My goal of a project is to correctly assign medications. I have a large catalog at my disposal for this purpose. However, the medications do not appear there in exactly the same spelling. Possibly additional information was added or possible parts of the prescription were abbreviated.
I was already able to implement a possible algorithm using the Levensthein distance (token_set_ratio).
Because of the sometimes long additional information this algorithm assigns wrong medications, I wanted to ask if there are better algorithms for comparing strings. For example, does it make sense to implement machine learning algorithms or NLP technology? This is a relatively new area for me. I would appreciate any ideas or inspiration.
This sounds like a classic Deduplication task. For example, have a look at dedupe. This tool lets you annotate training examples and learns when two items refer to the same thing. It can be used with as few as 10 training sanples and has an active learning approach implemented.
Related
I used machine learning to train depression related sentences. And it was LinearSVC that performed best. In addition to LinearSVC, I experimented with MultinomialNB and LogisticRegression, and I chose the model with the highest accuracy among the three. By the way, what I want to do is to be able to think in advance which model will fit, like ml_map provided by Scikit-learn. Where can I get this information? I searched a few papers, but couldn't find anything that contained more detailed information other than that SVM was suitable for text classification. How do I study to get prior knowledge like this ml_map?
How do I study to get prior knowledge like this ml_map?
Try to work with different example datasets on different data types by using different algorithms. There are hundreds to be explored. Once you get the good grasp of how they work, it will become more clear. And do not forget to try googling something like advantages of algorithm X, it helps a lot.
And here are my thoughts, I think I used to ask such questions before and I hope it can help if you are struggling: The more you work on different Machine Learning models for a specific problem, you will soon realize that data and feature engineering play the more important parts than the algorithms themselves. The road map provided by scikit-learn gives you a good view of what group of algorithms to use to deal with certain types of data and that is a good start. The boundaries between them, however, are rather subtle. In other words, one problem can be solved by different approaches depending on how you organize and engineer your data.
To sum it up, in order to achieve a good out-of-sample (i.e., good generalization) performance while solving a problem, it is mandatory to look at the training/testing process with different setting combinations and be mindful with your data (for example, answer this question: does it cover most samples in terms of distribution in the wild or just a portion of it?)
In the regression problem I'm working with, there are five independent columns and one dependent column. I cannot share the data set details directly due to privacy, but one of the independent variables is an ID field which is unique for each example.
I feel like I should not be using ID field in estimating the dependent variable. But this is just a gut feeling. I have no strong reason to do this.
What shall I do? Is there any way I decide which variables to use and which to ignore?
Well, I agree with #desertnaut. Id attribute does not seem relevant when creating a model and provides no help in prediction.
The term you are looking for is feature selection. Since it's a comprehensive section so I would just tell you the methods that are mostly used by data scientists.
As for regression problems you can try correlation heatmap to find the features that are highly correlated with the target.
sns.heatmap(df.corr())
There are several other ways too like PCA,using tree inbuilt feature selection methods to find the right features for your model.
You can also try James Phillips method. This approach is limited since model time complexity will increase linearly with the features. But in your case where you've only four features to compare you can try it out. You can compare the regression model trained with all the four features with the model trained with only three features by dropping one of the four features recursively. This would mean training four regression models and comparing them.
According to you, the ID variable is unique for each example. So the model won't be able to learn anything from this variable as with every example, you get a new ID and hence no general patterns to learn as every ID only occurs once.
Regarding feature elimination, it depends. If you have domain knowledge, based on that alone you can engineer/ remove features as needed. If you don't know much about the domain, you can try out some basic techniques like Backward Selection, Forward Selection, etc via Cross Validation to get the model with the best value of the metric that you're working with.
Suppose you're trying to use machine learning for a classification task like, let's say, looking at photographs of animals and distinguishing horses from zebras. This task would seem to be within the state of the art.
But if you take a bunch of labelled photographs and throw them at something like a neural network or support vector machine, what happens in practice is that zebras are so much rarer than horses that the system just ends up learning to say 'always a horse' because this is actually the way to minimize its error.
Minimal error that may be but it's also not a very useful result. What is the recommended way to tell the system 'I want the best guess at which photographs are zebras, even if this does create some false positives'? There doesn't seem to be a lot of discussion of this problem.
One of the things I usually do with imbalanced classes (or skewed data sets) is simply generate more data. I think this is the best approach. You could go out in the real world and gather more data of the imbalanced class (e.g. find more pictures of zebras). You could also generate more data by simply making copies or duplicating it with transformations (e.g. flip horizontally).
You could also pick a classifier that uses an alternate evaluation (performance) metric over the one usually used - accuracy. Look at precision/recall/F1 score.
Week 6 of Andrew Ng's ML course talks about this topic: link
Here is another good web page I found on handling imbalanced classes: link
With this type of unbalanced data problem, it is a good approach to learn patterns associated with each class as opposed to simply comparing classes - this can be done via unsupervised learning learning first (such as with autoencoders). A good article with this available at https://www.r-bloggers.com/autoencoders-and-anomaly-detection-with-machine-learning-in-fraud-analytics/amp/. Another suggestion - after running the classifier, the confusion matrix can be used to determine where additional data should be pursued (I.e. many zebra errors)
I want to program a robot which will sense obstacles and learn whether to cross over them or bypass around them.
Since my project, must be realized in week and a half period, I must use an online learning algorithm (GA or such would take a lot time to test because robot needs to try to cross over the obstacle in order to determine is it possible to cross).
I'm really new to online learning so I don't really know which online learning algorithm to use.
It would be a great help if someone could recommend me a few algorithms that would be the best for my problem and some link with examples wouldn't hurt.
Thanks!
I think you could start with A* (A-Star)
It's simple and robust, and widely used.
There are some nice tutorials on the web like this http://www.raywenderlich.com/4946/introduction-to-a-pathfinding
Online algorithm is just the one that can collect new data and update a model incrementally without re-training with full dataset (i.e. it may be used in online service that works all the time). What you are probably looking for is reinforcement learning.
RL itself is not a method, but rather general approach to the problem. Many concrete methods may be used with it. Neural networks have been proved to do well in this field (useful course). See, for example, this paper.
However, to create real robot being able to bypass obstacles you will need much then just knowing about neural networks. You will need to set up sensors carefully, preprocess data from them, work out your model and collect a dataset. Not sure it's possible to even learn it all in a week and a half.
I want to teach myself enough machine learning so that I can, to begin with, understand enough to put to use available open source ML frameworks that will allow me to do things like:
Go through the HTML source of pages
from a certain site and "understand"
which sections form the content,
which the advertisements and which
form the metadata ( neither the
content, nor the ads - for eg. -
TOC, author bio etc )
Go through the HTML source of pages
from disparate sites and "classify"
whether the site belongs to a
predefined category or not ( list of
categories will be supplied
beforhand )1.
... similar classification tasks on
text and pages.
As you can see, my immediate requirements are to do with classification on disparate data sources and large amounts of data.
As far as my limited understanding goes, taking the neural net approach will take a lot of training and maintainance than putting SVMs to use?
I understand that SVMs are well suited to ( binary ) classification tasks like mine, and open source framworks like libSVM are fairly mature?
In that case, what subjects and topics
does a computer science graduate need
to learn right now, so that the above
requirements can be solved, putting
these frameworks to use?
I would like to stay away from Java, is possible, and I have no language preferences otherwise. I am willing to learn and put in as much effort as I possibly can.
My intent is not to write code from scratch, but, to begin with putting the various frameworks available to use ( I do not know enough to decide which though ), and I should be able to fix things should they go wrong.
Recommendations from you on learning specific portions of statistics and probability theory is nothing unexpected from my side, so say that if required!
I will modify this question if needed, depending on all your suggestions and feedback.
"Understanding" in machine learn is the equivalent of having a model. The model can be for example a collection of support vectors, the layout and weights of a neural network, a decision tree, or more. Which of these methods work best really depends on the subject you're learning from and on the quality of your training data.
In your case, learning from a collection of HTML sites, you will like to preprocess the data first, this step is also called "feature extraction". That is, you extract information out of the page you're looking at. This is a difficult step, because it requires domain knowledge and you'll have to extract useful information, or otherwise your classifiers will not be able to make good distinctions. Feature extraction will give you a dataset (a matrix with features for each row) from which you'll be able to create your model.
Generally in machine learning it is advised to also keep a "test set" that you do not train your models with, but that you will use at the end to decide on what is the best method. It is of extreme importance that you keep the test set hidden until the very end of your modeling step! The test data basically gives you a hint on the "generalization error" that your model is making. Any model with enough complexity and learning time tends to learn exactly the information that you train it with. Machine learners say that the model "overfits" the training data. Such overfitted models seem to appear good, but this is just memorization.
While software support for preprocessing data is very sparse and highly domain dependent, as adam mentioned Weka is a good free tool for applying different methods once you have your dataset. I would recommend reading several books. Vladimir Vapnik wrote "The Nature of Statistical Learning Theory", he is the inventor of SVMs. You should get familiar with the process of modeling, so a book on machine learning is definitely very useful. I also hope that some of the terminology might be helpful to you in finding your way around.
Seems like a pretty complicated task to me; step 2, classification, is "easy" but step 1 seems like a structure learning task. You might want to simplify it to classification on parts of HTML trees, maybe preselected by some heuristic.
The most widely used general machine learning library (freely) available is probably WEKA. They have a book that introduces some ML concepts and covers how to use their software. Unfortunately for you, it is written entirely in Java.
I am not really a Python person, but it would surprise me if there aren't also a lot of tools available for it as well.
For text-based classification right now Naive Bayes, Decision Trees (J48 in particular I think), and SVM approaches are giving the best results. However they are each more suited for slightly different applications. Off the top of my head I'm not sure which would suit you the best. With a tool like WEKA you could try all three approaches with some example data without writing a line of code and see for yourself.
I tend to shy away from Neural Networks simply because they can get very very complicated quickly. Then again, I haven't tried a large project with them mostly because they have that reputation in academia.
Probability and statistics knowledge is only required if you are using probabilistic algorithms (like Naive Bayes). SVMs are generally not used in a probabilistic manner.
From the sound of it, you may want to invest in an actual pattern classification textbook or take a class on it in order to find exactly what you are looking for. For custom/non-standard data sets it can be tricky to get good results without having a survey of existing techniques.
It seems to me that you are now entering machine learning field, so I'd really like to suggest to have a look at this book: not only it provides a deep and vast overview on the most common machine learning approaches and algorithms (and their variations) but it also provides a very good set of exercises and scientific paper links. All of this is wrapped in an insightful language starred with a minimal and yet useful compendium about statistics and probability