which model should I choose for this question - machine-learning

For example, the problem is: Whether I should buy this laptop or not? (Note that the question is not whether I will buy or not)
I'm new to machine learning and data science, I think I know the basic concept of this question, it's a supervised classification problem, but it's about should or should not, I'm confused if I should use decision tree or other models, many thanks.

Yes, you can treat it as a classification problem. You can start with collecting the data to train the algorithm and see if you can pick out some more features by looking at the patterns.

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Transfer Learning for small datasets of structured data

I am looking to implement machine learning for a problems that are built on small data sets related to approvals of expenses in a specific supply chain domain. Typically labelled data is unavailable
I was looking to build models in one data set that I have labelled data and then use that model developed in similar contexts- where the feature set is very similar, but not identical. The expectation is that this allows the starting point for recommendations and gather labelled data in the new context.
I understand this is the essence of Transfer Learning. Most of the examples I read in this domain speak of image data sets- any guidance how this can be leveraged in small data sets using standard tree-based classification algorithms
I can’t really speak to tree-based algos, I don’t know how to do transfer learning with them. But, for deep learning models, the customary method for transfer learning is to load up a pretrained model, then retrain the last layer of the dataset using your new data, and then fine-tune the rest of the network.
If you don’t have much data to go on, you might look into creating synthetic data.
raghu, I believe you are looking for a kernel method when you are saying abstraction layer in deep learning. There are several ML algorithms that support kernel functions. With kernel functions, you might be able to do it; but using kernel functions might be more complex than solving your original problem. I would lean toward Tdoggo's suggestion of using Decision Tree.
Sorry, I want to add a comment, but they won't allow me, so I posted a new answer.
Ok with tree-based algos you can do just what you said: train the tree on one dataset and apply it to another similar dataset. All you would need to do is change the terms/nodes on the second tree.
For instance, let’s say you have a decision tree trained for filtering expenses for a construction company. You will outright deny any reimbursements for workboots, because workers should provide those themselves.
You want to use the trained tree on your accounting firm, and so instead of workboots, you change that term to laptops, because accountants should be buying their own.
Does that make sense, and is that helpful to you?
After some research, we have decided to proceed with random forest models with the intuition that trees in the original model that have common features will form the starting point for decisions.
As we gain more labelled data in the new context, we will start replacing the original trees with new trees that comprise of (a)only new features and (b) combination of old and new features
This has worked to provide reasonable results in initial trials

Explaining how exactly Machine learning determine the result

Is it possible to somehow reverse the process or based on the model explain how ML model predicted the result?
Example: A bank uses ML for determining the interest rate of a loan for each person. How can I identify based on what data the ML decided the interest rate? For example the ML might discriminate someone (based on wrong data used in training), is there a way to find the problem, find how exactly the ML decided in each case?
This depends on the ML model you are using. Some models tend to be more complicated than others to understand.
The easiest rule-based model that explains the selection rules is a decision tree. You can use Weka for example to create such a tree and later view the branches that lead to each decision.

Is there any model/classifier that works best for NLP based projects like this?

I've written a program to analyze a given piece of text from a website and make conclusory classifications as to its validity. The code basically vectorizes the description (taken from the HTML of a given webpage in real-time) and takes in a few inputs from that as features to make its decisions. There are some more features like the domain of the website and some keywords I've explicitly counted.
The highest accuracy I've been able to achieve is with a RandomForestClassifier, (>90%). I'm not sure what I can do to make this accuracy better except incorporating a more sophisticated model. I tried using an MLP but for no set of hyperparameters does it seem to exceed the previous accuracy. I have around 2000 data points available for training.
Is there any classifier that works best for such projects? Does anyone have any suggestions as to how I can bring about improvements? (If anything needs to be elaborated, I'll do so.)
Any suggestions on how I can improve on this project in general? Should I include the text on a webpage as well? How should I do so? I tried going through a few sites, but the next doesn't seem to be contained in any specific element whereas the description is easy to obtain from the HTML. Any help?
What else can I take as features? If anyone could suggest any creative ideas, I'd really appreciate it.
You can search with keyword NLP. The task you are facing is a hot topic among those study deep learning, and is called natural language processing.
RandomForest is a machine learning algorithm, and probably works quite well. Using other machine learning algorithms might improve your accuracy, or maybe not. If you want to try out other machine learning algorithms that are light, it's fine.
Deep Learning most likely will outperform your current model, and starting with keyword NLP, you'll find out many models, hopefully Word2Vec, Bert, and so on. You can find out all the codes on github.
One tip for you, is to think carefully whether you can train the model or not. Trying to train BERT from scratch is a crazy thing to do for a starter, even for an expert. Try to bring pretrained model and finetune it, or just bring the word vectors.
I hope that this works out.

What kind of Machine learning category does this fall under?

My problem statement is this: The user is facing a problem. The user inputs a basic description of the problem Based on keywords in the input by user, the program would ask more specific questions to find out more about the problem. Then based on that, the program would ask questions more specific to the keywords provided in the second answer.
In the end the program will be able to produce a detailed description of the problem that the user is facing.
My question is that I am trying to do this via machine learning and what to know what category this falls under.
Is it Neural networks or supervised or unsupervised or completely something else?
Sounds like that this is related to Natural Language Processing (NLP). It is a category that deals with text understanding and human-computer interaction using natural languages. There exists both deep learning methods that uses neural networks in addition to some statistical methods. Your task is similar to a Chatbot I guess. With a quick search I found this:
https://uxplanet.org/nlp-vs-ci-who-is-the-king-of-chatbot-2f9d2e09f085. Hope this helps.
The question is not very clear. But, I am trying to give answer based on my understanding.
My general guess is that, you are talking about a chatbot which try to generate a problem description by continuing conversation with an user. It falls under the category of natural language processing (NLP).
Q. Is it Neural networks or supervised or unsupervised or completely something else?
It depends on how do you model your problem in terms of data. If you have data then you can formulate it as a supervised problem, and can use neural network to solve it.
But, I suspect you don't have the dataset for this particular task. In that case, you can look into many question-answer datasets. Otherwise, the problem can be solved in a algorithmic way too, in that case, no data is required.
As far as I can understand a user is interacting with a bot. If that is the case it is related to Natural Language Processing(NLP) as the data is in unstructured form i.e. text data. These type of data can be solved with either Supervised Learning or you can use Neural Network depending upon the complexity of the data and what is your objective.

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I am wanting some expert guidance here on what the best approach is for me to solve a problem. I have investigated some machine learning, neural networks, and stuff like that. I've investigated weka, some sort of baesian solution.. R.. several different things. I'm not sure how to really proceed, though. Here's my problem.
I have, or will have, a large collection of events.. eventually around 100,000 or so. Each event consists of several (30-50) independent variables, and 1 dependent variable that I care about. Some independent variables are more important than others in determining the dependent variable's value. And, these events are time relevant. Things that occur today are more important than events that occurred 10 years ago.
I'd like to be able to feed some sort of learning engine an event, and have it predict the dependent variable. Then, knowing the real answer for the dependent variable for this event (and all the events that have come along before), I'd like for that to train subsequent guesses.
Once I have an idea of what programming direction to go, I can do the research and figure out how to turn my idea into code. But my background is in parallel programming and not stuff like this, so I'd love to have some suggestions and guidance on this.
Thanks!
Edit: Here's a bit more detail about the problem that I'm trying to solve: It's a pricing problem. Let's say that I'm wanting to predict prices for a random comic book. Price is the only thing I care about. But there are lots of independent variables one could come up with. Is it a Superman comic, or a Hello Kitty comic. How old is it? What's the condition? etc etc. After training for a while, I want to be able to give it information about a comic book I might be considering, and have it give me a reasonable expected value for the comic book. OK. So comic books might be a bogus example. But you get the general idea. So far, from the answers, I'm doing some research on Support vector machines and Naive Bayes. Thanks for all of your help so far.
Sounds like you're a candidate for Support Vector Machines.
Go get libsvm. Read "A practical guide to SVM classification", which they distribute, and is short.
Basically, you're going to take your events, and format them like:
dv1 1:iv1_1 2:iv1_2 3:iv1_3 4:iv1_4 ...
dv2 1:iv2_1 2:iv2_2 3:iv2_3 4:iv2_4 ...
run it through their svm-scale utility, and then use their grid.py script to search for appropriate kernel parameters. The learning algorithm should be able to figure out differing importance of variables, though you might be able to weight things as well. If you think time will be useful, just add time as another independent variable (feature) for the training algorithm to use.
If libsvm can't quite get the accuracy you'd like, consider stepping up to SVMlight. Only ever so slightly harder to deal with, and a lot more options.
Bishop's Pattern Recognition and Machine Learning is probably the first textbook to look to for details on what libsvm and SVMlight are actually doing with your data.
If you have some classified data - a bunch of sample problems paired with their correct answers -, start by training some simple algorithms like K-Nearest-Neighbor and Perceptron and seeing if anything meaningful comes out of it. Don't bother trying to solve it optimally until you know if you can solve it simply or at all.
If you don't have any classified data, or not very much of it, start researching unsupervised learning algorithms.
It sounds like any kind of classifier should work for this problem: find the best class (your dependent variable) for an instance (your events). A simple starting point might be Naive Bayes classification.
This is definitely a machine learning problem. Weka is an excellent choice if you know Java and want a nice GPL lib where all you have to do is select the classifier and write some glue. R is probably not going to cut it for that many instances (events, as you termed it) because it's pretty slow. Furthermore, in R you still need to find or write machine learning libs, though this should be easy given that it's a statistical language.
If you believe that your features (independent variables) are conditionally independent (meaning, independent given the dependent variable), naive Bayes is the perfect classifier, as it is fast, interpretable, accurate and easy to implement. However, with 100,000 instances and only 30-50 features you can likely implement a fairly complex classification scheme that captures a lot of the dependency structure in your data. Your best bet would probably be a support vector machine (SMO in Weka) or a random forest (Yes, it's a silly name, but it helped random forest catch on.) If you want the advantage of easy interpretability of your classifier even at the expense of some accuracy, maybe a straight up J48 decision tree would work. I'd recommend against neural nets, as they're really slow and don't usually work any better in practice than SVMs and random forest.
The book Programming Collective Intelligence has a worked example with source code of a price predictor for laptops which would probably be a good starting point for you.
SVM's are often the best classifier available. It all depends on your problem and your data. For some problems other machine learning algorithms might be better. I have seen problems that neural networks (specifically recurrent neural networks) were better at solving. There is no right answer to this question since it is highly situationally dependent but I agree with dsimcha and Jay that SVM's are the right place to start.
I believe your problem is a regression problem, not a classification problem. The main difference: In classification we are trying to learn the value of a discrete variable, while in regression we are trying to learn the value of a continuous one. The techniques involved may be similar, but the details are different. Linear Regression is what most people try first. There are lots of other regression techniques, if linear regression doesn't do the trick.
You mentioned that you have 30-50 independent variables, and some are more important that the rest. So, assuming that you have historical data (or what we called a training set), you can use PCA (Principal Componenta Analysis) or other dimensionality reduction methods to reduce the number of independent variables. This step is of course optional. Depending on situations, you may get better results by keeping every variables, but add a weight to each one of them based on relevant they are. Here, PCA can help you to compute how "relevant" the variable is.
You also mentioned that events that are occured more recently should be more important. If that's the case, you can weight the recent event higher and the older event lower. Note that the importance of the event doesn't have to grow linearly accoding to time. It may makes more sense if it grow exponentially, so you can play with the numbers here. Or, if you are not lacking of training data, perhaps you can considered dropping off data that are too old.
Like Yuval F said, this does look more like a regression problem rather than a classification problem. Therefore, you can try SVR (Support Vector Regression), which is regression version of SVM (Support Vector Machine).
some other stuff you can try are:
Play around with how you scale the value range of your independent variables. Say, usually [-1...1] or [0...1]. But you can try other ranges to see if they help. Sometimes they do. Most of the time they don't.
If you suspect that there are "hidden" feature vector with a lower dimension, say N << 30 and it's non-linear in nature, you will need non-linear dimensionality reduction. You can read up on kernel PCA or more recently, manifold sculpting.
What you described is a classic classification problem. And in my opinion, why code fresh algorithms at all when you have a tool like Weka around. If I were you, I would run through a list of supervised learning algorithms (I don't completely understand whey people are suggesting unsupervised learning first when this is so clearly a classification problem) using 10-fold (or k-fold) cross validation, which is the default in Weka if I remember, and see what results you get! I would try:
-Neural Nets
-SVMs
-Decision Trees (this one worked really well for me when I was doing a similar problem)
-Boosting with Decision trees/stumps
-Anything else!
Weka makes things so easy and you really can get some useful information. I just took a machine learning class and I did exactly what you're trying to do with the algorithms above, so I know where you're at. For me the boosting with decision stumps worked amazingly well. (BTW, boosting is actually a meta-algorithm and can be applied to most supervised learning algs to usually enhance their results.)
A nice thing aobut using Decision Trees (if you use the ID3 or similar variety) is that it chooses the attributes to split on in order of how well they differientiate the data - in other words, which attributes determine the classification the quickest basically. So you can check out the tree after running the algorithm and see what attribute of a comic book most strongly determines the price - it should be the root of the tree.
Edit: I think Yuval is right, I wasn't paying attention to the problem of discretizing your price value for the classification. However, I don't know if regression is available in Weka, and you can still pretty easily apply classification techniques to this problem. You need to make classes of price values, as in, a number of ranges of prices for the comics, so that you can have a discrete number (like 1 through 10) that represents the price of the comic. Then you can easily run classification it.

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