Machine Learning strategy needed - machine-learning

I have a group of 20 yes/no/na questions that my company uses to assess whether or not to bid for an opportunity. To date, we have filled out the questionnaire 634 times.
The current algorithm simply divides yes / (yes + no) and a score over 50% recommends that we pursue the opportunity. n/a answers are disregarded.
We have tracked win/loss data on all of the pursuits, so I have a labeled dataset and I'm considering a supervised machine learning algorithm to replace our crude yes/no calculation.
I'm looking for a suggested method of supervised machine learning in Python (I'm most familar with SKLearn). Decision Tree Classifier?
Thank you in advance.

You have 20 y/n answers as features. Let yes be 1 and no be 0. So there are 20 binary features.
You also have target variable (win/loss) data. Let win be 1 and loss be 0. You can use an SVM/ NN right away. In my experience SVM and logistic regression give similar accuracies.
But if you are looking to explain each feature's contribution in shaping the decision, you should use naive-bayes or Decision Trees

It is important to know who is saying yeses and nos, so if you have 10 experts answering those 20 questions with yes/no/na, you have 10x20x3 states or binary features where every expert has 60 features.
Besides you can use features from the project itself like if the project is from oil industry or mining or manufacturing, etc. Some experts might be better in prediction in one industry over the others.
For classification, you can try random forests from sklearn.
Note that instead of classification (labelling if the project was pursued or disregarded) you can change the problem into a regression task by labelling the samples with the amount of profit or loss the company achieved from either pursuing (- or +) or disregarding (0) the project.
Hope this helps.

Related

Feature engineering gaussian distributed input

I am designing a NN classifier where most of the input features are estimations of gaussian distributions. I.e. one feature has a mu and a sigma value.
The classifier has about 30 input features, 60 if you consider each mu and sigma their own feature.
The number of outputs are 15, i.e. there are 15 possible classifications.
I have about 50k examples to use for training/verification.
I can think of a few different scenarios of how to transform these features into something useful but I am not clever enough to come to any conclusions on how they would impact my results.
First scenario is to just scale and blindly pass each mu and sigma individually. I don't really see how sigma would help the classifier in this case, since it's just a measure of uncertainty. Optimally this would lead to slightly "fuzzier" classifications which possibly could be used for estimating some certainty metric of a classification result.
Second scenario is to generate more test cases by drawing a value from the gaussian of each each of the 30 input features, and then normalizing these random values. This would give me more training data, which could be useful.
As I side note I have the possibility to get more data (about 50k examples more) but I am not sure how accurate that data is so I would like to try with this smaller set first to see if it converges.
The question is: Is there any consensus or interesting paper in the community, describing how to deal with estimated uncertainty in input features?
Thanks!
P.S. Sorry for my bad wording, ML is not my professional domain nor is English my native language.

How can I get the relative importance of features of a logistic regression for a particular prediction?

I am using a Logistic Regression (in scikit) for a binary classification problem, and am interested in being able to explain each individual prediction. To be more precise, I'm interested in predicting the probability of the positive class, and having a measure of the importance of each feature for that prediction.
Using the coefficients (Betas) as a measure of importance is generally a bad idea as answered here, but I'm yet to find a good alternative.
So far the best I have found are the following 3 options:
Monte Carlo Option: Fixing all other features, re-run the prediction replacing the feature we want to evaluate with random samples from the training set. Do this a large number of times. This would establish a baseline probability for the positive class. Then compare with the probability of the positive class of the original run. The difference is a measure of Importance of the feature.
"Leave-one-out" classifiers: To evaluate the importance of a feature, first create a model which uses all features, and then another that uses all features except the one being tested. Predict the new observation using both models. The difference between the two would be the importance of the feature.
Adjusted betas: Based on this answer, ranking the importance of the features by 'the magnitude of its coefficient times the standard deviation of the corresponding parameter in the data.'
All options (using betas, Monte Carlo and "Leave-one-out") seem like poor solutions to me.
The Monte Carlo is dependent on the distribution of the training set, and I cannot find any literature to support it.
The "leave one out" would be easily tricked by two correlated features (when one were absent, the other one would step in to compensate, and both would be given 0 importance).
The adjusted betas sounds plausible, but I cannot find any literature to support it.
Actual question: What is the best way to interpret the importance of each feature, at the moment of a decision, with a linear classifier?
Quick note #1: for Random Forests this is trivial, we can simply use the prediction + bias decomposition, as explained beautifully in this blog post. The problem here is how to do something similar with linear classifiers such as Logistic Regression.
Quick note #2: there are a number of related questions on stackoverflow (1 2 3 4 5). I have not been able to find an answer to this specific question.
If you want the importance of the features for a particular decision, why not simulate the decision_function (Which is provided by scikit-learn, so you can test whether you get the same value) step by step? The decision function for linear classifiers is simply:
intercept_ + coef_[0]*feature[0] + coef_[1]*feature[1] + ...
The importance of a feature i is then just coef_[i]*feature[i]. Of course this is similar to looking at the magnitude of the coefficients, but since it is multiplied with the actual feature and it is also what happens under the hood it might be your best bet.
I suggest to use eli5 which already have similar things implemented.
For you question:
Actual question: What is the best way to interpret the importance of each feature, at the moment of a decision, with a linear classifier?
I would say the answer come the the function show_weights() from eli5.
Furthermore this can be implemented with many other classifiers.
For more info you can see this question in related question.

Machine learning: Which algorithm is used to identify relevant features in a training set?

I've got a problem where I've potentially got a huge number of features. Essentially a mountain of data points (for discussion let's say it's in the millions of features). I don't know what data points are useful and what are irrelevant to a given outcome (I guess 1% are relevant and 99% are irrelevant).
I do have the data points and the final outcome (a binary result). I'm interested in reducing the feature set so that I can identify the most useful set of data points to collect to train future classification algorithms.
My current data set is huge, and I can't generate as many training examples with the mountain of data as I could if I were to identify the relevant features, cut down how many data points I collect, and increase the number of training examples. I expect that I would get better classifiers with more training examples given fewer feature data points (while maintaining the relevant ones).
What machine learning algorithms should I focus on to, first,
identify the features that are relevant to the outcome?
From some reading I've done it seems like SVM provides weighting per feature that I can use to identify the most highly scored features. Can anyone confirm this? Expand on the explanation? Or should I be thinking along another line?
Feature weights in a linear model (logistic regression, naive Bayes, etc) can be thought of as measures of importance, provided your features are all on the same scale.
Your model can be combined with a regularizer for learning that penalises certain kinds of feature vectors (essentially folding feature selection into the classification problem). L1 regularized logistic regression sounds like it would be perfect for what you want.
Maybe you can use PCA or Maximum entropy algorithm in order to reduce the data set...
You can go for Chi-Square tests or Entropy depending on your data type. Supervized discretization highly reduces the size of your data in a smart way (take a look into Recursive Minimal Entropy Partitioning algorithm proposed by Fayyad & Irani).
If you work in R, the SIS package has a function that will do this for you.
If you want to do things the hard way, what you want to do is feature screening, a massive preliminary dimension reduction before you do feature selection and model selection from a sane-sized set of features. Figuring out what is the sane-size can be tricky, and I don't have a magic answer for that, but you can prioritize what order you'd want to include the features by
1) for each feature, split the data in two groups by the binary response
2) find the Komogorov-Smirnov statistic comparing the two sets
The features with the highest KS statistic are most useful in modeling.
There's a paper "out there" titled "A selctive overview of feature screening for ultrahigh-dimensional data" by Liu, Zhong, and Li, I'm sure a free copy is floating around the web somewhere.
4 years later I'm now halfway through a PhD in this field and I want to add that the definition of a feature is not always simple. In the case that your features are a single column in your dataset, the answers here apply quite well.
However, take the case of an image being processed by a convolutional neural network, for example, a feature is not one pixel of the input, rather it's much more conceptual than that. Here's a nice discussion for the case of images:
https://medium.com/#ageitgey/machine-learning-is-fun-part-3-deep-learning-and-convolutional-neural-networks-f40359318721

Machine Learning Algorithm selection

I am new in machine learning. My problem is to make a machine to select a university for the student according to his location and area of interest. i.e it should select the university in the same city as in the address of the student. I am confused in selection of the algorithm can I use Perceptron algorithm for this task.
There are no hard rules as to which machine learning algorithm is the best for which task. Your best bet is to try several and see which one achieves the best results. You can use the Weka toolkit, which implements a lot of different machine learning algorithms. And yes, you can use the perceptron algorithm for your problem -- but that is not to say that you would achieve good results with it.
From your description it sounds like the problem you're trying to solve doesn't really require machine learning. If all you want to do is match a student with the closest university that offers a course in the student's area of interest, you can do this without any learning.
I second the first remark that you probably don't need machine learning if the student has to live in the same area as the university. If you want to use an ML algorithm, maybe it would best to think about what data you would have to start with. The thing that comes to mind is a vector for a university that has certain subjects/areas for each feature. Then compute a distance from a vector which is like an ideal feature vector for the student. Minimize this distance.
The first and formost thing you need is a labeled dataset.
It sounds like the problem could be decomposed into a ML problem however you first need a set of positive and negative examples to train from.
How big is your dataset? What features do you have available? Once you answer these questions you can select an algorithm that bests fits the features of your data.
I would suggest using decision trees for this problem which resembles a set of if else rules. You can just take the location and area of interest of the student as conditions of if and else if statements and then suggest a university for him. Since its a direct mapping of inputs to outputs, rule based solution would work and there is no learning required here.
Maybe you can use a "recommender system"or a clustering approach , you can investigate more deeply the techniques like "collaborative filtering"(recommender system) or k-means(clustering) but again, as some people said, first you need data to learn from, and maybe your problem can be solved without ML.
Well, there is no straightforward and sure-shot answer to this question. The answer depends on many factors like the problem statement and the kind of output you want, type and size of the data, the available computational time, number of features, and observations in the data, to name a few.
Size of the training data
Accuracy and/or Interpretability of the output
Accuracy of a model means that the function predicts a response value for a given observation, which is close to the true response value for that observation. A highly interpretable algorithm (restrictive models like Linear Regression) means that one can easily understand how any individual predictor is associated with the response while the flexible models give higher accuracy at the cost of low interpretability.
Speed or Training time
Higher accuracy typically means higher training time. Also, algorithms require more time to train on large training data. In real-world applications, the choice of algorithm is driven by these two factors predominantly.
Algorithms like Naïve Bayes and Linear and Logistic regression are easy to implement and quick to run. Algorithms like SVM, which involve tuning of parameters, Neural networks with high convergence time, and random forests, need a lot of time to train the data.
Linearity
Many algorithms work on the assumption that classes can be separated by a straight line (or its higher-dimensional analog). Examples include logistic regression and support vector machines. Linear regression algorithms assume that data trends follow a straight line. If the data is linear, then these algorithms perform quite good.
Number of features
The dataset may have a large number of features that may not all be relevant and significant. For a certain type of data, such as genetics or textual, the number of features can be very large compared to the number of data points.

Ordinal classification packages and algorithms

I'm attempting to make a classifier that chooses a rating (1-5) for a item i. For each item i, I have a vector x containing about 40 different quantities pertaining to i. I also have a gold standard rating for each item. Based on some function of x, I want to train a classifier to give me a rating 1-5 that closely matches the gold standard.
Most of the information I've seen on classifiers deal with just binary decisions, while I have a rating decision. Are there common techniques or code libraries out there to deal with this sort of problem?
I agree with you that ML problems in which the response variable is on an ordinal scale
require special handling--'machine-mode' (i.e., returning a class label) seems insufficient
because the class labels ignore the relationship among the labels ("1st, 2nd, 3rd");
likewise, 'regression-mode' (i.e., treating the ordinal labels as floats, {1, 2, 3}) because
it ignores the metric distance between the response variables (e.g., 3 - 2 != 1).
R has (at least) several packages directed to ordinal regression. One of these is actually called Ordinal, but i haven't used it. I have used the Design Package in R for ordinal regression and i can certainly recommend it. Design contains a complete set of functions for solution, diagnostics, testing, and results presentation of ordinal regression problems via the Ordinal Logistic Model. Both Packages are available from CRAN) A step-by-step solution of an ordinal regression problem using the Design Package is presented on the UCLA Stats Site.
Also, i recently looked at a paper by a group at Yahoo working on ordinal classification using Support Vector Machines. I have not attempted to apply their technique.
Have you tried using Weka? It supports binary, numerical, and nominal attributes out of the box, the latter two of which might work well enough for your purposes.
Furthermore, it looks like one of the classifiers that's available is a meta-classifier called OrdinalClassClassifier.java, which is the result of this research:
Eibe Frank and Mark Hall, A simple approach to ordinal classification. In Proceedings of the 12th European Conference on Machine Learning, 2001, pp. 145-156.
If you don't need a pre-made approach, then these references (in addition to doug's note about the Yahoo SVM paper) might be useful:
W Chu and Z Ghahramani, Gaussian processes for ordinal regression. Journal of Machine Learning Research, 2006.
Wei Chu and S. Sathiya Keerthi, New approaches to support vector ordinal regression. In Proceedings of the 22nd international conference on Machine Learning, 2005, 145-152.
The problems that dough has raised are all valid. Let me add another one. You didn't say how you would like to measure the agreement between the classification and the "gold standard". You have to formulate the answer to that question as soon as possible, as this will have a huge impact on your next step. In my experience, the most problematic part of any (ok, not any, most) optimization task is the score function. Try asking yourself whether all errors equal? Does miss-classifying the "3" as being "4" has the same impact as classifying "4" as "3"? What about "1" vs "5". Can mistakenly missing one case have disastrous consequences (miss HIV diagnosis, activate pilot ejection in a plane)
The simplest way to measure the agreement between categorical classifiers is Cohen's Kappa. More complicated methods are described in the following links here, here, here, and here
Having said that, sometimes picking a solution that "just works", instead of "the right one" is faster and easier. If I were you I would pick a machine learning library (R, Weka, I personally love Orange) and see what I get. Only if you don't have reasonably good results with that, look for more complex solutions
If not interested in fancy statistics a one hidden layer back propagation neural network with 3 or 5 output nodes will probably do the trick if the training data is sufficiently large. Most NN classifiers try to minimize the mean squared error which is not always desired. Support Vector Machines mentioned earlier is a good alternative.
FANN is a good library for back propagation NNs, it also has some tools to assist in training of the network.
There are two packages in R that might help taming ordinal data
ordinalForest on CRAN
rpartScore on CRAN
I'm working on an OrdinalClassifier that is based on the sklearn framework (specifically the OVR multiclass classifier) and which works well with sklearn workflow such as pipelines, cross validation, and scoring.
Through testing, I'm finding that it performs very well vs. standard non-ordinal multiclass classification using SVC. And it gives much greater control over optimizing for precision and recall on the positive class (in my testing, I used sklearn's diabetes dataset and transformed the disease progression target(y) into a low, medium, high class label. Testing via cross validation is on my repo along with attribution. Scoring is based on weighted f1.
https://github.com/leeprevost/OrdinalClassifier

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