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• What's an efficient way of calculating the nearest point?

  - by Griffo

  I have objects with location data stored in Core Data, I would like to be able to fetch and display just the nearest point to the current location. I'm aware there are formulas which will calculate the distance from current lat/long to a stored lat/long, but I'm curious about the best way to perform this for a set of 1000+ points stored in Core Data. I know I could just return the points from Core Data to an array and then loop through that looking for the min value for distance between the points but I'd imagine there's a more efficient method, possibly leveraging Core Data in some way. Any insight would be appreciated. EDIT: I don't know how I missed this on my initial search but this SO question suggests just iterating through an array of Core Data objects but limiting the array size with a bounding box based on the current location. Is this the best I can do?

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• Most efficient way to check if a date falls between two dates?

  - by Dave Jarvis

  Given: Start Month & Start Day End Month & End Day Any Year What SQL statement results in TRUE if a date lands between the Start and End days? 1st example: Start Date = 11-22 End Date = 01-17 Year = 2009 Specific Date = 2010-01-14 TRUE 2nd example: Start Date = 11-22 End Date = 11-16 Year = 2009 Specific Date = 2010-11-20 FALSE 3rd example: Start Date = 02-25 End Date = 03-19 Year = 2004 Specific Date = 2004-02-29 TRUE I was thinking of using the MySQL functions datediff and sign plus a CASE condition to determine whether the year wraps, but it seems rather expensive. Am looking for a simple, efficient calculation. Update The problem is the end date cannot simply use the year. The year must be increased if the end month/day combination happens before the start date. The start date is easy: Start Date = date( concat_ws( '-', year, Start Month, Start Day ) The end date is not so simple. Thank you!

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• Is it more efficient to always run a delete query, or to check if that information exists first

  - by Scarface

  Ok this is going to seem like a dumb question to experienced developers, but questions like this bother me until I ask them. So... is it more efficient to always run a delete query by default whether an entry exists or not, for example to delete a user name after a certain period of time (DELETE * from table where username=user), or should you check if that entry exists first using a select query and mysql_num_rows. What uses more processor on the server side? Obviously one approach contains more code, but I was wondering if certain mysql operations used a lot more cpu than others.

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• Most efficient way to solve system of equations involving the digamma function?

  - by Neil G

  What is the most efficient way to solve system of equations involving the digamma function? I have a vector v and I want to solve for a vector w such that for all i: digamma(sum(w)) - digamma(w_i) = v_i and w_i 0 I found the gsl function gsl_sf_psi, which is the digamma function. Is there an identity I can use to reduce the equations? Is my best bet to use a solver? I am using C++0x; which solver is easiest to use and fast?

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• Is there a more efficient way to set variables on a RadioButton's CheckChanged event?

  - by C Patton

  I have 16 radio buttons in an application of mine.. I have to set a variable based on which one was selected.. and I've produced some very ugly code doing this.. private void Foo_CheckedChanged(object sender, EventArgs e) { convertSource = 1; } private void Bar_CheckedChanged(object sender, EventArgs e) { convertSource = 2; } private void Baz_RadioButton_CheckedChanged(object sender, EventArgs e) { convertSource = 3; } Now, I've been thinking about it and to be honest I thought there might have been a way to do it with a switch.. I just can't conceptualize it in my mind. If anyone could show me a more efficient way of doing this, I'd really appreciate it. It's just really bugging me that such a simple thing as this is taking up fifty to seventy lines of code. thanks, cpatton

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• What is the most efficient way to solve system of equations containing the digamma function?

  - by Neil G

  What is the most efficient way to solve system of equations involving the digamma function? I have a vector v and I want to solve for a vector w such that for all i: digamma(sum(w)) - digamma(w_i) = v_i and w_i 0 I found the gsl function gsl_sf_psi, which is the digamma function (calculated using some kind of series.) Is there an identity I can use to reduce the equations? Is my best bet to use a solver? I am using C++0x; which solver is easiest to use and fast?

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• Most Efficient Way of calling an external webservice in Java?

  - by Sudheer

  In one of our applications we need to call the Yahoo Soap Webservice to Get Weather and other related info. I used the wsdl2java tool from axis1.4 and generated th required stubs and wrote a client. I use jsp's use bean to include the client bean and call methods defined in the client which call the yahoo webservice inturn. Now the problem: When users make calls to the jsp the response time of the webservice differs greatly, like for one user it took less then 10 seconds and the other in the same network took more than a minute. I was just wondering if Axis1.4 queues the requests even though the jsps are multithreaded. And finally is there an efficient way of calling the webservice(Yahoo weather). Typically i get around 200 simultaneous requests from my users.

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• Is there a efficient way to do multiple test cases in c?

  - by Ahmed Abdelaal

  I use MS Visual Studio and I am new to C++, so I am just wondering if there is an faster more efficient way to do multiple test cases instead of keep clicking CTRL+F5 and re-opening the console many times. Like for example if I have this code #include <iostream> using namespace std; void main () { int x; cout<<"Enter a number"<<endl; cin>>x; cout<<x*2<<endl; } Is there a way I could try different values of x at once and getting the results together? Thanks

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• Why are difference lists more efficient than regular concatenation?

  - by Craig Innes

  I am currently working my way through the Learn you a haskell book online, and have come to a chapter where the author is explaining that some list concatenations can be ineffiecient: For example ((((a ++ b) ++ c) ++ d) ++ e) ++ f Is supposedly inefficient. The solution the author comes up with is to use 'difference lists' defined as newtype DiffList a = DiffList {getDiffList :: [a] -> [a] } instance Monoid (DiffList a) where mempty = DiffList (\xs -> [] ++ xs) (DiffList f) `mappend` (DiffList g) = DiffList (\xs -> f (g xs)) I am struggling to understand why DiffList is more computationally efficient than a simple concatenation in some cases. Could someone explain to me in simple terms why the above example is so inefficient, and in what way the DiffList solves this problem?

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• Efficient multiple services exposed over c# .NET remoting using more channels or end points?

  - by wb

  I am using remoting over TCP for a prototype distributed server application where I want to have varying multiple services exposed from each remoting server process. In some cases I want the services running from the same process but I don't want whatever is using the service to care about that. I am wondering is it more efficient to have multiple services in the same process going over the same remoting channel distinguished by endpoint URI/URL or should I be creating new channels on different ports for each service in the same process? Using up ports isn't so much of a problem as the number of services will be low and the network and machine configuration is completely controlled. Also its not clear to me if remoting sends the URI string for every single message or just at connection time, and whether if the remoting framework is intelligent enough to reduce work if calls are made on the same machine and even the same process? Thanks in advance.

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• Is converting this ArrayList to a Generic List efficient?

  - by Greg

  The code I'm writing receives an ArrayList from unmanaged code, and this ArrayList will always contain one or more objects of type Grid_Heading_Blk. I've considered changing this ArrayList to a generic List, but I'm unsure if the conversion operation will be so expensive as to nullify the benefits of working with the generic list. Currently, I'm just running a foreach (Grid_Heading_Blk in myArrayList) operation to work with the ArrayList contents after passing the ArrayList to the class that will use it. Should I convert the ArrayList to a generic typed list? And if so, what is the most efficient way of doing so?

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• Most efficient way to fetch and output Content with 2-Level Comments?

  - by awegawef

  I have some content with up to 2-levels of replies. I am wondering what the most efficient way to fetch and output the replies. I should note that I am planning on storing the comments with fields content_id and reply_to, where reply_to refers to which comment it is in reply to (if any). Any criticism on this design is welcome. In pseudo-code (ish), my first attempt would be: # in outputting content CONTENT_ID all_comments = fetch all comments where content_id == CONTENT_ID root_comments = filter all_comments with reply_to == None children_comments = filter all_comments with reply_to != None output_comments = list() for each root_comment children = filter children_comments, reply_to == root_comment.id output_coments.append( (root_comment, children) ) send output_comments to template Is this the best way to do this? Thanks in advance. Edit: On second thought, I'll want to preserve date-order on the comments, so I'll have to do this a bit differently, or at least just sort the comments afterward.

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• What is the most efficient way to list all of the files in a directory (including sub-directories)?

  - by prometheus

  I am writing a servlet which will examine a directory on the server (external to the web container), and recursively search for certain files (by certain files, I mean files that are of a certain extension as well as a certain naming convention). Once these files are found, the servlet responds with a long list of all of the found files (including the full path to the files). My problem is that there are so many files and directories that my servlet goes extremely slow. I was wondering if there was a best practice or existing servlet for this type of problem? Would it be more efficient to simply compile the entire list of files and do the filtering via js/jquery on the client side?

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• What strategies are efficient to handle concurrent reads on heterogeneous multi-core architectures?

  - by fabrizioM

  I am tackling the challenge of using both the capabilities of a 8 core machine and a high-end GPU (Tesla 10). I have one big input file, one thread for each core, and one for the the GPU handling. The Gpu thread, to be efficient, needs a big number of lines from the input, while the Cpu thread needs only one line to proceed (storing multiple lines in a temp buffer was slower). The file doesn't need to be read sequentially. I am using boost. My strategy is to have a mutex on the input stream and each thread locks - unlocks it. This is not optimal because the gpu thread should have a higher precedence when locking the mutex, being the fastest and the most demanding one. I can come up with different solutions but before rush into implementation I would like to have some guidelines. What approach do you use / recommend ?

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• Send data to webserver from C#, what's the most efficient way?

  - by Brian

  I am sending gps coordinates from a windows mobile phone to a webserver using a basic program I wrote in C#. The problem is the data plan on the phone only allows 4 MB per month. I was planning on updating the location every 10 seconds. Currently I am just creating a webrequest every 10 seconds to a php page on the server and the coordinates are passed over in the url, the php page saves them to the database. This generates about 1K of data per request, at this rate I will hit my data limit in less than a day. Is there a more efficient way to do this?

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• Python - Is there a better/efficient way to find a node in tree?

  - by Sej P

  I have a node data structure defined as below and was not sure the find_matching_node method is pythonic or efficient. I am not well versed with generators but think there might be better solution using them. Any ideas? class HierarchyNode(): def __init__(self, nodeId): self.nodeId = nodeId self.children = {} # opted for dictionary to help reduce lookup time def addOrGetChild(self, childNode): return self.children.setdefault(childNode.nodeId,childNode) def find_matching_node(self, node): ''' look for the node in the immediate children of the current node. if not found recursively look for it in the children nodes until gone through all nodes ''' matching_node = self.children.get(node.nodeId) if matching_node: return matching_node else: for child in self.children.itervalues(): matching_node = child.find_matching_node(node) if matching_node: return matching_node return None

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• How to code an efficient blacklist filter function in php?

  - by achairapart

  So, I have three arrays like this: [items] => Array ( [0] => Array ( [id] => someid [title] => sometitle [author] => someauthor ... ) ... ) and also a string with comma separated words to blacklist: $blacklist = "some,words,to,blacklist"; Now I need to match these words with (as they can be one of) id, title, author and show results accordingly. I was thinking of a function like this: $pattern = '('.strtr($blacklist, ",", "|").')'; // should return (some|words|etc) foreach ($items as $item) { if ( !preg_match($pattern,$item['id']) || !preg_match($pattern,$item['title']) || !preg_match($pattern,$item['author']) ) { // show item } } and I wonder if this is the most efficient way to filter the arrays or I should use something with strpos() or filter_var with FILTER_VALIDATE_REGEXP ... Note that this function is repeated per 3 arrays. However, each array will not contain more than 50 items.

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• .NET: efficient way to produce a string from a Dictionary<K,V> ?

  - by Cheeso

  Suppose I have a Dictionary<String,String>, and I want to produce a string representation of it. The "stone tools" way of doing it would be: private static string DictionaryToString(Dictionary<String,String> hash) { var list = new List<String> (); foreach (var kvp in hash) { list.Add(kvp.Key + ":" + kvp.Value); } var result = String.Join(", ", list.ToArray()); return result; } Is there an efficient way to do this in C# using existing extension methods? I know about the ConvertAll() and ForEach() methods on List, that can be used to eliminate foreach loops. Is there a similar method I can use on Dictionary to iterate through the items and accomplish what I want?

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• What is the most efficient functional version of the following imperative code?

  - by justin.r.s.

  I'm learning Scala and I want to know the best way of expressing this imperative pattern using Scala's functional programming capabilities. def f(l: List[Int]): Boolean = { for (e <- l) { if (test(e)) return true } } return false } The best I can come up with is along the lines of: l map { e => test(e) } contains true But this is less efficient since it calls test() on each element, whereas the imperative version stops on the first element that satisfies test(). Is there a more idiomatic functional programming technique I can use to the same effect? The imperative version seems awkward in Scala.

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• Which method of adding items to the ASP.NET Dictionary class is more efficient?

  - by ahmd0

  I'm converting a comma separated list of strings into a dictionary using C# in ASP.NET (by omitting any duplicates): string str = "1,2, 4, 2, 4, item 3,item2, item 3"; //Just a random string for the sake of this example and I was wondering which method is more efficient? 1 - Using try/catch block: Dictionary<string, string> dic = new Dictionary<string, string>(); string[] strs = str.Split(','); foreach (string s in strs) { if (!string.IsNullOrWhiteSpace(s)) { try { string s2 = s.Trim(); dic.Add(s2, s2); } catch { } } } 2 - Or using ContainsKey() method: string[] strs = str.Split(','); foreach (string s in strs) { if (!string.IsNullOrWhiteSpace(s)) { string s2 = s.Trim(); if (!dic.ContainsKey(s2)) dic.Add(s2, s2); } }

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• Efficient determination of which strings in an array are substrings of the others?

  - by byte

  In C#, Say you have an array of strings, which contain only characters '0' and '1': string[] input = { "0101", "101", "11", "010101011" }; And you'd like to build a function: public void IdentifySubstrings(string[] input) { ... } That will produce the following: "0101 is a substring of 010101011" "101 is a substring of 0101" "101 is a substring of 010101011" "11 is a substring of 010101011" And you are NOT able to use built-in string functionality (such as String.Substring). How would one efficiently solve this problem? Of course you could plow through it via brute force, but it just feels like there ought to be a way to accomplish it with a tree (since the only values are 0's and 1's, it feels like a binary tree ought to fit somehow). I've read a little bit about things like suffix trees, but I'm uncertain if that's the right path to be going down. Any efficient solutions you can think of?

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• Most efficient way to maintain a 'set' in SQL Server?

  - by SEVEN YEAR LIBERAL ARTS DEGREE

  I have ~2 million rows or so of data, each row with an artificial PK, and two Id fields (so: PK, ID1, ID2). I have a unique constraint (and index) on ID1+ID2. I get two sorts of updates, both with a distinct ID1 per update. 100-1000 rows of all-new data (ID1 is new) 100-1000 rows of largely, but not necessarily completely overlapping data (ID1 already exists, maybe new ID1+ID2 pairs) What's the most efficient way to maintain this 'set'? Here are the options as I see them: Delete all the rows with ID1, insert all the new rows (yikes) Query all the existing rows from the set of new data ID1+ID2, only insert the new rows Insert all the new rows, ignore inserts that trigger unique constraint violations Any thoughts?

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• In the context of an asp.net website, what's the most efficient way to check whether a User has acce

  - by scaramouch

  I have a webpage that you pass in an id parameter (via a querystring), which it then uses to fetch data from a database. Typically, a user would navigate to this page from another page that lists only those records that the user has access to. However, if they go directly to the page by typing in the URL in the Address Bar, they can effectively view any record they like. Eg. If they were to type something like http://localhost/TestSite/ClientAdmin/ManageLocation.aspx?LocationID=5 into their Address Bar, they can access the database record with the LocationID equal to five - even though they shouldn't have access to it. Now, I could solve this by doing a database check every time the page is loaded to see whether the current user has access to the record they're trying to view. However this doesn't seem very efficient given that in most cases a user won't be trying to access a record that isn't theirs. Does anyone have a better suggestion? Thanks.

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• What is the most efficient way to pass data (list of pairs of [Integer + Double]) between two Google App Engine instances?

  - by ruslan

  What is the most efficient way to pass data (list of pairs of [Integer, Double]) between two Google App Engine instances ? Currently I use Java binary serialization. Frontend servlet receives data from the client in JSON format. I convert it to byte[] using ObjectOutput.writeObject and then send it to backend servlet via HTTP POST. It's not in production yet. Should I just pass client's JSON as it is to backend? It seems more logical. But it's bigger in size. Or should I use Google Protocol Buffers as stated in this benchmark article ? Thank you!!!

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• What's the most efficient way to repeatedly remove leading text using Vim?

  - by John Topley

  What's the most efficient way to remove the text 2010-04-07 14:25:50,773 DEBUG This is a debug log statement - from a log file like the extract below using Vim? 2010-04-07 14:25:50,772 DEBUG This is a debug log statement - 9,8 2010-04-07 14:25:50,772 DEBUG This is a debug log statement - 1,11 2010-04-07 14:25:50,772 DEBUG This is a debug log statement - 5,2 2010-04-07 14:25:50,772 DEBUG This is a debug log statement - 8,4 This is what the result should look like: 9,8 1,11 5,2 8,4 Note that on this occasion I'm using gVim on Windows, so please don't suggest any UNIX programs which may be better suited to the task—I have to do it using Vim.

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