
Apriori algorithm is an unsupervised machine learning algorithm that generates association rules from a given data set. Association rule implies that if an item A occurs, then item B also occurs with a certain probability. Most of the association rules generated are in the IF_THEN format. For example, IF people buy an iPad THEN they also buy an iPad Case to protect it. For the algorithm to derive such conclusions, it first observes the number of people who bought an iPad case while purchasing an iPad. This way a ratio is derived like out of the 100 people who purchased an iPad, 85 people also purchased an iPad case.
Data Science Libraries in Python to implement Apriori Machine Learning Algorithm – There is a python implementation for Apriori in PyPi
Data Science Libraries in R to implement Apriori Machine Learning Algorithm – arules
Linear Regression algorithm shows the relationship between 2 variables and how the change in one variable impacts the other. The algorithm shows the impact on the dependent variable on changing the independent variable. The independent variables are referred as explanatory variables, as they explain the factors the impact the dependent variable. Dependent variable is often referred to as the factor of interest or predictor.
Linear Regression finds great use in business, for sales forecasting based on the trends. If a company observes steady increase in sales every month - a linear regression analysis of the monthly sales data helps the company forecast sales in upcoming months.
Linear Regression helps assess risk involved in insurance or financial domain. A health insurance company can do a linear regression analysis on the number of claims per customer against age. This analysis helps insurance companies find, that older customers tend to make more insurance claims. Such analysis results play a vital role in important business decisions and are made to account for risk.
Data Science Libraries in Python to implement Linear Regression – statsmodel and SciKit
Data Science Libraries in R to implement Linear Regression – stats
Explanations about the top machine learning algorithms will continue, as it is a work in progress. Stay tuned to our blog to learn more about the popular machine learning algorithms and their applications!!!
The name of this algorithm could be a little confusing in the sense that Logistic Regression machine learning algorithm is for classification tasks and not regression problems. The name ‘Regression’ here implies that a linear model is fit into the feature space. This algorithm applies a logistic function to a linear combination of features to predict the outcome of a categorical dependent variable based on predictor variables.
The odds or probabilities that describe the outcome of a single trial are modelled as a function of explanatory variables. Logistic regression algorithms helps estimate the probability of falling into a specific level of the categorical dependent variable based on the given predictor variables.
Just suppose that you want to predict if there will be a snowfall tomorrow in New York. Here the outcome of the prediction is not a continuous number because there will either be snowfall or no snowfall and hence linear regression cannot be applied. Here the outcome variable is one of the several categories and using logistic regression helps.
Let us consider a simple example where a cake manufacturer wants to find out if baking a cake at 160°C, 180°C and 200°C will produce a ‘hard’ or ‘soft’ variety of cake ( assuming the fact that the bakery sells both the varieties of cake with different names and prices). Logistic regression is a perfect fit in this scenario instead of other statistical techniques. For example, if the manufactures produces 2 cake batches wherein the first batch contains 20 cakes (of which 7 were hard and 13 were soft ) and the second batch of cake produced consisted of 80 cakes (of which 41 were hard and 39 were soft cakes). Here in this case if linear regression algorithm is used it will give equal importance both the batches of cakes regardless of the number of cakes in each batch. Applying a logistic regression algorithm will consider this factor and give the second batch of cakes more weightage than the first batch.
The Data Science libraries in Python language to implement Logistic Regression Machine Learning Algorithm is Sci-Kit Learn.
The Data Science libraries in R language to implement Logistic Regression Machine Learning Algorithm is stats package (glm () function)
You are making a weekend plan to visit the best restaurant in town as your parents are visiting but you are hesitant in making a decision on which restaurant to choose. Whenever you want to visit a restaurant you ask your friend Tyrion if he thinks you will like a particular place. To answer your question, Tyrion first has to find out, the kind of restaurants you like. You give him a list of restaurants that you have visited and tell him whether you liked each restaurant or not (giving a labelled training dataset). When you ask Tyrion that whether you will like a particular restaurant R or not, he asks you various questions like “Is “R” a roof top restaurant?” , “Does restaurant “R” serve Italian cuisine?”, “Does R have live music?”, “Is restaurant R open till midnight?” and so on. Tyrion asks you several informative questions to maximize the information gain and gives you YES or NO answer based on your answers to the questionnaire. Here Tyrion is a decision tree for your favourite restaurant preferences.
A decision tree is a graphical representation that makes use of branching methodology to exemplify all possible outcomes of a decision, based on certain conditions. In a decision tree, the internal node represents a test on the attribute, each branch of the tree represents the outcome of the test and the leaf node represents a particular class label i.e. the decision made after computing all of the attributes. The classification rules are represented through the path from root to the leaf node.
Classification Trees- These are considered as the default kind of decision trees used to separate a dataset into different classes, based on the response variable. These are generally used when the response variable is categorical in nature.
Regression Trees-When the response or target variable is continuous or numerical, regression trees are used. These are generally used in predictive type of problems when compared to classification.
Decision trees can also be classified into two types, based on the type of target variable- Continuous Variable Decision Trees and Binary Variable Decision Trees. It is the target variable that helps decide what kind of decision tree would be required for a particular problem.
The Data Science libraries in Python language to implement Decision Tree Machine Learning Algorithm are – SciPy and Sci-Kit Learn.
The Data Science libraries in R language to implement Decision Tree Machine Learning Algorithm is caret.
Let’s continue with the same example that we used in decision trees, to explain how Random Forest Machine Learning Algorithm works. Tyrion is a decision tree for your restaurant preferences. However, Tyrion being a human being does not always generalize your restaurant preferences with accuracy. To get more accurate restaurant recommendation, you ask a couple of your friends and decide to visit the restaurant R, if most of them say that you will like it. Instead of just asking Tyrion, you would like to ask Jon Snow, Sandor, Bronn and Bran who vote on whether you will like the restaurant R or not. This implies that you have built an ensemble classifier of decision trees - also known as a forest.
You don’t want all your friends to give you the same answer - so you provide each of your friends with slightly varying data. You are also not sure of your restaurant preferences and are in a dilemma.You told Tyrion that you like Open Roof Top restaurants but maybe, just because it was summer when you visited the restaurant you could have liked it then. You may not be a fan of the restaurant during the chilly winters. Thus, all your friends should not make use of the data point that you like open roof top restaurants, to make their recommendations for your restaurant preferences.
By providing your friends with slightly different data on your restaurant preferences, you make your friends ask you different questions at different times. In this case just by slightly altering your restaurant preferences, you are injecting randomness at model level (unlike randomness at data level in case of decision trees). Your group of friends now form a random forest of your restaurant preferences.
Random Forest is the go to machine learning algorithm that uses a bagging approach to create a bunch of decision trees with random subset of the data. A model is trained several times on random sample of the dataset to achieve good prediction performance from the random forest algorithm.In this ensemble learning method, the output of all the decision trees in the random forest, is combined to make the final prediction. The final prediction of the random forest algorithm is derived by polling the results of each decision tree or just by going with a prediction that appears the most times in the decision trees.
For instance, in the above example - if 5 friends decide that you will like restaurant R but only 2 friends decide that you will not like the restaurant then the final prediction is that, you will like restaurant R as majority always wins.
Data Science libraries in Python language to implement Random Forest Machine Learning Algorithm is Sci-Kit Learn.
Data Science libraries in R language to implement Random Forest Machine Learning Algorithm is randomForest.
Human brain has a highly complex and non-linear parallel computer which can organize the structural constituents i.e. the neurons interconnected in a complex manner between each other. Let us take a simple example of face recognition-whenever we meet a person, a person who is known to us can be easily recognized with his name or he works at XYZ place or based on his relationship with you. We may be knowing thousands of people, the task requires the human brain to immediately recognize the person (face recognition).Now, suppose instead of the human brain doing it, if a computer is asked to perform this task. It is not going to be an easy computation for the machine as it does not know the person. You have to teach the computer that there are images of different people. If you know 10,000 people then you have to feed all the 10,000 photographs into the computer. Now, whenever you meet a person you capture an image of the person and feed it to the computer. The computer matches this photograph with all the 10,000 photographs that you have already fed into the database. At the end of all the computations-it gives the result with the photograph that best resembles the person. This could take several hours or more depending on the number of images present in the database. The complexity of the task will increase with increase in the number of images in the database. However, a human brain can recognise it instantly.