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• Any way to avoid a filesort when order by is different to where clause?

  - by Julian

  I have an incredibly simple query (table type InnoDb) and EXPLAIN says that MySQL must do an extra pass to find out how to retrieve the rows in sorted order. SELECT * FROM `comments` WHERE (commentable_id = 1976) ORDER BY created_at desc LIMIT 0, 5 exact explain output: table select_type type extra possible_keys key key length ref rows comments simple ref using where; using filesort common_lookups common_lookups 5 const 89 commentable_id is indexed. Comments has nothing trick in it, just a content field. The manual suggests that if the order by is different to the where, there is no way filesort can be avoided. http://dev.mysql.com/doc/refman/5.0/en/order-by-optimization.html I also tried order by id as well as it's equivalent but makes no difference, even if I add id as an index (which I understand is not required as id is indexed implicitly in MySQL). thanks in advance for any ideas!

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• Is there a difference between `==` and `is` in python?

  - by Bernard

  My Google-fu has failed me. In Python, are these: n = 5 # Test one. if n == 5: print 'Yay!' # Test two. if n is 5: print 'Yay!' two tests for equality equivalent (ha!)? Does this hold true for objects where you would be comparing instances (a list say)? Okay, so this kind of answers my question: l = list() l.append(1) if l == [1]: print 'Yay!' # Holds true, but... if l is [1]: print 'Yay!' # Doesn't. So == tests value where is tests to see if they are the same object?

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• Constructing a tree using Python

  - by stealthspy

  I am trying to implement a unranked boolean retrieval. For this, I need to construct a tree and perform a DFS to retrieve documents. I have the leaf nodes but I am having difficulty to construct the tree. Eg: query = OR ( AND (maria sharapova) tennis) Result: OR | | AND tennis | | maria sharapova I traverse the tree using DFS and calculate the boolean equivalent of certain document ids to identify the required document from the corpus. Can someone help me with the design of this using python? I have parsed the query and retrieved the leaf nodes for now.

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• Ping or otherwise tell if a device is on the network by MAC in C#

  - by Aric TenEyck

  I'm developing a home security application. One thing I'd like to do is automatically turn it off and on based on whether or not I'm at home. I have a phone with Wifi that automatically connects to my network when I'm home. The phone connects and gets its address via DHCP. While I could configure it to use a static IP, I'd rather not. Is there any kind of 'Ping' or equivalent in C# / .Net that can take the MAC address of a device and tell me whether or not it's currently active on the network?

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• list all functions on CRAN

  - by baptiste

  Suppose I'm trying to run a script of unknown origin, and one of the functions is from a package that is not loaded by the script (an oversight, maybe it was loaded in the .Rprofile of the person who wrote it). How can I find in which package this function resides? There's some information compiled on CRAN, that doesn't require the user to download/install all R packages locally; however as far as I could tell it only gives access to the DESCRIPTION files. RSiteSearch, and its web equivalent, seem to access an online database of all CRAN packages, where presumably a list of all functions would be available. Is there some way of accessing this information? Thanks. Edit: I know sos::findFn, utils::RSiteSearch and search.r-project; what I would like is to get the raw data that these tools use.

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• INSERT 0..n records into table 'A' based on content of table 'B' in MySql 5

  - by Robert Gowland

  Using MySql 5, I have a task where I need to update one table based on the contents of another table. For example, I need to add 'A1' to table 'A' if table 'B' contains 'B1'. I need to add 'A2a' and 'A2b' to table 'A' if table 'B' contains 'B2', etc.. In our case, the value in table 'B' we're interested is an enum. Right now I have a stored procedure containing a series of statements like: INSERT INTO A SELECT 'A1' FROM B WHERE B.Value = 'B1'; --Repeat for 'B2' -> 'A2a'; 'B2' -> 'A2b'; 'B3' -> 'A3', etc... Is there a nicer more DRY way of accomplishing this? Edit: There may be values in table 'B' that have no equivalent value for table 'A'.

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• C++ Structure within itself?

  - by Douglas

  I've been trying to port this code to python, but there is something I do not quite understand in C++ (I do know a bit of C++ but this is beyond me): typedef struct huffnode_s { struct huffnode_s *zero; struct huffnode_s *one; unsigned char val; float freq; } huffnode_t; What I don't get is how huffnode_s can be within itself, I've never seen this before and don't quite understand it. What does this mean, and if someone can, what would be the python equivalent?

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• Want to understand C++ sentry object

  - by Romain Hippeau

  I answered this [question][1] and somebody else had answered as he modern C++ equivalent would be a sentry object: construct it at the beginning of a function, with its constructor implementing call(), and upon return (or abnormal exit), its destructor implements I am not familiar with using sentry objects in C++. I thought they were limited to input and output streams. Could somebody explain to me about C++ sentry objects as well as how to use them as an around interceptor for one or more methods in a class ? [1]: http://stackoverflow.com/questions/2688043/call-return-feature-of-classic-cc-with-classes-what-modern-languages-have-it/2688095#2688095 /

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• I want absolute atomicity on a single couchdb instance (insert, fail if already existing)

  - by MatternPatching

  I've come to really love the couchdb style of organizing and updating data, but there are a few situations where I really need to be able to create an entry and determine if an equivalent entry is already in existence before returning to the user. The only situation that this is absolutely necessary for my application is user registration. I'm fine with having all user registration writes go to a particular, designated couchdb instance known as the "registration-instance". I want to hash the user_id into some _id to use. Then execute a put with this _id, but fail if the _id is already inserted. I need to return to the user that the user name is already reserved, and I cannot detect the conflict later and resolve it at that point, because the user would be under the impression that they had reserved the user name. I don't see why couchdb couldn't provide some way to do this, under the assumption that you designate that inserts for a particular "type" of document always are routed to a particular instance.

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• How can I declare a pointer with filled information in C++?

  - by chacham15

  typedef struct Pair_s { char *first; char *second; } Pair; Pair pairs[] = { {"foo", "bar"}, //this is fine {"bar", "baz"} }; typedef struct PairOfPairs_s { Pair *first; Pair *second; } PairOfPairs; PairOfPairs pops[] = { {{"foo", "bar"}, {"bar", "baz"}}, //How can i create an equivalent of this NEATLY {&pairs[0], &pairs[1]} //this is not considered neat (imagine trying to read a list of 30 of these) }; How can I achieve the above style declaration semantics?

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• C++ template typedef

  - by Notinlist

  I have a class template<size_t N, size_t M> class Matrix { // .... }; I want to make a typedef which creates a Vector (column vector) which is equivalent to a Matrix with sizes N and 1. Something like that: typedef Matrix<N,1> Vector<N>; Which produces compile error. The following creates something similar, but not exactly what I want: template <int N> class Vector: public Matrix<N,1> { }; Is there a solution or a not too expensive workaround / best-practice for it? Thanks in advance!

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• Is there a shorthand way to denullify a string in C#?

  - by Moose Factory

  Is there a shorthand way to denullify a string in C#? It would be the equivalent of (if 'x' is a string): string y = x == null ? "" : x; I guess I'm hoping there's some operator that would work something like: string y = #x; Wishful thinking, huh? The closest I've got so far is an extension method on the string class: public static string ToNotNull(this string value) { return value == null ? "" : value; } which allows me to do: string y = x.ToNotNull(); Any improvements on that, anyone?

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• C/C++ memory usage API in Linux/Windows

  - by minjang

  I'd like to obtain memory usage information for both per process and system wide. In Windows, it's pretty easy. GetProcessMemoryInfo and GlobalMemoryStatusEx do these jobs greatly and very easily. For example, GetProcessMemoryInfo gives "PeakWorkingSetSize" of the given process. GlobalMemoryStatusEx returns system wide available memory. However, I need to do it on Linux. I'm trying to find Linux system APIs that are equivalent GetProcessMemoryInfo and GlobalMemoryStatusEx. I found 'getrusage'. However, max 'ru_maxrss' (resident set size) in struct rusage is just zero, which is not implemented. Also, I have no idea to get system-wide free memory. Current workaround for it, I'm using "system("ps -p %my_pid -o vsz,rsz");". Manually logging to the file. But, it's dirty and not convenient to process the data. I'd like to know some fancy Linux APIs for this purpose.

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• Is there an easy way to copy an iterator into a list in Java?

  - by Space_C0wb0y

  I want something like this: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); fooList.addAll(fooIterator); } which should be equivalent to: public void CopyIteratorIntoList(Iterator<Foo> fooIterator) { List<Foo> fooList = new ArrayList<Foo>(); while(fooIterator.hasNext()) fooList.add(fooIterator.next()); } Is there any method in the API to achieve that, or is this the only way?

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• Counting bits set in a .Net BitArray Class

  - by Sam

  I am implementing a library where I am extensively using the .Net BitArray class and need an equivalent to the Java BitSet.Cardinality() method, i.e. a method which returns the number of bits set. I was thinking of implementing it as an extension method for the BitArray class. The trivial implementation is to iterate and count the bits set (like below), but I wanted a faster implementation as I would be performing thousands of set operations and counting the answer. Is there a faster way than the example below? count = 0; for (int i = 0; i < mybitarray.Length; i++) { if (mybitarray [i]) count++; }

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• jQuery: use filter(), but work with both results

  - by Tomalak

  In jQuery, filter() reduces your result to those elements that fulfill a certain condition. This splits the list in two parts. Working with the "good half" of the elements is easy: $("some selector").filter(function() { // determine result... return result; }).each( /* do something */ ); But how can I work with the "other half" of my elements, too - but without doing the equivalent of this: $("some selector").filter(function() { // determine result... return !result; }).each( /* do something */ ); Basically, I'd like to feed two separate /* do something */ parts to a single filter. One for those that match, and one for the others - without having to select and filter twice.

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• Why not System.Void?

  - by Stewart

  I have no practical reason for knowing this answer, but I'm curious anyway... In C#, trying to use System.Void will produce a compilation error: error CS0673: System.Void cannot be used from C# -- use typeof(void) to get the void type object As I understood it, void is simply an alias of System.Void. So, I don't understand why 'System.Void' can't be used directly as you might with 'string' for 'System.String' for example. I would love to read an explanation for this! Incidentally, System.Void can be successfully used with the Mono compiler, instead of Microsoft's .Net, and there it appears equivalent to using the void keyword. This must therefore be a compiler-enforced restriction rather than a CLR restriction, right?

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• Can jQuery's fadeIn work without AJAX?

  - by Thierry Lam

  I'm submitting a form, sometimes I have some messages that I want to show to the user. I want those messages to jQuery fadeIn after they click on the submit button. Is it possible to achieve that if the submission doesn't involve any AJAX? Here's a sample Django/Python code: # View code message = 'feedback to user' # Template <div id="messages">{{ message }}</div> The equivalent PHP code of the above might be: <?php $message = 'feedback to user'; ?> <div id="messages"><?= $message ?></div> I want #messages above to fade in after a POST. How can I achieve that?

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• Running script constantly in background: daemon, lock file with crontab, or simply loop?

  - by Mauritz Hansen

  I have a Perl script that queries a database for a list of files to process processes the files and then exits Upon startup this script creates a file (let's say script.lock), and upon exit it removes this file. I have a crontab entry that runs this script every minute. If the lockfile exists then the script exits, assuming that another instance of itself is running. The above process works fine but I am not very happy with the robustness of this approach. Specifically, if for some reason the script exits prematurely and the lockfile is not removed then a new instance will not execute properly. I would appreciate some advice on the following: Is using the lock file a good approach or is there a better/more robust way to do this? Is using crontab for this a good idea or could I better write an endless loop with sleep()? Should I use the GNU 'daemon' program or the Perl Proc::Daemon module (or some other equivalent) for this?

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• How do I set ORDER BY params using prepared PDO statement?

  - by Marlorn

  I'm having problems using params in the ORDER BY section of my SQL. It doesn't issue any warnings, but prints out nothing. $order = 'columnName'; $direction = 'ASC'; $stmt = $db->prepare("SELECT field from table WHERE column = :my_param ORDER BY :order :direction"); $stmt->bindParam(':my_param', $is_live, PDO::PARAM_STR); $stmt->bindParam(':order', $order, PDO::PARAM_STR); $stmt->bindParam(':direction', $direction, PDO::PARAM_STR); $stmt->execute(); The :my_param works, but not :order or :direction. Is it not being internally escaped correctly? Am I stuck inserting it directly in the SQL? Like so: $order = 'columnName'; $direction = 'ASC'; $stmt = $db->prepare("SELECT * from table WHERE is_live = :is_live ORDER BY $order $direction"); Is there a PDO::PARAM_COLUMN_NAME constant or some equivalent? Thanks!

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• How do I dynamically create Flex 4 AddChild actions for States?

  - by TK Kocheran

  I have an application in which I need to create mx.states.State objects on the fly, as I'm reading external data in order to create the states. Each State only has a single child, so here's my code which I was using to accomplish this: var state:State = new State(); state.name = "a"; state.overrides = [new AddChild(parent, DisplayObject(view))]; this.states.push(state); However, when I actually change a state, I get a runtime error relating to the fact that you can't call addChild on a spark.components.Group component. Is there an equivalent AddElement action for adding elements to a Group during a state change?

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• Flex 3 - Full unicode support fonts and CSS

  - by BS_C3

  Hi! I'm developping a web application that will be used either in Europe or in Asia (specially Japan -Hiragana, Kanji and Katana-, China and Korea). I'm using the following fonts: - ericssonga628.TTF - HelveticaNeueLTStd-Lt.otf - HelveticaNeueLTStd-LtEx.otf - HelveticaNeueLTStd-Bd.otf - HelveticaNeueLTStd-BdEx.otf When I tried to display Japanese characters, I don't get anything. I guess these fonts don't support East Asian characters... Do you know of any equivalent fonts? Also, I was thinking of creating a CSS for each language (or pack of languages) when the user changes the display language. For example, if the user selects "japanese", I'll use the japanese stylesheet. However, how do I switch from a CSS to another? Thanks in advance for your answers. Regards,

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• SQL Server float datatype

  - by Martin Smith

  The documentation for SQL Server Float says Approximate-number data types for use with floating point numeric data. Floating point data is approximate; therefore, not all values in the data type range can be represented exactly. Which is what I expected it to say. If that is the case though why does the following return 'Yes' in SQL Server DECLARE @D float DECLARE @E float set @D = 0.1 set @E = 0.5 IF ((@D + @D + @D + @D +@D) = @E) BEGIN PRINT 'YES' END ELSE BEGIN PRINT 'NO' END but the equivalent C++ program returns "No"? #include <iostream> using namespace std; int main() { float d = 0.1F; float e = 0.5F; if((d+d+d+d+d) == e) { cout << "Yes"; } else { cout << "No"; } }

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• Python - Create a list with initial capacity

  - by Claudiu

  Code like this often happens: l = [] while foo: #baz l.append(bar) #qux This is really slow if you're about to append thousands of elements to your list, as the list will have to constantly be re-initialized to grow. (I understand that lists aren't just wrappers around some array-type-thing, but something more complicated. I think this still applies, though; let me know if not). In Java, you can create an ArrayList with an initial capacity. If you have some idea how big your list will be, this will be a lot more efficient. I understand that code like this can often be re-factored into a list comprehension. If the for/while loop is very complicated, though, this is unfeasible. Is there any equivalent for us python programmers?

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• C++ - Print Out Objects From Set

  - by John Smith

  If I have a C++ set, declaration set personList; with iterator, set::const_iterator location; how can I print out the contents of the set? They are all person objects, and I have overridden the operator<< for Person. The line that errors is: cout << location and it's in a basic for loop. Netbeans gives the following error: proj.cpp:78: error: no match for ‘operator<<’ in ‘std::cout << location’ so it looks like it wants an override for the iterator's <<. Basically, I am taking objects that used to be stored in an array format, but are now in a set. What is the equivalent to cout << array[i] for sets?

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