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• Mutual Information / Entropy Calculation Help

  - by Fillip

  Hi, Hoping someone can give me some pointers with this entropy problem. Say X is chosen randomly from the uniform integer distribution 0-32 (inclusive). I calculate the entropy, H(X) = 32 bits, as each Xi has equal probability of occurring. Now, say the following pseudocode executes. int r = rand(0,1); // a random integer 0 or 1 r = r * 33 + X; How would I work out the mutual information between the two variables r and X? Mutual Information is defined as I(X; Y) = H(X) - H(X|Y) but I don't really understand how to apply the conditional entropy H(X|Y) to this problem. Thanks

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• Why is window not identical to window.self in Internet Explorer?

  - by Jim Puls

  There's a convoluted backstory involving how I came across this, but why is the self property not exactly equal to the window itself? In Safari and Firefox and friends, the results are as I'd expect: > window == window.self true > window === window.self true The same isn't true in Internet Explorer, though: >> window == window.self true >> window === window.self false Can anybody account for the inconsistency? To exactly what is the self property of the window object pointing? It casts to something with equality, which is even more vexing.

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• Problem with literal arguments in the PATTERN string for a python 2to3 fixer

  - by Zxaos

  Hi folks. I'm writing a fixer for the 2to3 tool in python. In my pattern string, I have a section where I'd like to match an empty string as an argument, or an empty unicode string. The relevant chunk of my pattern looks like: (args='""' | args='u""') My issue is the second option never matches. Even if it's alone, it won't match. However, if I simply say args=any and then output args, I can catch cases where args is exactly equal to the second option. Is there some weird unicode handling thing going on? Why won't the second literal option ever match?

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• How do I do a join in ActiveRecord after records have been returned?

  - by Russ Bradberry

  I am using ActiveRecord in Rails 3 to pull data from two different tables in two different databases. These databases can not join on each other, but I have the need to do a simple join after-the-fact. I would like to preserve the relation so that I can chain it down the line. here is a simplified version of what I am doing browsers = Browser.all # <-- this is fairly small and can reside in memory events = Event.where(:row_date=>Date.today).select(:name, :browser_id) So as you can see, I want to join browsers in on the events relation, where browser_id should equal browsers.name. events is a relation and I can still add clauses to it down the line, so I dont want to run the query on the db just yet. How would I accomplish this?

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• dragging components in flex

  - by SuperString

  so I am trying to drag around some images in a canvas. I am adding eventlisteners to the components and calling startDrag() and stopDrag() to pick them up and stuff: component.addEventListener(MouseEvent.MOUSE_DOWN, component.startDrag) The problem is that it is selecting the image at its (0,0) location and not where I initially click on it. So there's a sudden "jump" when I click on the image. It is not smooth. I noticed that startDrag() has two default parameters, one of them is lockCenter and it is default to false. Maybe do I set it equal to true somehow? (I don't know how to pass arguments to my second parameter in addeventlistener) Another question: if I want to add more conditions to it, like make a new function that uses component.startDrag(), how do I pass the component to this function while adding event listener to it at the same time? for example: I want to do: component.addEventListener(MouseEvent.MOUSE_DOWN, some_other_function); where some_other_function uses component.startDrag(); Thanks!

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• Remove from a std::set<shared_ptr<T>> by T*

  - by Autopulated

  I have a set of shared pointers: std::set<boost::shared_ptr<T>> set; And a pointer: T* p; I would like to efficiently remove the element of set equal to p, but I can't do this with any of the members of set, or any of the standard algorithms, since T* is a completely different type to boost::shared_ptr<T>. A few approaches I can think of are: somehow constructing a new shared_ptr from the pointer that won't take ownership of the pointed to memory (ideal solution, but I can't see how to do this) wrapping / re-implementing shared_ptr so that I can do the above just doing my own binary search over the set Help!

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• Using unless in rails uniqueness validation

  - by dunxd

  I am just starting out in Rails, and trying to develop a simple application. I need to validate three values submitted to the application - each must meet the same validation criteria. The validation is pretty simple: Value is valid if unqiue, null or equal to "p" or "d". The following gets me halfway there: validates_uniqueness_of :value1, :value2, :value3, :allow_nil => true I think I can use :unless to check whether the value is either "p" or "d", however I can't figure out how. I guess I am trying to combine validates_uniqueness_of with validates_inclusion_of. Any suggestions?

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• What's the best way to return a random line in a text file using C?

  - by jeremy Ruten

  What's the best way to return a random line in a text file using C? It has to use the standard I/O library (<stdio.h>) because it's for Nintendo DS homebrew. Clarifications: Using a header in the file to store the number of lines won't work for what I want to do. I want it to be as random as possible (the best being if each line has an equal probability of being chosen as every other line.) The file will never change while the program is being run. (It's the DS, so no multi-tasking.)

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• Delete element from array

  - by Julio Diaz

  Is there a way I can get rid of some elements in an array. for instance, if i have this array int testArray[] = {0,2,0,3,0,4,5,6} Is there a "fast" way to get rid of the elements that equal 0 int resultArray[] = {2,3,4,5,6} I tried this function but I got lost using Lists public int[] getRidOfZero(int []s){ List<> result=new ArrayList<>(); for(int i=0; i<s.length; i++){ if(s[i]<0){ int temp = s[i]; result.add(temp); } } return result.toArray(new int[]); }

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• Setting package-wide variables during python setup.py install

  - by Morgoth

  Is there a way that when a user types python setup.py install to install a Python package, setup.py can be made to set specific variables at the base of the pacakge? A common example would be to basically set mypackage.__revision__ to be the svn revision of the checkout if one is working from svn. Another example case would be if the user can choose a global option, so that the option mypackage.__option__ be set according to a flag passed to setup.py, e.g. python setup.py install --set-flag=10 Then when using the package, mypackage.__option__ would equal 10.

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• Is there a concise way to create an InputSupplier for an InputStream in Google Guava?

  - by Fabian Steeg

  There are a few factory methods in Google Guava to create InputSuppliers, e.g. from a byte[]: ByteStreams.newInputStreamSupplier(bytes); Or from a File: Files.newInputStreamSupplier(file); Is there a similar way to to create an InputSupplier for a given InputStream? That is, a way that's more concise than an anonymous class: new InputSupplier<InputStream>() { public InputStream getInput() throws IOException { return inputStream; } }; Background: I'd like to use InputStreams with e.g. Files.copy(...) or ByteStreams.equal(...).

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• Problem with updating multiple rows which are in conflict with unique index

  - by GUZ

  I am using Microsoft SQL Server and I have a master-detail scenario where I need to store the order of details. So in the Detail table I have ID, MasterID, Position and some other columns. There is also a unique index on MasterID and Position. It works OK except one case: when I have some existing details and I change their order. For example when I change a detail on position 3 with a detail on position 2. When I save the detail on position 2 (which in the database has Position equal to 3) SQL Server protests, because the index uniqueness constraint. How to solve this problem in a reasonable way? Thank you in advance Lukasz Glaz

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• How to change rows in a table based on other table rows in mysql?

  - by understack

  I've a table which has 3 columns: id, a_id and b_id. Suppose rows are like this: 1, a1, b1 2, a1, b2 3, a1, b3 4, a2, b4 5, a2, b5 6, a2, b6 I want to convert it to 1, a1, b1 2, a1, b1 3, a1, b1 4, a2, b4 5, a2, b4 6, a2, b4 So I want to make all the b_id corresponding to a_id same, and equal to the one which is found first. How can I do this? For simplicity, I've removed other columns from table. So please ignore row duplication here.

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• Distance between numpy arrays, columnwise

  - by Jaapsneep

  I have 2 arrays in 2D, where the column vectors are feature vectors. One array is of size F x A, the other of F x B, where A << B. As an example, for A = 2 and F = 3 (B can be anything): arr1 = np.array( [[1, 4], [2, 5], [3, 6]] ) arr2 = np.array( [[1, 4, 7, 10, ..], [2, 5, 8, 11, ..], [3, 6, 9, 12, ..]] ) I want to calculate the distance between arr1 and a fragment of arr2 that is of equal size (in this case, 3x2), for each possible fragment of arr2. The column vectors are independent of each other, so I believe I should calculate the distance between each column vector in arr1 and a collection of column vectors ranging from i to i + A from arr2 and take the sum of these distances (not sure though). Does numpy offer an efficient way of doing this, or will I have to take slices from the second array and, using another loop, calculate the distance between each column vector in arr1 and the corresponding column vector in the slice?

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• NHibernate - define where condition

  - by t.kehl

  Hi. In my application the user can defines search-conditions. He can choose a column, set an operator (equals, like, greater than, less or equal than, etc.) and give in the value. After the user clicks on a button and the application should do a search on the database with the condition. I use NHibernate and ask me now, what is the efficientest way to do this with NHibernate. Should I create a query with it like (Column=Name, Operator=Like, Value=%John%) var a = session.CreateCriteria<Customer>(); a.Add(Restrictions.Like("Name", "%John%")); return a.List<Customer>(); Or should I do this with HQL: var q = session.CreateQuery("from Customer where " + where); return q.List<Customer >(); Or is there a more bether solution? Thanks for your help. Best Regards, Thomas

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• How to exclude results with get_object_or_404?

  - by googletorp

  In Django you can use the exclude to create SQL similar to not equal. An example could be. Model.objects.exclude(status='deleted') Now this works great and exclude is very flexible. Since I'm a bit lazy, I would like to get that functionality when using get_object_or_404, but I haven't found a way to do this, since you cannot use exclude on get_object_or_404. What I want is to do something like this: model = get_object_or_404(pk=id, status__exclude='deleted') But unfortunately this doesn't work as there isn't an exclude query filter or similar. The best I've come up with so far is doing something like this: object = get_object_or_404(pk=id) if object.status == 'deleted': return HttpResponseNotfound('text') Doing something like that, really defeats the point of using get_object_or_404, since it no longer is a handy one-liner. Alternatively I could do: object = get_object_or_404(pk=id, status__in=['list', 'of', 'items']) But that wouldn't be very maintainable, as I would need to keep the list up to date. I'm wondering if I'm missing some trick or feature in django to use get_object_or_404 to get the desired result?

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• How do I make a sql query where fields are the result of a different query?

  - by CRP

  I have two tables, the first is like this: f1 | f2 | f3 | f4 ----------------- data.... the second contains info about the fields of the first: field | info ------------ f1 a f2 b f3 a etc. I would like to query the first table selecting the fields with a query on the second. So, for example, I might want to get data for fields where info is equal to "a", thus I would do "select f1, f3 from first_table". How do I do this programmatically? I was thinking about something along the lines of select (select fields from second_table where info='a') from first_table Thanks Chris

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• How do I programmatically nullify a File Attachment in InfoPath Forms

  - by Doctor Zinda

  Howdy all, I'm running into a problem with some InfoPath C# code while trying to remove an attachment from a form. Basically the process is: User opens form User clicks button File attachment is cleared I've tried adding a blank attachment to my schema that never becomes populated, then setting the original field's value equal to that value by the method below. When debugging the form I catch an error: Schema validation found non-data type errors. Any tips here would be appreciated. public void BTN_ClearAttachment_Clicked(object sender, ClickedEventArgs e) { try { _OriginalAttachment.SetValue(_BLANK_ATTACHMENT.Value); } catch (Exception ex) { _ErrorField.SetValue(ex.Message + " : " + ex.StackTrace); } } Thanks, Dr Z Edit - P.S. I should clear up that both _OriginalAttachment & _ErrorField are both XPathNavigators, pointing at different schema elements. I've verified that these XPathNavigators are both pointing at valid schema elements.

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• Add the "selected" attribute to a drop down option with jQuery

  - by gaoshan88

  How do I add the attribute "selected" to a drop down menu option based on that option matching some variable? Here is how the dropdown is populated... loginOptions = ["First", "Second", "Third]; var Login = $( '#Login' ); for ( var i = 0; i < loginOptions.length; i++ ) { Login.append('<option value="'+ loginOptions[i] +'">'+ loginOptions[i] +'</option>'); } I want to mark one option as "selected" based on whether or not its value matches another variable. so if loginOption[i] is equal to var existingLoginValue then set that option to 'selected' Something that would do if(loginOptions[i] === existingLoginValue){ print 'selected'; }; Thanks!

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• Container for database-like searches

  - by Milan Babuškov

  I'm looking for some STL, boost, or similar container to use the same way indexes are used in databases to search for record using a query like this: select * from table1 where field1 starting with 'X'; or select * from table1 where field1 like 'X%'; I thought about using std::map, but I cannot because I need to search for fields that "start with" some text, and not those that are "equal to". I could create a sorted vector or list and use binary search (breaking the set in 2 in each step by reading the element in the middle and seeing if it's more or less than 'X'), but I wonder if there is some ready-made container I could use without reinventing the wheel?

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• Why increase pointer by two while finding loop in linked list, why not 3,4,5?

  - by GG

  I had a look at question already which talk about algorithm to find loop in a linked list. I have read Floyd's cycle-finding algorithm solution, mentioned at lot of places that we have to take two pointers. One pointer( slower/tortoise ) is increased by one and other pointer( faster/hare ) is increased by 2. When they are equal we find the loop and if faster pointer reaches null there is no loop in the linked list. Now my question is why we increase faster pointer by 2. Why not something else? Increasing by 2 is necessary or we can increase it by X to get the result. Is it necessary that we will find a loop if we increment faster pointer by 2 or there can be the case where we need to increment by 3 or 5 or x.

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• How to center elements in the BoxLayout using center of the element?

  - by Roman

  I use outputPanel.setLayout(new BoxLayout(outputPanel, BoxLayout.Y_AXIS)); and then I add elements (for example JLabels, JButtons) to the outputPanel. For example: outputPanel.add(submitButton);. I see that all added elements are "centered". It is good, because I do want my elements to be in the center. When I write "center" I mean "equal distance from left and right". But the problem is that the left part of the element is put into the center. And I want to have center of elements to be put into the center. How can I get this behavior?

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 distinct colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 combinations of colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• Construct a variadic template of unsigned int recursively

  - by Vincent

  I need a tricky thing in a C++ 2011 code. Currently, I have a metafunction of this kind : template<unsigned int N, unsigned int M> static constexpr unsigned int myFunction() This function can generate number based on N and M. I would like to write a metafunction with input N and M, and that will recursively construct a variadic template by decrementing M. For example, by calling this function with M = 3, It will construct a variadic template called List equal to : List... = myFunction<N, 3>, myFunction<N, 2>, myFunction<N, 1>, myFunction<N, 0> How to do that (if it is possible of course) ?

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