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• removing duplicate strings from a massive array in java efficiently?

  - by Preator Darmatheon

  I'm considering the best possible way to remove duplicates from an (Unsorted) array of strings - the array contains millions or tens of millions of stringz..The array is already prepopulated so the optimization goal is only on removing dups and not preventing dups from initially populating!! I was thinking along the lines of doing a sort and then binary search to get a log(n) search instead of n (linear) search. This would give me nlogn + n searches which althout is better than an unsorted (n^2) search = but this still seems slow. (Was also considering along the lines of hashing but not sure about the throughput) Please help! Looking for an efficient solution that addresses both speed and memory since there are millions of strings involved without using Collections API!

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• Spatial Index for Rectangles With Fast Insert

  - by TheCloudlessSky

  Hello, I'm looking for a data structure that provides indexing for Rectangles. I need the insert algorithm to be as fast as possible since the rectangles will be moving around the screen (think of dragging a rectangle with your mouse to a new position). I've looked into R-Trees, R+Trees, kD-Trees, Quad-Trees and B-Trees but from my understanding insert's are usually slow. I'd prefer to have inserts at sub-linear time complexity so maybe someone can prove me wrong about either of the listed data structures. I should be able to query the data structure for what rectangles are at point(x, y) or what rectangles intersect rectangle(x, y, width, height). EDIT: The reason I want insert so fast is because if you think of a rectangle being moved around the screen, they're going to have to be removed and then re-inserted. Thanks!

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• Will more CPUs/cores help with VS.NET build times?

  - by LoveMeSomeCode

  I was wondering if anyone knew whether Visual Studio .NET had a parallel build process or not? I have a solution with lots of projects, every project has lots of markup/code, lots of types, etc. Just sitting there with intellisense on runs it up to about 700MB. But the build times are really slow and only seem to max out one of my two cpu cores. Does this mean the build process is single threaded? My solution's build dependency chain isn't linear, so I don't see why it couldn't be building some of the projects in parallel. I remember Joel Spolsky blogging about his new SSD, and how it didn't help with compile times, but he didn't mention which compiler he was using. We're using VS 2005. Anyone know how it's compilation works? And is it any different/better in 2008/2010?

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• Implement functionality in PHP?

  - by Rachel

  How can we Implement Bisect Python functionality in PHP Implement function bisect_left($arr, $item); as a pure-PHP routine to do a binary-bisection search for the position at which to insert $item into $list, maintaining the sort order therein. Assumptions: Assume that $arr is already sorted by whatever comparisons would be yielded by the stock PHP < operator, and that it's indexed on ints. The function should return an int, representing the index within the array at which $item would be inserted to maintain the order of the array. The returned index should be below any elements in $arr equal to $item, i.e., the insertion index should be "to the left" of anything equal to $item. Search routine should not be linear! That is, it should honor the name, and should attempt to find it by iteratively bisecting the list and comparing only around the midpoint.

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• How do I write a constant-space length function in Haskell?

  - by Bill

  The canonical implementation of length :: [a] -> Int is: length [] = 0 length (x:xs) = 1 + length xs which is very beautiful but suffers from stack overflow as it uses linear space. The tail-recursive version: length xs = length' xs 0 where length' [] n = n length' (x:xs) n = length xs (n + 1) doesn't suffer from this problem, but I don't understand how this can run in constant space in a lazy language. Isn't the runtime accumulating numerous (n + 1) thunks as it moves through the list? Shouldn't this function Haskell to consume O(n) space and lead to stack overflow? (if it matters, I'm using GHC)

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• Efficient mass string search problem.

  - by Monomer

  The Problem: A large static list of strings is provided. A pattern string comprised of data and wildcard elements (* and ?). The idea is to return all the strings that match the pattern - simple enough. Current Solution: I'm currently using a linear approach of scanning the large list and globbing each entry against the pattern. My Question: Are there any suitable data structures that I can store the large list into such that the search's complexity is less than O(n)? Perhaps something akin to a suffix-trie? I've also considered using bi- and tri-grams in a hashtable, but the logic required in evaluating a match based on a merge of the list of words returned and the pattern is a nightmare, and I'm not convinced its the correct approach.

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• Mercurial - revert back to old version and continue from there

  - by Paolo

  I'm using mercurial locally for a project (it's the only repo there's no pushing/pulling to/from anywhere else). To date it's got a linear history. However, the current thing I'm working on I've now realised is a terrible approach and I want to go back to the version before I started it and implement it a different way. I'm a bit confused with the branch / revert / update -C commands in Mercurial. Basically I want to revert to version 38 (currently on 45) and have my next commits have 38 as a parent and carry on from there. I don't care if revisions 39-45 are lost for ever or end up in a dead-end branch of their own. Which command / set of commands do I need?

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• Matlab postpones disp calls when doing demanding calculations why is that?

  - by Reed Richards

  I am implementing an algorithm in Matlab. Among other things it calculates shortest paths etc. so its quite demanding for my old computer. I've put out disp calls through out the program to see what's happening all the time. However when starting on a particulary heavy for loop the disp seemes not to be called until the loop is over even though it comes before the loop. Why is that? I though that Matlab was really linear or am I just choking it with to many calculations and the disp calls get the lowest priority?

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• Solving the water jug problem

  - by Amit

  While reading through some lecture notes on preliminary number theory, I came across the solution to water jug problem (with two jugs) which is summed as thus: Using the property of the G.C.D of two numbers that GCD(a,b) is the smallest possible linear combination of a and b, and hence a certain quantity Q is only measurable by the 2 jugs, iff Q is a n*GCD(a,b), since Q=sA + tB, where: n = a positive integer A = capacity of jug A B= capacity of jug B And, then the method to the solution is discussed Another model of the solution is to model the various states as a state-space search problem as often resorted to in Artificial Intelligence. My question is: What other known methods exist which models the solution, and how? Google didn't throw up much.

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• Any implementations of graph st-ordering or ear-decomposition?

  - by chang

  I'm in the search for an implementation of an ear-decomposition algorithm (http://www.ics.uci.edu/~eppstein/junkyard/euler/ear.html). I examined networkx and didn't find one. Although the algorithm layout is vaguely in my mind, I'd like to see some reference implementation, too. I'm aware of Ulrik Brandes publication on a linear time Eager st-ordering algorithm, which results in an ear decomposition as a side product, if I understand correctly (it even includes pseudocode, which I'm trying to base my implementation on). Side problem: First step could be an st-ordering of a graph. Are there any implementations for st-ordering algorithms you know? Thanks for your input. I'd really like to contribute e.g. to networkx by implementing the ear-decomposition algorithm in python.

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• Is javac enough to build an OSGi bundle?

  - by Chatanga

  To produce a bundle from source using a tool such as javac, you need to provide it with a linear classpath. Unfortunately, it won't work in some situations still perfectly legal from an OSGi point of view: dependencies with embedded JAR in them; same packages contained by different dependencies. Since javac doesn't understand OSGi metadata, I won't be able to simply but the dependencies in a classpath. A finer package grained approach seems necessary. How this problem is addressed by people using OSGi in an automated process (continuous integration)? Strangely, there is a lot of resources on the web on how to create bundle JAR (creating the metadata, creating the JAR) provided you have the classes/inner JAR to put inside, but very few things on how actually get theses classes compiled.

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• Use XSLT to arrange a list of items in a table

  - by Mark Sp

  I have a linear list of items which I wish to arrange in a table using XSLT. I wish to specify the number of columns as a parameter. For example, if I have a list of 12 items, I can select a 2x6, 3x4, 4x3 or 6x2 table. I cannot see a general way to do this. I have seen this article: http://www.nedcomp.nl/support/origdocs/xml4/extracted/xpath_hdi_1_4llx.aspx It tells you how to generate a table with a specific number of columns, but does not allow a general case. (Ideally there would be a loop for the xsl:value-of lines). Thanks Mark

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• UITableView Cell IndexPath

  - by Reonarudo

  Hello, Can anyone tell me how can I get a cell IndexPath? I was saving the IndexPath in the tableView: cellForRowAtIndexPath: method but this only loads when the cell is viewed and I need to know its index path on the viewDidLoad method. this resulted in a null value because as I said it only loads its value after the cell was viewed once. Thank you. EDIT The intention is being able to jump to a specific cell that has its specific number but its not linear with the sections and rows count.

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• maths: motion depending on time

  - by clamp

  hello, i have a mathematical problem: i have a function where the only parameter is the current time. the return should be a position which is used to place an object on a certain place. int position(int time) { int x = 0; //TODO implement x depending on time return x; } so basically the function is called every frame to put the object in motion. the motion should look like this (this is the actual question): a linear motion for time A, the object moves at constant speed no motion for time B, the object is stopped repeat at 1. thanks!

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• Using Python tuples as vectors

  - by Etaoin

  I need to represent immutable vectors in Python ("vectors" as in linear algebra, not as in programming). The tuple seems like an obvious choice. The trouble is when I need to implement things like addition and scalar multiplication. If a and b are vectors, and c is a number, the best I can think of is this: tuple(map(lambda x,y: x + y, a, b)) # add vectors 'a' and 'b' tuple(map(lambda x: x * c, a)) # multiply vector 'a' by scalar 'c' which seems inelegant; there should be a clearer, simpler way to get this done -- not to mention avoiding the call to tuple, since map returns a list. Is there a better option?

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• 2-way anova on unbalanced dataset

  - by mortalitysequence

  Is aov appropriate for unbalanced datasets. According to help ...provides a wrapper to lm for fitting linear models to balanced or unbalanced experimental designs. But later on it says aov is designed for balanced designs, and the results can be hard to interpret without balance. How should I perform a 2-way anova on an unbalanced dataset in R? I would like to reproduce the different results for type I and type III sum of squares of SAS output (when using proc glm). I remember we were using type III sum of squares for unbalanced datasets. Thank you in advance.

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• Difference between BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION?

  - by Rhys Ulerich

  Can anyone describe the difference in behavior between BOOST_CHECK_CLOSE and BOOST_CHECK_CLOSE_FRACTION? The documentation implies the that both macros treat their third parameter identically, which makes me suspect the documentation is wrong. In particular, BOOST_CHECK_CLOSE_FRACTION gives me some odd looking results: error in "...": difference between *expected{0} and *actual{-1.7763568394002506e-16} exceeds 9.9999999999999995e-07 Is there a gotcha because I expect a zero result? I've not been successful at reading through the underlying macro declarations. Please note BOOST_CHECK_SMALL isn't appropriate for my use case (comparing two vectors after a linear algebra operation).

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• tracing a linux kernel, function-by function (biggest only) with us timer

  - by osgx

  Hello I want to know, how does the linux kernel do some stuff (receiving a tcp packet). In what order main tcp functions are called. I want to see both interrupt handler (top half), bottom half and even work done by kernel after user calls "read()". How can I get a function trace from kernel with some linear time scale? I want to get a trace from single packet, not the profile of kernel when receiving 1000th of packets. Kernel is 2.6.18 or 2.6.23 (supported in my debian). I can add some patches to it.

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• How to make scipy.interpolate give a an extrapolated result beyond the input range?

  - by Salim Fadhley

  I'm trying to port a program which uses a hand-rolled interpolator (developed by a mathematitian colleage) over to use the interpolators provided by scipy. I'd like to use or wrap the scipy interpolator so that it has as close as possible behavior to the old interpolator. A key difference between the two functions is that in our original interpolator - if the input value is above or below the input range, our original interpolator will extrapolate the result. If you try this with the scipy interpolator it raises a ValueError. Consider this program as an example: import numpy as np from scipy import interpolate x = np.arange(0,10) y = np.exp(-x/3.0) f = interpolate.interp1d(x, y) print f(9) print f(11) # Causes ValueError, because it's greater than max(x) Is there a sensible way to make it so that instead of crashing, the final line will simply do a linear extrapolate, continuing the gradients defined by the first and last two pouints to infinity. Note, that in the real software I'm not actually using the exp function - that's here for illustration only!

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• Git: removing selected commits from repository

  - by xk0der

  I would like to remove selected commits from a linear commit tree, so that the commits do not show in the commit log. My commit tree looks something like: R--A--B--C--D--E--HEAD I would like to remove the B and C commits. So that they do not show in the commit log, but changes from A to D should be preserved. Maybe by introducing a single commit, so that B and C become BC and the tree looks like. R--A--BC--D--E--HEAD Or, ideally, after A comes D directly. D' representing changes from A to B, B to C and C to D. R--A--D'--E--HEAD Is this possible? if yes, how? Some notes that might be helpful: This is a fairly new project so has no branches as of now, hence no merges as well. Side note: It's a personal project, so no, I'm not trying to destroy any evidence :)

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• Beginner's resources/introductions to classification algorithms.

  - by Dirk

  Hi, everybody. I am entirely new to the topic of classification algorithms, and need a few good pointers about where to start some "serious reading". I am right now in the process of finding out, whether machine learning and automated classification algorithms could be a worthwhile thing to add to some application of mine. I already scanned through "How to Solve It: Modern heuristics" by Z. Michalewicz and D. Fogel (in particular, the chapters about linear classifiers using neuronal networks), and on the practical side, I am currently looking through the WEKA toolkit source code. My next (planned) step would be to dive into the realm of Bayesian classification algorithms. Unfortunately, I am lacking a serious theoretical foundation in this area (let alone, having used it in any way as of yet), so any hints at where to look next would be appreciated; in particular, a good introduction of available classification algorithms would be helpful. Being more a craftsman and less a theoretician, the more practical, the better... Hints, anyone?

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• How to use custom color for each textview in listview that extends SimpleAdapter in Android ?

  - by mob-king

  I have a listview with custom rows and that extends SimpleAdapter. Each row consist of two linear layouts : 1st having two textviews of which one is hidden in horizontal orientation, second having two textviews in horizontal orientation. Now depending on the value in hidden textview , I want to setcolor for the remaining items for the row. To put it as simple: each listview item has some custom colors the value of which comes from the hidden field. I have done this by overriding getview() for the simpleadapter and returning view for each, but this makes list very slow to render (and that I think is obvious as so much of work for each view before showing it). Can I do this in some more efficient way ? like making views and then add up to list instead of using xml layout maybe one solution OR any other ? Any help ? Thanks.

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• Why my buttons OnClick event fails to fire?

  - by Pentium10

  I have an activity, where the ListView holds customized linear layout elements for each row. One of the rows has a button defined as: <Button android:text="Pick a contact" android:id="@+id/btnPickContact" android:layout_width="wrap_content" android:gravity="center_vertical" android:layout_height="wrap_content"></Button> Then in java, I have this code: ((Button) row.findViewById(R.id.btnPickContact)).setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI); intent.putExtra(EXTRA_ONLINE_ID, (String)v.getTag(TAG_ONLINE_ID)); act.startActivityForResult(intent, PICK_CONTACT); } }); In this setup the event fails to start. Also I've tried by implementing the interface: @Override public void onClick(View v) { Intent intent = new Intent(Intent.ACTION_PICK, ContactsContract.Contacts.CONTENT_URI); intent.putExtra(EXTRA_ONLINE_ID, (String)v.getTag(TAG_ONLINE_ID)); startActivityForResult(intent, PICK_CONTACT); } still no luck, the event doesn't fire. What to do?

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• Python - How to find a correlation between two vectors ?

  - by psihodelia

  Given two vectors X and Y I have to find their correlation, i.e. their linear dependence/independence. Both vectors have equal dimension. A resulted answer should be a floating point number from [-1.0 .. 1.0]. Example: X=[-1, 2, 0] Y=[ 4, 2, -0.3] Find y=cor(X,Y) such that y belongs to [-1.0 .. 1.0]. It should be a simple construction involving a list-comprehension. No external library is allowed. UPDATE: ok, if dot product is enough, then here is my solution: nX = 1/(sum([x*x for x in X]) ** 0.5) nY = 1/(sum([y*y for y in Y]) ** 0.5) cor = sum([(x*nX)*(y*nY) for x,y in zip(X,Y) ]) right?

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• Typecasting a floating value or using the math.h floor* functions?

  - by nobody

  Hi, I am coding up an implementation of Interpolation Search in C. The question is actually rather simple, I need to use the floating operations to do linear interpolation to find the correct index which will eventually be an integer result. In particular my probe index is: t = i + floor((((k-low)/(high-low)) * (j-i))); where, i,j,k,t are unsigned ints, and high,low are doubles. Would this be equivalent to: t = i + (unsigned int)(((k-low)/(high-low)) * (j-i)); Is there any reason I would actually want to use math.h floor* functions over just a simple (int) typecast?

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