My task is to calculate clashes between alert time schedule and the user calendar schedule to generate the clashes less alert time schedule.
How should i represent the chromosome according to this problem?
How should i represent the time slots? (Binary or Number)
Thank You
(Please Consider i'm a beginner to the genetic algorithm studies)
Questions would be: What have you tried so far? How good are your results so far? Also your Problem is
stated quite unspecific. Thus here is what I can give:
The Chromosome should probably be the starttime of the alerts in your schedule (if I understood your Problem correctly).
As important is to think of the ways you want to evaluate and calculate the Fitness of your individuals (here clashes (e.g. amount or time overlap between appointments), but it is obvious that you might find better heuristics to receive better solutions / faster convergence)
Binary or continuous number might both work: I am usually going for numbers whenever there is no strong reason to not do so (since it is easier to Interpret, debug, etc.). Binary comes with some nice opportunities with respect to Mutation and Recombination.
I strongly recommend playing around and reading about those Things. This might look like a lot of extra work to implement, but you should rather come to see them as hyperparameters which Need to be tuned in order to receive the best Outcome.
Related
I serve as internal auditor in few clients ,one of my client has thousands of employees in different location, most of them in the head office, the client looks for corporate control for the salary monitoring
is it make sense to use the regression method in order to find outliers,
potential parameter can be -years of experience, gender, level/rank etc
I planned to go over all the monthly payroll and look for significant outliers ,because of the differences between the global location, it might be a good idea to focus only in the head office
the idea is to train the model for previous months average and test it for the current month
what do you think is too much effort or theoretical ? or can have a good chance to bring value ?
thank you
This answers your question regarding the regression method to use. It makes sense to only use data from the head office, as adding data from different geographies will require you to add more data around general demographics, which you can avoid for a proof of concept.
Coming to the problem itself, you'll need to provide a better explanation of how you're defining outliers. Are you looking for mistakes in payroll? Or are you looking for people who make significantly more/less than their peers? You'll only be able to decide on a modelling framework once you get clarity the basic definitions.
Also, you might want to consider statistical significance tests like Grubbs test (more information on tests here) first, before moving to machine learning approaches. They're easier to set up and explain to non-practitioners.
I'm wondering how one goes about treating outliers at scale. Based on my experiences, I usually need to understand why there are outliers from the first place. What causes it, are there any patterns, or it just happens randomly. I know that, theoretically, we usually define outliers as data points outside of 3 standard deviation. But in the case where data is so big that you can't treat each feature one by one, and don't know if the 3 standard deviation rule is applicable anymore because of sparsity, how do we most effectively treat the outliers.
My intuition about high dimensional data is that data is sparse so the definition of "outliers" is harder to determine. Do you guys think we would be able to just get away with using ML algorithms that are more robust to outliers (tree based models, robust SVM, etc) instead of trying to treat outliers during preprocessing step? And if we really want to treat it, what is the best way to do it?
I would first propose a frame work for understanding the data. Imagine you are handed a dataset with no explanation of what it is. Analytics could actually be used to enable us to get understanding. Usually rows are observations and columns parameters of some sort regarding the observations. You first want to have a frame work for what you are trying to achieve. Now matter is going on, all data centers around the interest of people...that is why we decided to record it in some format. Given that, we are at most interested in:
1.) Object
2.) Attributes of object
3.) Behaviors of object
4.) Preferences of object
4.) Behaviors and preferences of object over time
5.) Relationships of object to other objects
6.) Affects of attributes, behaviors, preferences and other objects on object
So you are wanting to identify these items. So you open a data set and maybe you instantly recognize a time stamp. You then see some categorical variables and start doing relationship analysis for what is one to one, one to many, many to many. You then identify continuous variables. These all come together to give a foundation for identifying what is an outlier.
If we are evaluating objects of over time....is the rare event indicative of something that happens rarely, but we want to know about. Forest fire are outlier events...but they are events of great concern. If I am analyzing machine data and having rare events, but these rare events are tied to machine failure, then it matters. Basically.....does the rare event-parameter show evidence that it correlates to something that you care about?
Now if you have so many dimensions that the above approach is not feasible to your judgement, then you are seeking dimension reduction alternatives. I am currently employing Single Value Decomposition as at technique. I am already seeing situations where I am accomplishing the same level of predictive ability with 25% of the data. Which segways into my final thought; find a mark to decide whether the outliers matter or not.
Begin with leaving them in then begin your analysis, and run the work again with them removed. What were the affects. I believe that when you are in doubt, simply do both and see how different the results are. If there is little difference than maybe you are good to go. If there is significant difference of concern, then you are wanting to take an evidenced based approach of the outlier occurring. Simply because it is rare in your data does not mean it is rare. Think of certain type crimes that are under-reported (via arrest records). Lack of data showing politicians being arrested for insider trading does not mean that politicians are not doing insider trader en masse.
I am working on a machine learning scenario where the target variable is Duration of power outages.
The distribution of the target variable is severely skewed right (You can imagine most power outages occur and are over with fairly quick, but then there are many, many outliers that can last much longer) A lot of these power outages become less and less 'explainable' by data as the durations get longer and longer. They become more or less, 'unique outages', where events are occurring on site that are not necessarily 'typical' of other outages nor is data recorded on the specifics of those events outside of what's already available for all other 'typical' outages.
This causes a problem when creating models. This unexplainable data mingles in with the explainable parts and skews the models ability to predict as well.
I analyzed some percentiles to decide on a point that I considered to encompass as many outages as possible while I still believed that the duration was going to be mostly explainable. This was somewhere around the 320 minute mark and contained about 90% of the outages.
This was completely subjective to my opinion though and I know there has to be some kind of procedure in order to determine a 'best' cut-off point for this target variable. Ideally, I would like this procedure to be robust enough to consider the trade-off of encompassing as much data as possible and not telling me to make my cut-off 2 hours and thus cutting out a significant amount of customers as the purpose of this is to provide an accurate Estimated Restoration Time to as many customers as possible.
FYI: The methods of modeling I am using that appear to be working the best right now are random forests and conditional random forests. Methods I have used in this scenario include multiple linear regression, decision trees, random forests, and conditional random forests. MLR was by far the least effective. :(
I have exactly the same problem! I hope someone more informed brings his knowledge. I wander to what point is a long duration something that we want to discard or that we want to predict!
Also, I tried treating my data by log transforming it, and the density plot shows a funny artifact on the left side of the distribution ( because I only have durations of integer numbers, not floats). I think this helps, you also should log transform the features that have similar distributions.
I finally thought that the solution should be stratified sampling or giving weights to features, but I don't know exactly how to implement that. My tries didn't produce any good results. Perhaps my data is too stochastic!
How do you evaluate algorithms for calculation of hotness of a post? As in how would you know, which performs better an exponential-decay or the redddit's algo? I understand the question may be a bit naive, but I am looking into performance metrics, or cost functions to help with this?
As with evaluation of any piece of software, you have to first set out problems for it solve and from those derive goals you want to achieve. After you have those, then you can start to determine what metrics will provide a useful approximation of progress towards the goals.
Perhaps you want your site to be great at breaking news. You probably will derive goals from that like "given sufficient votes, a new post should be able to make it to the top 30 listings in the first 10 minutes after it's posted". Then you can build out some test cases and see if you meet them.
Or perhaps you want to be the place with the "best" stuff from across the web. Your goals will weight more heavily towards user approval than newness.
You have to evaluate your own situation to come up with reasonable performance metrics.
I am an undergraduate student and for my graduation thesis I am using SVM to predict the arrival time of a bus to a bus stop in its route. After doing a lot of research and reading some papers I still have a key doubt about how to model my system.
We've decided which features to use and we are in the process of gathering the data required to perform the regression, but what is confusing us are the implications or consequences of using some features as input for the SVM or building separated machines based on some of these features.
For instance, in this paper the authors built 4 SVMs for predicting bus arrival times: one for rush hour on sunny days, rush hour on rainy days, off-rush hour on sunny days and the last one for off-rush hours and rainy days.
But on a following paper on the same subejct they decided to use a single SVM with the weather condition and the rush/off-rush hour as input instead of breaking it in 4 SVMs as before.
I feel like this is the kind of thing that is more about experience so I would like to hear from you guys if anyone has any information about when to choose one of these approaches.
Thanks in advance.
There is no other way: you have to find out on your own. This is why you have to write this thesis. Nobody starts with a perfect solution. Everyone makes mistakes. Your problem is not easy and you cannot say what will work when you have never done anything similar. Try everything you found in the literature, compare the results, develop your own ideas, ...
Most important question: what is the data like?
Second question: what model do you expect to capture this?
So if you want to use SVMs for some reason, keep in mind their basic mechanism is linear, and can only capture non-linear phenomena if data is transformed by a suitable kernel.
For a particular problem at hand that means:
Do you have reason (plots, insights in the problem nature) to believe your problem is linear(ly separable)? Just use one linear svm.
Do you have reason your problem consist of several linear subproblems? Use a linear svm on each of the subproblems.
Does your data seem non-linearly grouped? Try an svm with something like rbf kernel.
Of course, you can just plug in and try, but checking the above may increase understanding of the problem.
In your particular problem I would go for single SVM.
With my not so extensive experience, I would consider breaking a problem in several SVMs for following reasons:
1)The classes are too different, or there are classes and subclasses in your problem.
E.g. in my case: there are several types of antibodies in a microscope image and they all may be positive or negative. So instead of defining A_Pos, A_Neg, B_Pos, B_Neg, ... I decide first if the image is positive or negative and determine the type in second SVM.
2)The feature extraction is too expensive. Provided you have groups of classes, which may be identified with fever features. Instead of extracting all features for a single machine, you may first extract only a small subset, and if required (result not with high enough probability) extract further features.
3)Decide whether the instance belongs to problem at all. Make a model containing one class and all instances of training set. If the instance to be classified is an outlier, stop. Otherwise classify with 2nd SVM containing all classes.
The key-word is "cascaded SVM"