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• What are some exciting, fun, and educational Computer Science activities for students?

  - by Nixuz

  I am a volunteer for Let's Talk Science, an organization which places science graduate students into elementary school and high school classrooms to present short, fun, yet educational demonstrations or experiments related to their particular field. Physics, Chemistry, and Biology have an abundance of such demonstrations, however as a computer scientist, I have no good ideas of what I can present to these students which will demonstrate computer programming and computers in an understandable yet inspiring way in only a 1 - 3 hour presentation. So I am turning to SO for suggestions. Thanks. Presentation Requirements Length: 1 - 3 hours. Explainable in a single sitting. Captivates elementary school and high school audiences. Educational. Please Note Computer's are available at the schools. Please, indicate the suitable age range for your suggestion in your answer.

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• How can I draw a log-normalized imshow plot with a colorbar representing the raw data in matplotlib

  - by Adam Fraser

  I'm using matplotlib to plot log-normalized images but I would like the original raw image data to be represented in the colorbar rather than the [0-1] interval. I get the feeling there's a more matplotlib'y way of doing this by using some sort of normalization object and not transforming the data beforehand... in any case, there could be negative values in the raw image. import matplotlib.pyplot as plt import numpy as np def log_transform(im): '''returns log(image) scaled to the interval [0,1]''' try: (min, max) = (im[im > 0].min(), im.max()) if (max > min) and (max > 0): return (np.log(im.clip(min, max)) - np.log(min)) / (np.log(max) - np.log(min)) except: pass return im a = np.ones((100,100)) for i in range(100): a[i] = i f = plt.figure() ax = f.add_subplot(111) res = ax.imshow(log_transform(a)) # the colorbar drawn shows [0-1], but I want to see [0-99] cb = f.colorbar(res) I've tried using cb.set_array, but that didn't appear to do anything, and cb.set_clim, but that rescales the colors completely. Thanks in advance for any help :)

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• Are there cross-platform tools to write XSS attacks directly to the database?

  - by Joachim Sauer

  I've recently found this blog entry on a tool that writes XSS attacks directly to the database. It looks like a terribly good way to scan an application for weaknesses in my applications. I've tried to run it on Mono, since my development platform is Linux. Unfortunately it crashes with a System.ArgumentNullException deep inside Microsoft.Practices.EnterpriseLibrary and I seem to be unable to find sufficient information about the software (it seems to be a single-shot project, with no homepage and no further development). Is anyone aware of a similar tool? Preferably it should be: cross-platform (Java, Python, .NET/Mono, even cross-platform C is ok) open source (I really like being able to audit my security tools) able to talk to a wide range of DB products (the big ones are most important: MySQL, Oracle, SQL Server, ...)

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• How to determine pixel color of System.Windows.Controls.Image?

  - by csciguy

  I have an Image from (System.Windows.Controls.Image). This image is positioned on a main canvas. I want to determine the alpha channel value of the mouse cursor when I click on any portion of this image. When doing something like the following, I'm getting an exception. {"Value does not fall within the expected range."} System.Exception {System.ArgumentException} Code: try{ CroppedBitmap cb = new CroppedBitmap(ac.displayImage.Source as BitmapSource, new Int32Rect((int)mousePoint.X, (int)mousePoint.Y, 1, 1)); byte[] pixels = new byte[4]; cb.CopyPixels(pixels, 4, 0); } catch (Exception ex) { System.Diagnostics.Debug.WriteLine(ex.Message); } The mousePoint.X, and mousePoint.Y are obtained when the user clicks on the main window. Is there a better way to do this?

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• What are Android different screens dimensions in dp for different screens (e.g. xlarge = 960dp x 720dp)?

  - by Zizo

  in this link: Range of screens supported, Android team mentioned that: As you design your UI for different screen sizes, you'll discover that each design requires a minimum amount of space. So, each generalized screen size above has an associated minimum resolution that's defined by the system. These minimum sizes are in "dp" units—the same units you should use when defining your layouts—which allows the system to avoid worrying about changes in screen density. xlarge screens are at least 960dp x 720dp large screens are at least 640dp x 480dp normal screens are at least 470dp x 320dp small screens are at least 426dp x 320dp So, If I want to support all Android screens, can I create images, for full screen view, in those dimensions and that will be sufficient condition to support all available screens? or they are just the minimum sizes, and I need other dimensions? If other dimensions are needed, Please list them as in the list above. Thanks in Advance.

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• Rails advanced queries with join and sum calculation

  - by Dustin Brewer

  I have two models: companies and expenses. Companies have many expenses and expenses belong to companies. My expense model has an 'amount' column. I was wondering if there is a way to perform a find based on a date range and the amount column of the expenses. Something like top 3 companies by total expense amounts over a 7 day period. I've tried for the better part of the day to get this to work, I've attempted joins, chaining named scopes, raw sql, etc. and I'm not having any luck. Thanks for the help.

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• How Do I create a synchronous version of NSURLConnection

  - by quinn

  I am using NSURLConnection inside of an NSIncrementalStore to synchronize my NSManagedObject with rest based web service built in Rails. I am aware of +sendSynchronousRequest:returningResponse:error but my understanding is that will not allow me to access such things as the HTTP response status code which I will need to properly handle the response, my understanding is sendSynchronousRequest returns the data if it responds in the 200 range and fails if it doesn't and doesn't really give you much more than that. I'm assuming I will somehow have to block the current method call after the NSURLConnection is instantiated and unblock it after NSURLConnection's delegate sets some value that can be returned by the blocked method. I'm assuming this will involve some combination of NSLock and NSThread but I really don't know where to start with this, any help will be greatly appreciated, thank you.

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• What regular expression do I need to check for some non-latin characters?

  - by zeckdude

  I am checking a field if it is Latin Characters or not. var foreignCharacters = $("#foreign_characters").val(); var rlatins = /[\u0000-\u007f]/; if (rlatins.test(foreignCharacters)) { alert("This is Latin Characters"); } else { alert("This is non-latin Characters"); } This works well, but I would like to change it so when I enter any non-latin characters, such as chinese characters, along with a space(which is within that range I am using currently) it will still say it is non-latin characters. How can I change the regular expression I have to do that?

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• Should I use implicit conversions to enforce preconditions?

  - by Malvolio

  It occurs to me that I could use use implicit conversions to both announce and enforce preconditions. Consider this: object NonNegativeDouble { implicit def int2nnd(d : Double) : NonNegativeDouble = new NonNegativeDouble(d) implicit def nnd2int(d : NonNegativeDouble) : Double = d.v def sqrt(n : NonNegativeDouble) : NonNegativeDouble = scala.math.sqrt(n) } class NonNegativeDouble(val v : Double ) { if (v < 0) { throw new IllegalArgumentException("negative value") } } object Test { def t1 = { val d : Double = NonNegativeDouble.sqrt(3.0); printf("%f\n", d); val n : Double = NonNegativeDouble.sqrt(-3.0); } } Ignore for the moment the actual vacuity of the example: my point is, the subclass NonNegativeDouble expresses the notion that a function only takes a subset of the entire range of the class's values. First is this: A good idea, a bad idea, or an obvious idea everybody else already knows about Second, this would be most useful with basic types, like Int and String. Those classes are final, of course, so is there a good way to not only use the restricted type in functions (that's what the second implicit is for) but also delegate to all methods on the underlying value (short of hand-implementing every delegation)?

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• Create an automatic date stamp in excel from an entry.

  - by Obfus

  I am trying to have a date stamp event happen in column B when an entry is made in column A. Now i can do this in VBA with no problem, the trouble i am running into is there is also a entry that will eventually go in say column D and would need a date stamp in column E as well. is this possible. here is a sample of the code i have used so far. Private Sub Worksheet_Change(ByVal Target As Range) For Each Cell In Target If Cell.Column <= 3 Then If Cells(Cell.Row, 1) < "" Then Cells(Cell.Row, 2) = Now End If Next Cell End Sub

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• Java string too long?

  - by wrongusername

  I have the following code in Java (which worked just fine in C++ for some reason) which produces an error: int a; System.out.println("String length: " + input.length()); for(a = 0; ((a + 1) * 97) < input.length(); a++) { System.out.print("Substring at " + a + ": "); System.out.println(input.substring(a * 97, 97)); //other code here... } Output: String length: 340 Substring at 0: HelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHe Substring at 1: Exception in thread "AWT-EventQueue-0" java.lang.StringIndexOutOfBoundsException: String index out of range: -97 //long list of "at ..." stuff Substring at 2: Using a string of length 200, however, the following output is produced: String length: 200 Substring at 0: HelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHelloHe Substring at 1: That is it; no exceptions raised, just... nothing. What is happening here?

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• Is there a standard Cyclic Iterator in C++

  - by Hippicoder

  Based on the following question: Check if one string is a rotation of other string I was thinking of making a cyclic iterator type that takes a range, and would be able to solve the above problem like so: std::string s1 = "abc" ; std::string s2 = "bca" ; std::size_t n = 2; // number of cycles cyclic_iterator it(s2.begin(),s2.end(),n); cyclic_iterator end; if (std::search(it, end, s1.begin(),s1.end()) != end) { std::cout << "s1 is a rotation of s2" << std::endl; } My question, Is there already something like this available? I've check Boost and STL doesn't have one. I've got a simple hand-written one but would rather use an already made/tested implementation.

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• MPI4Py Scatter sendbuf Argument Type?

  - by Noel

  I'm having trouble with the Scatter function in the MPI4Py Python module. My assumption is that I should be able to pass it a single list for the sendbuffer. However, I'm getting a consistent error message when I do that, or indeed add the other two arguments, recvbuf and root: File "code/step3.py", line 682, in subbox_grid i = mpi_communicator.Scatter(station_range, station_data) File "Comm.pyx", line 427, in mpi4py.MPI.Comm.Scatter (src/ mpi4py_MPI.c:44993) File "message.pxi", line 321, in mpi4py.MPI._p_msg_cco.for_scatter (src/mpi4py_MPI.c:14497) File "message.pxi", line 232, in mpi4py.MPI._p_msg_cco.for_cco_send (src/mpi4py_MPI.c:13630) File "message.pxi", line 36, in mpi4py.MPI.message_simple (src/ mpi4py_MPI.c:11904) ValueError: message: expecting 2 or 3 items Here is the relevant code snipped, starting a few lines above 682 mentioned above. for station in stations #snip--do some stuff with station station_data = [] station_range = range(1,len(station)) mpi_communicator = MPI.COMM_WORLD i = mpi_communicator.Scatter(station_range, nsm) #snip--do some stuff with station[i] nsm = combine(avg, wt, dnew, nf1, nl1, wti[i], wtm, station[i].id) station_data = mpi_communicator.Gather(station_range, nsm) I've tried a number of combinations initializing station_range, but I must not be understanding the Scatter argument types properly. Does a Python/MPI guru have a clarification this?

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• VBA Add to Array and Use Previous Value

  - by MattHead93

  I'm trying to write some code that will take a value WeekNum, and add it to an array Week(1 To 51), and then associate a value from a Textbox TargDef. Once this has been added to the array, I want to look up the value of the array for the previous WeekNum and add it to a value ProdTarg. I've created this much so far: Dim Week(1 To 51) Dim Count As Integer If TargDef < 0 Then Count = WeekNum Week(Count) = Abs(Val(TargDef)) If Val(Week((Count) - 1)) = 0 Then ProdTarg = Val(ProdTarg) Else ProdTard = Val(ProdTarg) + Val(Week((Count) - 1)) End If End If I am currently receiving the error "Subscript out of Range" for the line If Val(Week((Count) - 1)) = 0 Then Any help will be greatly appreciated!

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• Excel, VBA Vlookup, multiple returns into rows

  - by Sean Mc

  Very new to VBA, so please excuse my ignorance. How would you alter the code below to return the result into rows as opposed to a string? Thanks in advance.... data Acct No CropType ------- --------- 0001 Grain 0001 OilSeed 0001 Hay 0002 Grain function =vlookupall("0001", A:A, 1, " ") Here is the code: Function VLookupAll(ByVal lookup_value As String, _ ByVal lookup_column As range, _ ByVal return_value_column As Long, _ Optional seperator As String = ", ") As String Application.ScreenUpdating = False Dim i As Long Dim result As String For i = 1 To lookup_column.Rows.count If Len(lookup_column(i, 1).text) <> 0 Then If lookup_column(i, 1).text = lookup_value Then result = result & (lookup_column(i).offset(0, return_value_column).text & seperator) End If End If Next If Len(result) <> 0 Then result = Left(result, Len(result) - Len(seperator)) End If VLookupAll = result Application.ScreenUpdating = True End FunctionNotes:

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• Find out 20th, 30th, nth prime number. (I'm getting 20th but not 30th?) [Python]

  - by gsin

  The question is to find the 1000th prime number. I wrote the following python code for this. The problem is, I get the right answer for the 10th , 20th prime but after that each increment of 10 leaves me one off the mark. I can't catch the bug here :( count=1 #to keep count of prime numbers primes=() #tuple to hold primes candidate=3 #variable to test for primes while count<20: for x in range(2,candidate): if candidate%x==0: candidate=candidate+2 else : pass primes=primes+(candidate,) candidate=candidate+2 count=count+1 print primes print "20th prime is ", primes[-1] In case you're wondering, count is initialised as 1 because I am not testing for 2 as a prime number(I'm starting from 3) and candidate is being incremented by 2 because only odd numbers can be prime numbers. I know there are other ways of solving this problem, such as the prime number theorem but I wanna know what's wrong with this approach. Also if there are any optimisations you have in mind, please suggest. Thank You

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• C typedef struct uncertainty.

  - by Emanuel Ey

  Consider the following typedef struct in C: 21:typedef struct source{ 22: double ds; //ray step 23: double rx,zx; //source coords 24: double rbox1, rbox2; //the box that limits the range of the rays 25: double freqx; //source frequency 26: int64_t nThetas; //number of launching angles 27: double theta1, thetaN; //first and last launching angle 28:}source_t; I get the error: globals.h:21: error: redefinition of 'struct source' globals.h:28: error: conflicting types for 'source_t' globals.h:28: note: previous declaration of 'source_t' was here I've tried using other formats for this definition: struct source{ ... }; typedef struct source source_t; and typedef struct{ ... }source_t; Which both return the same error. Why does this happen? it looks perfectly right to me.

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• Storing a bucket of numbers in an efficient data structure

  - by BlitzKrieg

  I have a buckets of numbers e.g. - 1 to 4, 5 to 15, 16 to 21, 22 to 34,.... I have roughly 600,000 such buckets. The range of numbers that fall in each of the bucket varies. I need to store these buckets in a suitable data structure so that the lookups for a number is as fast as possible. So my question is what is the suitable data structure and a sorting mechanism for this type of problem. Thanks in advance

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• Masking to Transparent returns empty image

  - by Tibi

  Hi there, I'm trying to put white color in my images to transparent with the following code. Problem is that "CGImageRef maskedTransparent" is blank. I don't understand because the code I'm using is nearly a copy paste from the doc ... Any idea ? (UIImage*) maskImage:(UIImage *)image withMask:(UIImage *)maskImage { CGImageRef maskRef = maskImage.CGImage; CGImageRef mask = CGImageMaskCreate(CGImageGetWidth(maskRef), CGImageGetHeight(maskRef), CGImageGetBitsPerComponent(maskRef), CGImageGetBitsPerPixel(maskRef), CGImageGetBytesPerRow(maskRef), CGImageGetDataProvider(maskRef), NULL, false); CGImageRef masked = CGImageCreateWithMask([image CGImage], mask); //Array defining min & max RGB values to be transformed to transparent colors. float maskingMinMax[6] = {255, 255, 255, 255, 255, 255}; //masking image to remove range in maskinLinMax CGImageRef maskedTransparent = CGImageCreateWithMaskingColors(masked, maskingMinMax); return [UIImage imageWithCGImage:maskedTransparent]; }

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• What is the advantage of using static methods in Python?

  - by Curious2learn

  I ran into unbound method error in python with the code class Sample(object): '''This class defines various methods related to the sample''' def drawSample(samplesize,List): sample=random.sample(List,samplesize) return sample Choices=range(100) print Sample.drawSample(5,Choices) After reading many helpful posts here, I figured how I could add @staticmethod above to get the code working. I am python newbie. Can someone please explain why one would want to define static methods? Or, why are not all methods defined as static methods. Thanks in advance.

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• Python or matplotlib limitation error

  - by Werner

  Hi, I wrote an algorithm using python and matplotlib that generates histograms from some text input data. When the number of data input is approx. greater than 15000, I get in the (append) line of my code: mydata = [] for i in range(len(data)): mydata.append(string.atof(data[i])) the error: Traceback (most recent call last): File "get_histogram_picture.py", line 25, in <module> mydata.append(string.atof(data[i])) File "/usr/lib/python2.6/string.py", line 388, in atof return _float(s) ValueError: invalid literal for float(): -a can it be an error in python ? What is the solution ? Thanks

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• What's the fastest way to strip and replace a document of high unicode characters using Python?

  - by Rhubarb

  I am looking to replace from a large document all high unicode characters, such as accented Es, left and right quotes, etc., with "normal" counterparts in the low range, such as a regular 'E', and straight quotes. I need to perform this on a very large document rather often. I see an example of this in what I think might be perl here: http://www.designmeme.com/mtplugins/lowdown.txt Is there a fast way of doing this in Python without using s.replace(...).replace(...).replace(...)...? I've tried this on just a few characters to replace and the document stripping became really slow.

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• What's the best example of pure show-off code you've seen?

  - by Damovisa

  Let's face it, programmers can be show-offs. I've seen a lot of code that was only done a particular way to prove how smart the person who wrote it was. What's the best example of pure show-off code you've seen (or been responsible for) in your time? For me, it'd have to be the guy who wrote FizzBuzz in one line on a whiteboard during a programming interview. Not really that impressive in the scheme of things, but completely unnecessary and pure, "look-what-I-can-do". I've lost the original code, but I think it was something like this (linebreaks for readability): Enumerable.Range(1,100).ToList().ForEach( n => Console.WriteLine( (n%3==0) ? (n%5==0) ? "FizzBuzz" : "Fizz" : (n%5==0) ? "Buzz" : n ) );

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• Encoding with url and api

  - by user2950824

  So I have this web app set up and running and it works fine for any username that you request, but when i try http://mrcastelo.pythonanywhere.com/lol/euw/Nazaré, it simply doesnt work - the error that I get on the server is the following: iddata= getJSON(urllolbase+region+urlid+username) #SummonerID UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 5: ordinal not in range(128) It is annoying me greatly, I've tried some other threads but none of them came to a fix. The api that I am using (www.legendaryapi.com) does accept this because this works. Any idea on how to fix this?

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• Convert CString to string (VC6)

  - by Yan Cheng CHEOK

  I want to convert CString to string. (Yup. I know what am I doing. I know the returned string will be incorrect, if CString value range is outside ANSI, but That's Is OK!) The following code will work under VC2008. std::string Utils::CString2String(const CString& cString) { // Convert a TCHAR string to a LPCSTR CT2CA pszConvertedAnsiString (cString); // construct a std::string using the LPCSTR input std::string strStd (pszConvertedAnsiString); return strStd; } But VC6 doesn't have CT2CA macro. How I can make the code to work as well in both VC6 and VC2008?

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