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• Why is Postgres doing a Hash in this query?

  - by Claudiu

  I have two tables: A and P. I want to get information out of all rows in A whose id is in a temporary table I created, tmp_ids. However, there is additional information about A in the P table, foo, and I want to get this info as well. I have the following query: SELECT A.H_id AS hid, A.id AS aid, P.foo, A.pos, A.size FROM tmp_ids, P, A WHERE tmp_ids.id = A.H_id AND P.id = A.P_id I noticed it going slowly, and when I asked Postgres to explain, I noticed that it combines tmp_ids with an index on A I created for H_id with a nested loop. However, it hashes all of P before doing a Hash join with the result of the first merge. P is quite large and I think this is what's taking all the time. Why would it create a hash there? P.id is P's primary key, and A.P_id has an index of its own.

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• Nested foreach loops for associative array combinations

  - by JohnL

  I have an associative array as follows: $myarray = array('a'=>array(), 'b'=>array(), 'c'=>array(), 'd'=>array()); I want to be able to get all pairs of elements in the array. If it wasn't an associative array, I would use nested for loops, like: for($i=0; $i<count($myarray); $i++) { for($j=$i+1; $j<count($myarray); $j++) { do_something($myarray[$i], $myarray[$j]); } } I have looked at using foreach loops, but as the inner loop goes through ALL elements, some pairs are repeated. Is there a way to do this? Thanks!

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• How SqlDataAdapter works internally?

  - by tigrou

  I wonder how SqlDataAdapter works internally, especially when using UpdateCommand for updating a huge DataTable (since it's usually a lot faster that just sending sql statements from a loop). Here is some idea I have in mind : It creates a prepared sql statement (using SqlCommand.Prepare()) with CommandText filled and sql parameters initialized with correct sql types. Then, it loops on datarows that need to be updated, and for each record, it updates parameters values, and call SqlCommand.ExecuteNonQuery(). It creates a bunch of SqlCommand objects with everything filled inside (CommandText and sql parameters). Several SqlCommands at once are then batched to the server (depending of UpdateBatchSize). It uses some special, low level or undocumented sql driver instructions that allow to perform an update on several rows in a effecient way (rows to update would need to be provided using a special data format and a the same sql query (UpdateCommand here) would be executed against each of these rows).

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• Making bash script to check connectivity and change connection if necessary. Help me improve it?

  - by cypherpunks

  My connection is flaky, however I have a backup one. I made some bash script to check for connectivity and change connection if the present one is dead. Please help me improve them. The scripts almost works, except for not waiting long enough to receive an IP (it cycles to next step in the until loop too quick). Here goes: #!/bin/bash # Invoke this script with paths to your connection specific scripts, for example # ./gotnet.sh ./connection.sh ./connection2.sh until [ -z "$1" ] # Try different connections until we are online... do if eval "ping -c 1 google.com" then echo "we are online!" && break else $1 # Runs (next) connection-script. echo fi shift done echo # Extra line feed. exit 0 And here is an example of the slave scripts: #!/bin/bash ifconfig wlan0 down ifconfig wlan0 up iwconfig wlan0 key 1234567890 iwconfig wlan0 essid example sleep 1 dhclient -1 -nw wlan0 sleep 3 exit 0

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• How do I show the print with AJAX/jQuery?

  - by Doug

  So I'm trying to understand this whole AJAX/jQuery thing. Right now, when I run this PHP script alone, I would have to wait and watch the wheel spin until it's done with the loop and then it will load. while ( $row = mysql_fetch_array($res) ) { postcode_to_storm( $row['Test'] ); $dom = new DOMDocument(); @$dom->loadHTML($result); $xPath = new DOMXPath($dom); $failInvite = 'Rejected'; $findFalse = strpos($result, $failInvite); if ( $findFalse == true ) { $array[$i] = $row['Test']; $i++; echo $array[$i]}; } } Now, how do I use AJAX/jQuery to show echo $array[$i]}; everytime it is invoked instead of waiting for the whole process to complete?

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• Write a recursive function in C that converts a number into a string

  - by user3501779

  I'm studying software engineering, and came across this exercise: it asks to write a recursive function in C language that receives a positive integer and an empty string, and "translates" the number into a string. Meaning that after calling the function, the string we sent would contain the number but as a string of its digits. I wrote this function, but when I tried printing the string, it did print the number I sent, but in reverse. This is the function: void strnum(int n, char *str) { if(n) { strnum(n/10, str+1); *str = n%10 + '0'; } } For example, I sent the number 123 on function call, and the output was 321 instead of 123. I also tried exchanging the two lines within the if statement, and it still does the same. I can't figure out what I did wrong. Can someone help please? NOTE: Use of while and for loop statements is not allowed for the exercise.

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• update each recordset with datareader

  - by knittl

  hi, my situation is the following: i have a datareader and loop over all records returned by a select statement and then call a function with a value from that row. but now i need to update a column in each row, after the function has been called. using a separate update statement seems like a huge overkill. what's the best method to do so? i've heard about dataadapters and datasets—but the only thing i know is that they exist, not how to use them (properly) in this case. platform is c# with sql server

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• How to analyse Dalvik GC behaviour?

  - by HRJ

  I am developing an application on Android. It is a long running application that continuously processes sensor data. While running the application I see a lot of GC messages in the logcat; about one every second. This is most probably because of objects being created and immediately de-referenced in a loop. How do I find which objects are being created and released immediately? All the java heap analysis tools that I have tried(*) are bothered with the counts and sizes of objects on the heap. While they are useful, I am more interested in finding out the site where temporary short-lived objects get created the most. (*) I tried jcat and Eclipse MAT. I couldn't get hat to work on the Android heap-dumps; it complained of an unsupported dump file version.

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• convert std object class to comma seperated string

  - by Kwaasi Djin

  I have an std class object from twitter and i would like to take the ids array values and put them in a php variable $ids where $ids = (15761916,30144785,382747195,19399719). I imagine using a for loop and using phps implode but i'm not sure how to go about it. stdClass Object ( [ids] => Array ( [0] => 15761916 [1] => 30144785 [2] => 382747195 [3] => 19399719 ) [next_cursor] => 0 [next_cursor_str] => 0 [previous_cursor] => 0 [previous_cursor_str] => 0 )

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• Faster way to compare two sets of points in N-dimensional space?

  - by Amit

  List1 contains a high number (~7^10) of N-dimensional points (N <=10), List2 contains the same or fewer number of N-dimensional points (N <=10). My task is this: I want to check which point in List2 is closest (euclidean distance) to a point in List1 for every point in List1 and subsequently perform some operation on it. I have been doing it the simple- the nested loop way when I didn't have more than 50 points in List1, but with 7^10 points, this obviously takes up a lot of time. What is the fastest way to do this? Any concepts from Computational Geometry might help?

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• check whether fgets would block

  - by lv

  Hi, I was just wondering whether in C is it possible to peek in the input buffer or perform similar trickery to know whether a call to fgets would block at a later time. Java allows to do something like that by calling BufferedReader.ready(), this way I can implement console input something like this: while (on && in.ready()) { line = in.readLine(); /* do something with line */ if (!in.ready()) Thread.sleep(100); } this allows an external thread to gracefully shutdown the input loop by setting on to false; I'd like to perform a similar implementation in C without resorting to non portable tricks, I already know I can make a "timed out fgets" under unix by resorting to signals or (better, even though requering to take care of buffering) reimplement it on top of recv/select, but I'd prefer something that would work on windows too. TIA

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• sqrt(int_value + 0.0) ? The point?

  - by Earlz

  Hello, while doing some homework in my very strange C++ book, which I've been told before to throw away, had a very peculiar code segment. I know homework stuff always throws in extra "mystery" to try to confuse you like indenting 2 lines after a single-statement for-loop. But this one I'm confused on because it seems to serve some real-purpose. basically it is like this: int counter=10; ... if(pow(floor(sqrt(counter+0.0)),2) == counter) ... I'm interested in this part especially: sqrt(counter+0.0) Is there some purpose to the +0.0? Is this the poormans way of doing a static cast to a double? Does this avoid some compiler warning on some compiler I do not use? The entire program printed the exact same thing and compiled without warnings on g++ whenever I left out the +0.0 part. Maybe I'm not using a weird enough compiler?

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• Nested pound sign problem

  - by Ray Buechler

  I'm having an issue when I try to nest pound signs in my ColdFusion code. I keep getting the following error message: Invalid CFML construct found on line 57 at column 26. ColdFusion was looking at the following text: # Here is the code: <cfloop index="i" from="1" to="12"> <cfset needRecord.setNeed#i#(#form["need#i#"]#) /> </cfloop> If I run the loop outside the cfset tag like this: <cfloop index="i" from="1" to="12"> needRecord.setNeed#i#(#form["need#i#"]#) </cfloop> The code runs and generates what I would like to generate within the cfset tag. Any idea what I'm doing wrong? Any help would be greatly appreciated.

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• How to retrieve large data from oracle database using vbscript

  - by allenzzzxd

  Hi guys, I'm now working on vbscript to do some test. Actuelly, I want to retrieve a large amount of data from an oracle database, so I write the code like this: sql = "Select * from CORE_DB where MC = '" & mstr & "' " Set myrs = db_execute_query(curConnection, sql) Then I count the rows in myrs,there are 248 rows. So then I do a For loop to retrieve some fields of each row. For k = 0 To db_get_rows_count(myrs) But then I found that the content of the row k when k 133 was always equal to k = 133. So this makes an error. As I think, there may be a limit size of mrys ? Could anyone light me about this? Thanks a lot in advance

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• Is there a better way to do SELECT queries in MySQL and sort them in PHP than this way?

  - by Kent

  I am just learning PHP/MySQL, one this I am having to do a lot is displaying data that was previously inserted into the database out to the user's browser. So I am doing this: $select = mysql_query('SELECT * FROM pages'); while ($return = mysql_fetch_assoc($select)) { $title = $return['title']; $author = $return['author']; $content = $return['content']; } then I can use these variables through out the page. Now, doing it the above way isn't an issue when I only have 3 columns in a database but what if I am dealing with a huge database with many more columns. I have a nagging feeling that the pros do it in some more efficient way where they maybe loop through the table they are selecting from to find all columns it has and associate them with variables automatically. Is that the case? or is the above how you guys do it too?

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• Using pow() for large number

  - by g4ur4v

  I am trying to solve a problem, a part of which requires me to calculate (2^n)%1000000007 , where n<=10^9. But my following code gives me output "0" even for input like n=99. Is there anyway other than having a loop which multilplies the output by 2 every time and finding the modulo every time (this is not I am looking for as this will be very slow for large numbers). #include<stdio.h> #include<math.h> #include<iostream> using namespace std; int main() { unsigned long long gaps,total; while(1) { cin>>gaps; total=(unsigned long long)powf(2,gaps)%1000000007; cout<<total<<endl; } }

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• getting the value of a filter at an arbitrary time

  - by Andiih

  Context: I'm trying to improve the values returned by the iPhone CLLocationManager, although this is a more generally applicable problem. The key is that CLLocationManger returns data on current velocity as and when it feels like it, rather than at a fixed sample rate. I'd like to use a feedback equation to improve accuracy v=(k*v)+(1-k)*currentVelocity where currentVelocity is the speed returned by didUpdateToLocation:fromLocation: and v is the output velocity (and also used for the feedback element). Because of the "as and when" nature of didUpdateToLocation:fromLocation: I could calculate the time interval since it was last called, and do something like for (i=0;i<timeintervalsincelastcalled;i++) v=(k*v)+(1-k)*currentVelocity which would work, but is wasteful of cycles. Especially as I probably want timeintervalsincelastcalled to be measured as 10ths of a second. Is there a way to solve this without the loop ? i.e. rework (integrate?) the formula so I put an interval into the equation and get the same answer as I would have by iteration ?

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• exporting html table multi line columns to excel multi line cells

  - by Passat

  I have a html table in a view MVC4 that I am sending to excel as output. Inside the view page I have some columns that have multiple lines that are built with forloops within the HTML. What's the best way to add the or \r\n so that excel renders it correctly? I have a table and inside I build each row looping thru a recordset. In each row I also loop thru different recordsets to populate columns within each row so that some of the columns may contain more than one value and they should show in different lines in the table that will export to excel.

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• java: communication between threads

  - by TRU7H

  I'm making a little java game in which I would have two threads (well as the FIRST step towards multithreading...), one for the logic and one for the drawing. So my question is: How can I make those two communicating which each other? Requirements: accessing variables and object from a another thread syncing them so they each complete a same number of "loops" in the same time. (the logic calculates and then the another one draws the results and the loop begins again...) So how is this achievable in java? Thanks in advance!

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• DOS Batch file - Copy file based on filename elements

  - by user1848356

  I need to sort alot of files based on their filename. I would like to use a batch file to do it. I do know what I want but I am not sure of the correct syntax. Example of filenames I work with: (They are all in the same directory originally) 2012_W34_Sales_Store001.pdf 2012_W34_Sales_Store002.pdf 2012_W34_Sales_Store003.pdf 2012_November_Sales_Store001.pdf 2012_November_Sales_Store002.pdf 2012_November_Sales_Store003.pdf I would like to extract the information that are located between the "_" signs and put them into a different variable each time. The lenght of the informations contained between the _ signs will be different everytime. Example: var1="2012" var2="W34" (or November) var3="Sales" var4="001" If I am able to do this, I could then copy the files to the appropriate directory using move %var1%_%var2%_%var3%_%var4%.pdf z:\%var3%\%var4%\%var1%\%var2% It would need to loop because I have Store001 to Store050. Also, there are not only Sales report, many others are available. I hope I am clear. Please help me realize this batchfile!

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• How can I use cURL to open multiple URLs simultaneously with PHP?

  - by Rob

  Here is my current code: $SQL = mysql_query("SELECT url FROM urls") or die(mysql_error()); //Query the urls table while($resultSet = mysql_fetch_array($SQL)){ //Put all the urls into one variable // Now for some cURL to run it. $ch = curl_init($resultSet['url']); //load the urls curl_setopt($ch, CURLOPT_TIMEOUT, 2); //No need to wait for it to load. Execute it and go. curl_exec($ch); //Execute curl_close($ch); //Close it off } //While loop I'm relatively new to cURL. By relatively new, I mean this is my first time using cURL. Currently it loads one for two seconds, then loads the next one for 2 seconds, then the next. however, I want to make it load ALL of them at the same time. I'm sure its possible, I'm just unsure as to how. If someone could point me in the right direction, I'd appreciate it.

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• Reusing a vector in C++

  - by Bobby

  I have a vector declared as a global variable that I need to be able to reuse. For example, I am reading multiple files of data, parsing the data to create objects that are then stored in a vector. vector<Object> objVector(100); void main() { while(THERE_ARE_MORE_FILES_TO_READ) { // Pseudocode ReadFile(); ParseFileIntoVector(); ProcessObjectsInVector(); /* Here I want to 'reset' the vector to 100 empty objects again */ } } Can I reset the vector to be "vector objVector(100)" since it was initially allocated on the stack? If I do "objVector.clear()", it removes all 100 objects and I would have a vector with a size of 0. I need it to be a size of 100 at the start of every loop.

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• From xcode not able to execute DISTINCT keyword for sqlite

  - by mac

  -(void) readProductsFromDatabase { // Setup the database object sqlite3 *database; // Init the animals Array products = [[NSMutableArray alloc] init]; // Open the database from the users filessytem if(sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { NSLog(@"db opened"); // Setup the SQL Statement and compile it for faster access const char *sqlStatement = "SELECT DISTINCT productname FROM iphone "; sqlite3_stmt *compiledStatement; if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) { // Loop through the results and add them to the feeds array while(sqlite3_step(compiledStatement) == SQLITE_ROW) { NSLog(@"inside sqlite3 prepare"); // Read the data from the result row NSString *aName = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)]; } } // Release the compiled statement from memory sqlite3_finalize(compiledStatement); } sqlite3_close(database); } My problem is const char *sqlStatement = "SELECT DISTINCT productname FROM iphone "; This line not executing ,i am using sqlite3, thanks in advance,

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• Handling of data truncation (short reads/writes) in FUSE

  - by Vi

  I expect any good program should do all their reads and writes in a loop until all data written/read without relying that write will write everything (even with regular files). Am I right? Implemented simple FUSE filesystem which only allows reading and writing with small buffers, very often returning that it is written less bytes that in a buffer (using -o direct_io). Some programs work, some not (notably mountlo). Are them buggy or programs should not expect truncated writes and reads from the regular files? In general, are seekable file descriptors expected to truncate data like sockets and pipes?

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• Can't catch newConnection() signal from QTcpServer

  - by Bob

  I am trying to make a simple server thread in QT to accept a connection, however although the server is listening (I can connect with my test app) I can't get the newConnection() signal to be acted on. Any help as to what I'm missing here would be much appreciated! class CServerThread : public QThread { Q_OBJECT protected: void run(); private: QTcpServer* server; public slots: void AcceptConnection(); }; void CServerThread::run() { server = new QTcpServer; QObject::connect(server, SIGNAL(newConnection()), this, SLOT(AcceptConnection())); server-listen(QHostAddress::Any, 1000); // Any port in a storm exec(); // Start event loop } void CServerThread::AcceptConnection() { OutputDebugStringA("\n***** INCOMING CONNECTION"); // This is never called! }

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