Ok, I know the title is not cool enough.. But hey, who knows maybe one day I will be couuuulll…
Ok now let’s talk about some fancy things which are not about me -what a shame-. At this point, I want to give a guarantee that if one day I become a best-seller of Medium this post will still here, I will not delete it.
Let’s be serious. Machine learning is a serious field. Unfortunately, I do not have any guess if they conquer the world someday. I will talk about some basic approaches of machine learning. After that, I will continue to explain as much as I can (not in this post. Clap for my honesty) with theory and some codes mainly on MATLAB and Python. Ok, let’s start.
KNNs are one of the most basic approaches of ML. Basically, they memorize all the data, and when a new data point comes they measure the distance of it to all memorized data after that the new data point classified into the same class with which most neighbors belong. Actually, Grammarly says I have 3 critical mistakes but I have a free plan so I don't know where are they damn I became nervous! Whatever, KNNs have a critical point which gives name to the approach K-neighbors. All results can change depending on this parameter. There is a figure in the following that explains KNNs in one figure.
As you can see in the figure, the purple triangle belongs to class1 (Blue triangles) if we choose 4 for the K parameter. There are many measuring approaches but mainly Euclidian, Minkowski, and Hamming are in use.
Now the most useful part. Advantages and disadvantages
- I am not sure if it is an advantage but I am totally sure it is not cool. There is no training time. As has been discussed above, KNNs just memorize the training data. So fast to train, slow to test.
- Easy to implement.
- All new data can be added to the model to enhance model performance.
- Not a good choice for big sets.
- Very sensitive to noise and missing data.
- All data must be normalized in the same way.
- Do not have a good performance on high dimension data.
Support Vector Machines (SVM)
Ok. Now things are getting more complicated. SVM is a very powerful method. Basically, SVM uses only the most challenging few data to optimize its parameters. These are called support vectors. Baaaaam! I added 2 figures to illustrate what is going on. In figure1 there is R² environment in figure 2 there is R³ environment. Ok! I know I lost you on the last sentence. So let's optimize it like that: If space is linearly separable then look at figure 1. If it is not then you should look at figure 2. In figure2 you see an example of kernel operations (I will talk about it in later posts). This is a very useful trick.
Basically, if data is not linearly separable you add a new dimension to data to find an optimum hyperplane. There are many kernels to make 2D data 3D. (Polynomial, radial, sigmoid etc.). We will talk about it in more detail in the next posts. Ok now take-home messages are ;
- Good performance on high-dimensional data
- Better performance on less data than other methods.
- Memory efficient
- It can be a rival to neural networks.
- It cannot be used as regressors.
- Bad naming. SVM hmmm… Can be better.. (My opinion)
Decision trees are the algorithm we all use in our daily lives. Unconsciously we all have this decision flow. Accept or not everybody has that spirit! Basically, decision trees are binary decisions optimized to input data.
- Easy to interpret.
- White box man! White box.
- Can be merged with other decision trees
- Very sensitive to changes in data
- Generally, accuracy is not adequate. So instead of decision trees, we use forests.
Ok that’s all folks. I will continue later. This was the first. My glasses steamed up, everybody at home cheering and I am out of coca-cola. I am starting a tradition which is finishing all posts with quotes from poets or authors I like.
As said by Turkish poet İsmet Özel: ‘İkna edilmişlerle yola çıkılmaz. Yola inanmışlarla çıkılır. İkna edilenler yola çıktığında ikna edilirler’ which means ‘You cannot start with the persuadeds. You start with believers. Those who are persuaded are persuaded when they start’.
I want to give references but I am not in the mooooood.