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• Warning: control reaches end of non-valid function - iPhone

  - by Dave

  I keep getting 'warning: control reaches end of non-void function' with this code: - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { if (section ==0) { return [comparativeList count]; } if (section==1) { return [generalList count]; } if (section==2) { return [contactList count]; How can I get rid of this warning? Thanks.

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• Sql: simultaneous aggregate from two tables

  - by Ash

  I have two tables: a Files table, which includes the file type, and a File Properties table, which references the file table via a foreign key. Sample Files table: | id | name | type | --------------------- | 1 | file1 | zip | | 2 | file2 | zip | | 3 | file3 | zip | | 4 | file4 | jpg | And the Properties table: | file_id | property | ----------------------- | 1 | x | | 2 | x | I want to make a query, which shows the count of each file type, and how many files of that type have a property. So in the example, the result would be | type | filecount | prop count | ---------------------------------- | zip | 3 | 2 | | jpg | 1 | 0 | I could accomplish this by select f.type, (select count(id) from files where type = f.type), count(fp.id) from files as f, file_properties as fp where f.id = fp.file_id group by f.type; But this seems very suboptimal and is very slow. Any better way to do this?

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• Model class for NSDictionary information with Lazy Loading

  - by samfu_1

  My application utilizes approx. 50+ .plists that are used as NSDictionaries. Several of my view controllers need access to the properties of the dictionaries, so instead of writing duplicate code to retrieve the .plist, convert the values to a dictionary, etc, each time I need the info, I thought a model class to hold the data and supply information would be appropriate. The application isn't very large, but it does handle a good deal of data. I'm not as skilled in writing model classes that conform to the MVC paradigm, and I'm looking for some strategies for this implementation that also supports lazy loading.. This model class should serve to supply data to any view controller that needs it and perform operations on the data (such as adding entries to dictionaries) when requested by the controller functions currently planned: returning the count on any dictionary adding one or more dictionaries together Currently, I have this method for supporting the count lookup for any dictionary. Would this be an example of lazy loading? -(NSInteger)countForDictionary: (NSString *)nameOfDictionary { NSBundle *bundle = [NSBundle mainBundle]; NSString *plistPath = [bundle pathForResource: nameOfDictionary ofType: @"plist"]; //load plist into dictionary NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] initWithContentsOfFile: plistPath]; NSInteger count = [dictionary count] [dictionary release]; [return count] }

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• Google Maps API v3 - infoWindows all have same content

  - by paulriedel

  Hello, I've been having problems with the infoWindows and Google Maps API v3. Initially, I've ran into the problem that everyone else has of closing infoWindows when opening a new one. I thought to have solved the problem by defining "infowindow" beforehand. Now they close when I click on a new marker, but the content is the same. How should I re-structure my code to make sure the content is the right one each time - and only one infoWindow is open at a given time? Thank you! Paul var allLatLngs = new Array(); var last = 0; var infowindow; function displayResults(start, count){ if(start === undefined){ start = last; } if(count === undefined){ count = 20; } jQuery.each(jsresults, function(index, value) { if(index >= start && index < start+count){ var obj = jQuery.parseJSON(value); $("#textresults").append(index + ": <strong>" + obj.name + "</strong> " + Math.round(obj.distanz*100)/100 + " km entfernt" + "<br/>"); var myLatlng = new google.maps.LatLng(obj.geo_lat, obj.geo_lon); allLatLngs.push(myLatlng); var contentString = '<strong>'+obj.name+'</strong>'; infowindow = new google.maps.InfoWindow({ content: contentString }); var marker = new google.maps.Marker({ position: myLatlng, //title:"Hello World!" }); marker.setMap(map); google.maps.event.addListener(marker, 'click', function() { if (infowindow) { infowindow.close(map,marker); } infowindow.open(map,marker); }); } }); last = start+count;

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• Check variable if explode-able in PHP

  - by ZaneDeFazio

  Not sure if there is a way to check a variable if it is explode-able or not... I have a database of city names some are one word cities and some are multiple word cities EX: Chicago, Los Angeles I keep getting an error when use "implode" when a city name is one word, so I tried using "count" and using an if statement... not having any luck $citi = explode(' ', $row['city']); $count = count($citi); if ($count > 1) { $city = implode('+', $citi); } else { $city = $citi; }

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• Appending unique values only in a linked list in C

  - by LuckySlevin

  typedef struct child {int count; char word[100]; inner_list*next;} child; typedef struct parent { char data [100]; inner_list * head; int count; outer_list * next; } parent; void append(child **q,char num[100],int size) { child *temp,*r,*temp2,*temp3; parent *out=NULL; temp = *q; temp2 = *q; temp3 = *q; char *str; if(*q==NULL) { temp = (child *)malloc(sizeof(child)); strcpy(temp->word,num); temp->count =size; temp->next=NULL; *q=temp; } else { temp = *q; while(temp->next !=NULL) { temp=temp->next; } r = (child *)malloc(sizeof(child)); strcpy(r->word,num); r->count = size; r->next=NULL; temp->next=r; } } This is my append function which I use for adding an element to my child list. But my problem is it only should append unique values which are followed by a string. Which means : Inputs : aaa bbb aaa ccc aaa bbb ccc aaa Append should act : For aaa string there should be a list like bbb->ccc(Not bbb->ccc->bbb since bbb is already there if bbb is coming more than one time it should be increase count only.) For bbb string there should be list like aaa->ccc only For ccc string there should be list like aaa only I hope i could make myself clear. Is there any ideas? Please ask for further info.

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• aggregate over several variables in r

  - by Misha

  Dear overflowers, I have a rather large dataset in a long format where I need to count the number of instances of the ID due to two different variables, A & B. E.g. The same person can be represented in multiple rows due to either A or B. What I need to do is to count the number of instances of ID which is not too hard, but also count the number of ID due to A and B and return these as variables in the dataset. Regards, //Mi

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• Why is this MySQL INSERT INTO running twice?

  - by stuboo

  I'm attempting to use the mysql insert statement below to add information to a database table. When I execute the script, however, the insert statement is run twice. Here's the URL mysite.com/save.php?Body=p220,c180 Thanks in advance. <?php //tipping fees application require('base.inc.php'); require('functions.inc.php'); // connect to the database & save this message there try { $dbh = new PDO("mysql:host=$dbhost;dbname=$dbname", $dbuser, $dbpass); //$number = formatPhone($_REQUEST['From']); //if($number != 'xxx-xxx-xxxx'){die('SMS from unknown number');} // kill this if from anyone but mike $message = $_REQUEST['Body']; //$Sid = $_REQUEST['SmsSid']; $now = time(); echo $message; $message = explode(",",$message); echo '<pre>'; print_r($message); echo 'message count = '.count($message); echo '</pre>'; $i = 0; $j = count($message); while($i<$j){ $quantity =$message[$i]; $material = substr($quantity, 0, 1); $amount = substr($quantity, 1); switch ($material) { case 'p': $m = "paper"; break; case 'c': $m = "containers"; break; default: $m = "other"; } $count = $dbh->exec("INSERT INTO tippingtotals(sid,time,material,weight) VALUES('$i+$j','$now','$m','$amount')"); echo $count; echo '<br />'; $i++; } //close the database connection $dbh = null; } catch(PDOException $e) { echo $e->getMessage(); } ?>

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• Does Table.InsertOnSubmit create a copy of the original table?

  - by Bryan

  Using InsertOnSubmit seems to have some memory overhead. I have a System.Data.Linq.Table<User> table. When I do table.InsertOnSubmit(user) and then int count = table.Count(), the memory usage of my application increases by roughly the size of the User table, but the count is the number of items before user was inserted. So I'm guess an enumeration after InsertOnSubmit will create a copy of the table. Is that true?

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• How to calculate siteamps priority value based on views?

  - by stacker

  How can I calculate sitemap url priority based on the views count of the article / comments count?

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• Fill container with template parameters

  - by phlipsy

  I want to fill the template parameters passed to a variadic template into an array with fixed length. For that purpose I wrote the following helper function templates template<typename ForwardIterator, typename T> void fill(ForwardIterator i) { } template<typename ForwardIterator, typename T, T head, T... tail> void fill(ForwardIterator i) { *i = head; fill<ForwardIterator, T, tail...>(++i); } the following class template template<typename T, T... args> struct params_to_array; template<typename T, T last> struct params_to_array<T, last> { static const std::size_t SIZE = 1; typedef std::array<T, SIZE> array_type; static const array_type params; private: void init_params() { array_type result; fill<typename array_type::iterator, T, head, tail...>(result.begin()); return result; } }; template<typename T, T head, T... tail> struct params_to_array<T, head, tail...> { static const std::size_t SIZE = params_to_array<T, tail...>::SIZE + 1; typedef std::array<T, SIZE> array_type; static const array_type params; private: void init_params() { array_type result; fill<typename array_type::iterator, T, last>(result.begin()); return result; } }; and initialized the static constants via template<typename T, T last> const typename param_to_array<T, last>::array_type param_to_array<T, last>::params = param_to_array<T, last>::init_params(); and template<typename T, T head, T... tail> const typename param_to_array<T, head, tail...>::array_type param_to_array<T, head, tail...>::params = param_to_array<T, head, tail...>::init_params(); Now the array param_to_array<int, 1, 3, 4>::params is a std::array<int, 3> and contains the values 1, 3 and 4. I think there must be a simpler way to achieve this behavior. Any suggestions? Edit: As Noah Roberts suggested in his answer I modified my program like the following: I wrote a new struct counting the elements in a parameter list: template<typename T, T... args> struct count; template<typename T, T head, T... tail> struct count<T, head, tail...> { static const std::size_t value = count<T, tail...>::value + 1; }; template<typename T, T last> stuct count<T, last> { static const std::size_t value = 1; }; and wrote the following function template<typename T, T... args> std::array<T, count<T, args...>::value> params_to_array() { std::array<T, count<T, args...>::value> result; fill<typename std::array<T, count<T, args...>::value>::iterator, T, args...>(result.begin()); return result; } Now I get with params_to_array<int, 10, 20, 30>() a std::array<int, 3> with the content 10, 20 and 30. Any further suggestions?

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• Does Interlocked guarantee visibility to other threads in C# or do I still have to use volatile?

  - by Lirik

  I've been reading the answer to a similar question, but I'm still a little confused... Abel had a great answer, but this is the part that I'm unsure about: ...declaring a variable volatile makes it volatile for every single access. It is impossible to force this behavior any other way, hence volatile cannot be replaced with Interlocked. This is needed in scenarios where other libraries, interfaces or hardware can access your variable and update it anytime, or need the most recent version. Does Interlocked guarantee visibility of the atomic operation to all threads, or do I still have to use the volatile keyword on the value in order to guarantee visibility of the change? Here is my example: public class CountDownLatch { private volatile int m_remain; // <--- do I need the volatile keyword there since I'm using Interlocked? private EventWaitHandle m_event; public CountDownLatch (int count) { Reset(count); } public void Reset(int count) { if (count < 0) throw new ArgumentOutOfRangeException(); m_remain = count; m_event = new ManualResetEvent(false); if (m_remain == 0) { m_event.Set(); } } public void Signal() { // The last thread to signal also sets the event. if (Interlocked.Decrement(ref m_remain) == 0) m_event.Set(); } public void Wait() { m_event.WaitOne(); } }

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• fgets, sscanf, and writing to arrays

  - by alldavidsluck

  beginner question here, I haven't been able to find examples that relate. I'm working on a C program that will take integer input from stdin using fgets and sscanf, and then write it to an array. However, I'm not sure how to make fgets write to the array. #define MAXINT 512 char input[MAXINT] int main(void) { int i; int j; int count=0; int retval; while (1==1) { fgets(input, MAXINT[count], stdin); retval = sscanf(input, "%d", &i); if (retval == 1) { count = count++; } else if (retval != 1) { break; } } Would I simply put fgets in a for loop? or is it more complicated than that?

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• Sql Server 2005 multiple insert with c#

  - by bottlenecked

  Hello. I have a class named Entry declared like this: class Entry{ string Id {get;set;} string Name {get;set;} } and then a method that will accept multiple such Entry objects for insertion into the database using ADO.NET: static void InsertEntries(IEnumerable<Entry> entries){ //build a SqlCommand object using(SqlCommand cmd = new SqlCommand()){ ... const string refcmdText = "INSERT INTO Entries (id, name) VALUES (@id{0},@name{0});"; int count = 0; string query = string.Empty; //build a large query foreach(var entry in entries){ query += string.Format(refcmdText, count); cmd.Parameters.AddWithValue(string.Format("@id{0}",count), entry.Id); cmd.Parameters.AddWithValue(string.Format("@name{0}",count), entry.Name); count++; } cmd.CommandText=query; //and then execute the command ... } } And my question is this: should I keep using the above way of sending multiple insert statements (build a giant string of insert statements and their parameters and send it over the network), or should I keep an open connection and send a single insert statement for each Entry like this: using(SqlCommand cmd = new SqlCommand(){ using(SqlConnection conn = new SqlConnection(){ //assign connection string and open connection ... cmd.Connection = conn; foreach(var entry in entries){ cmd.CommandText= "INSERT INTO Entries (id, name) VALUES (@id,@name);"; cmd.Parameters.AddWithValue("@id", entry.Id); cmd.Parameters.AddWithValue("@name", entry.Name); cmd.ExecuteNonQuery(); } } } What do you think? Will there be a performance difference in the Sql Server between the two? Are there any other consequences I should be aware of? Thank you for your time!

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• Help needed with simple mysql group by query

  - by Jack

  This query fails when I add the line shown... :BEGIN FAIL: I have this so far Select Companyid, count(*) as cnt from mytable where State is not null and cnt = 1 <------------------------- FAIL group by CompanyID :END FAIL: Any way to do this? Here's a long winded background if it'll help.... I have a single table query. here's a sample of the table: CompanyID, State 1,OH 1,IL 1,NY 2,IL 3,NY 3,OH 4,NY 5,CA 5,WA I want a query that'll return something like this: 2,IL 4,NY I have this so far Select Companyid, count(*) as cnt from mytable where State is not null group by CompanyID This gives me a count of the number of records for each company. IE: 1,3 2,1 3,2 4,1 5,2 Now I want to filter the above list to just the two records with one result. I tried adding another where clause, but it failed: BEGIN FAIL: I have this so far Select Companyid, count(*) as cnt from mytable where State is not null and cnt = 1 <-------------------- FAIL group by CompanyID END FAIL:

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• Javascript: find first n prime numbers

  - by bard

  function primeNumbers() { array = []; for (var i = 2; array.length < 100; i++) { for (var count = 2; count < i; count++) { var divisorFound = false; if (i % count === 0) { divisorFound = true; break; } } if (divisorFound == false) {array.push[i];} } return array; } When I run this code, it seems to get stuck in an infinite loop and doesn't return anything... why?

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• How do you automatically refresh part of a page automatically using Javascript or AJAX?

  - by Ryan

  $messages = $db->query("SELECT * FROM chatmessages ORDER BY datetime DESC, displayorderid DESC LIMIT 0,10"); while($message = $db->fetch_array($messages)) { $oldmessages[] = $message['message']; } $oldmessages = array_reverse($oldmessages); ?> <div id="chat"> <?php for ($count = 0; $count < 9; $count++) { echo $oldmessages[$count]; } ?> <script language="javascript" type="text/javascript"> <!-- setInterval( "document.getElementById('chat').innerHTML='<NEW CONTENT OF #CHAT>'", 1000 ); --> </script> </div> I'm trying to create a PHP chatroom script but I'm having a lot of trouble getting it to AutoRefresh The content should automatically update to , how do you make it do that? I've been searching for almost an hour

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• PHP Readfile() number of bytes when user aborted

  - by jtnire

  Hi Everyone, I'm using a PHP script to stream a live video (i.e. a file which never ends) from a remote source. The output is viewed in VLC, not a web browser. I need to keep a count of the number of bytes transferred. Here is my code: <?php ignore_user_abort(true); $stream = $_GET['stream']; if($stream == "vid1") { $count = readfile('http://127.0.0.1:8080/'); logThis($count); } function logThis($c) { $myFile = "bytecount.txt"; $handle = fopen($myFile,'a'); fwrite($handle,"Count: " . $c . "\n"); fclose($handle); } ?> However it appears that when the user presses the stop button, logThis() is never called, even though I've put in ignore_user_abort(true); Any ideas on what I'm doing wrong? Thanks

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• Nested WHILE loops not acting as expected - Javascript / Google Apps Script

  - by dthor

  I've got a function that isn't acting as intended. Before I continue, I'd like preface this with the fact that I normally program in Mathematica and have been tasked with porting over a Mathematica function (that I wrote) to JavaScript so that it can be used in a Google Docs spreadsheet. I have about 3 hours of JavaScript experience... The entire (small) project is calculating the Gross Die per Wafer, given a wafer and die size (among other inputs). The part that isn't working is where I check to see if any corner of the die is outside of the effective radius, Reff. The function takes a list of X and Y coordinates which, when combined, create the individual XY coord of the center of the die. That is then put into a separate function "maxDistance" that calculates the distance of each of the 4 corners and returns the max. This max value is checked against Reff. If the max is inside the radius, 1 is added to the die count. // Take a list of X and Y values and calculate the Gross Die per Wafer function CoordsToGDW(Reff,xSize,ySize,xCoords,yCoords) { // Initialize Variables var count = 0; // Nested loops create all the x,y coords of the die centers for (var i = 0; i < xCoords.length; i++) { for (var j = 0; j < yCoords.length, j++) { // Add 1 to the die count if the distance is within the effective radius if (maxDistance(xCoords[i],yCoords[j],xSize,ySize) <= Reff) {count = count + 1} } } return count; } Here are some examples of what I'm getting: xArray={-52.25, -42.75, -33.25, -23.75, -14.25, -4.75, 4.75, 14.25, 23.75, 33.25, 42.75, 52.25, 61.75} yArray={-52.5, -45.5, -38.5, -31.5, -24.5, -17.5, -10.5, -3.5, 3.5, 10.5, 17.5, 24.5, 31.5, 38.5, 45.5, 52.5, 59.5} CoordsToGDW(45,9.5,7.0,xArray,yArray) returns: 49 (should be 72) xArray={-36, -28, -20, -12, -4, 4, 12, 20, 28, 36, 44} yArray={-39, -33, -27, -21, -15, -9, -3, 3, 9, 15, 21, 27, 33, 39, 45} CoordsToGDW(32.5,8,6,xArray,yArray) returns: 39 (should be 48) I know that maxDistance() is returning the correct values. So, where's my simple mistake? Also, please forgive me writing some things in Mathematica notation... Edit #1: A little bit of formatting. Edit #2: Per showi, I've changed WHILE loops to FOR loops and replaced <= with <. Still not the right answer. It did clean things up a bit though... Edit #3: What I'm essentially trying to do is take [a,b] and [a,b,c] and return [[a,a],[a,b],[a,c],[b,a],[b,b],[b,c]]

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• Oracle Rows into Columns

  - by user2904845

  Can someone help me design the query to get below o/p. Data I have: Table X: Count Name Amount Days 5 ABC 500 Day1 10 ABC 1000 Day2 3 BCD 100 Day1 4 BDC 200 Day2 Result I need: Name Count AmountDay1 Count AmountDay2 ABC 5 500 10 1000 BCD 3 100 4 200 etc Is this Possible? I tried something with the below query, but not getting the desired o/p select * from X pivot (sum(amount) for days in ('Day1', 'Day2')) Please help I'm using Oracle 11 G

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• Linked lists in Java - Help with writing methods

  - by user368241

  Representation of a string in linked lists In every intersection in the list there will be 3 fields : The letter itself. The number of times it appears consecutively. A pointer to the next intersection in the list. The following class CharNode represents a intersection in the list : public class CharNode { private char _data; private int _value; private charNode _next; public CharNode (char c, int val, charNode n) { _data = c; _value = val; _next = n; } public charNode getNext() { return _next; } public void setNext (charNode node) { _next = node; } public int getValue() { return _value; } public void setValue (int v) { value = v; } public char getData() { return _data; } public void setData (char c) { _data = c; } } The class StringList represents the whole list : public class StringList { private charNode _head; public StringList() { _head = null; } public StringList (CharNode node) { _head = node; } } Add methods to the class StringList according to the details : (I will add methods gradually according to my specific questions) (Pay attention, these are methods from the class String and we want to fulfill them by the representation of a string by a list as explained above) Pay attention to all the possible error cases. Write what is the time complexity and space complexity of every method that you wrote. Make sure the methods you wrote are effective. It is NOT allowed to use ready classes of Java. It is NOT allowed to move to string and use string operations. 1) public int indexOf (int ch) - returns the index in the string it is operated on of the first appeareance of the char "ch". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex isn't in the range, returns -1. Here is my try : public int indexOf (int ch) { int count = 0; charNode pos = _head; if (pos == null ) { return -1; } for (pos = _head; pos!=null && pos.getData()!=ch; pos = pos.getNext()) { count = count + pos.getValue(); } if (pos==null) return -1; return count; } Time complexity = O(N) Space complexity = O(1) EDIT : I have a problem. I tested it in BlueJ and if the char ch doesn't appear it returns -1 but if it does, it always returns 0 and I don't understand why... I am confused. How can the compiler know that the value is the number of times the letter appears consecutively? Can I assume this because its given on the question or what? If it's true and I can assume this, then my code should be correct right? Ok I just spoke with my instructor and she said it isn't required to write it in the exercise but in order for me to test that it indeed works, I need to open a new class and write a code for making a list so that the the value of every node is the number of times the letter appears consecutively. Can someone please assist me? So I will copy+paste to BlueJ and this way I will be able to test all the methods. Meanwhile I am moving on to the next methods. 2) public int indexOf (int ch, int fromIndex) - returns the index in the string it is operated on of the first appeareance of the char "ch", as the search begins in the index "fromIndex". If the char "ch" doesn't appear in the string, returns -1. If the value of fromIndex doesn't appear in the range, returns -1. Here is my try: public int indexOf (int ch, int fromIndex) { int count = 0, len=0, i; charNode pos = _head; CharNode cur = _head; for (pos = _head; pos!=null; pos = pos.getNext()) { len = len+1; } if (fromIndex<0 || fromIndex>=len) return -1; for (i=0; i<fromIndex; i++) { cur = cur.getNext(); } if (cur == null ) { return -1; } for (cur = _head; cur!=null && cur.getData()!=ch; cur = cur.getNext()) { count = count + cur.getValue(); } if (cur==null) return -1; return count; } Time complexity = O(N) ? Space complexity = O(1) 3) public StringList concat (String str) - returns a string that consists of the string that it is operated on and in its end the string "str" is concatenated. Here is my try : public StringList concat (String str) { String str = ""; charNode pos = _head; if (str == null) return -1; for (pos = _head; pos!=null; pos = pos.getNext()) { str = str + pos.getData(); } str = str + "str"; return str; } Time complexity = O(N) Space complexity = O(1)

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• Counting in R data.table

  - by Simon Z.

  I have the following data.table set.seed(1) DT <- data.table(VAL = sample(c(1, 2, 3), 10, replace = TRUE)) VAL 1: 1 2: 2 3: 2 4: 3 5: 1 6: 3 7: 3 8: 2 9: 2 10: 1 Now I want to to perform two tasks: Count the occurrences of numbers in VAL. Count within all rows with the same value VAL (first, second, third occurrence) At the end I want the result VAL COUNT IDX 1: 1 3 1 2: 2 4 1 3: 2 4 2 4: 3 3 1 5: 1 3 2 6: 3 3 2 7: 3 3 3 8: 2 4 3 9: 2 4 4 10: 1 3 3 where COUNT defines task 1. and IDX task 2. I tried to work with which and length using .I: dt[, list(COUNT = length(VAL == VAL[.I]), IDX = which(which(VAL == VAL[.I]) == .I))] but this does not work as .I refers to a vector with the index, so I guess one must use .I[]. Though inside .I[] I again face the problem, that I do not have the row index and I do know (from reading data.table FAQ and following the posts here) that looping through rows should be avoided if possible. So, what's the data.table way?

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• Faster quadrature decoder loops with Python code

  - by Kelei

  I'm working with a BeagleBone Black and using Adafruit's IO Python library. Wrote a simple quadrature decoding function and it works perfectly fine when the motor runs at about 1800 RPM. But when the motor runs at higher speeds, the code starts missing some of the interrupts and the encoder counts start to accumulate errors. Do you guys have any suggestions as to how I can make the code more efficient or if there are functions which can cycle the interrupts at a higher frequency. Thanks, Kel Here's the code: # Define encoder count function def encodercount(term): global counts global Encoder_A global Encoder_A_old global Encoder_B global Encoder_B_old global error Encoder_A = GPIO.input('P8_7') # stores the value of the encoders at time of interrupt Encoder_B = GPIO.input('P8_8') if Encoder_A == Encoder_A_old and Encoder_B == Encoder_B_old: # this will be an error error += 1 print 'Error count is %s' %error elif (Encoder_A == 1 and Encoder_B_old == 0) or (Encoder_A == 0 and Encoder_B_old == 1): # this will be clockwise rotation counts += 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) elif (Encoder_A == 1 and Encoder_B_old == 1) or (Encoder_A == 0 and Encoder_B_old == 0): # this will be counter-clockwise rotation counts -= 1 print 'Encoder count is %s' %counts print 'AB is %s %s' % (Encoder_A, Encoder_B) else: #this will be an error as well error += 1 print 'Error count is %s' %error Encoder_A_old = Encoder_A # store the current encoder values as old values to be used as comparison in the next loop Encoder_B_old = Encoder_B # Initialize the interrupts - these trigger on the both the rising and falling GPIO.add_event_detect('P8_7', GPIO.BOTH, callback = encodercount) # Encoder A GPIO.add_event_detect('P8_8', GPIO.BOTH, callback = encodercount) # Encoder B # This is the part of the code which runs normally in the background while True: time.sleep(1)

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• Printing out variables in c changes values of variables

  - by George Wilson

  I have an odd problem with some c-programme here. I was getting some wrong values in a matrix I was finding the determinant of and so I started printing variables - yet found that by printing values out the actual values in the code changed. I eventually narrowed it down to one specific printf statement - highlighted in the code below. If I comment out this line then I start getting incorrect values in my determinent calculations, yet by printing it out I get the value out I expect Code below: #include <math.h> #include <stdio.h> #include <stdlib.h> #define NUMBER 15 double determinant_calculation(int size, double array[NUMBER][NUMBER]); int main() { double array[NUMBER][NUMBER], determinant_value; int size; array[0][0]=1; array[0][1]=2; array[0][2]=3; array[1][0]=4; array[1][1]=5; array[1][2]=6; array[2][0]=7; array[2][1]=8; array[2][2]=10; size=3; determinant_value=determinant_calculation(size, array); printf("\n\n\n\n\n\nDeterminant value is %lf \n\n\n\n\n\n", determinant_value); return 0; } double determinant_calculation(int size, double array[NUMBER][NUMBER]) { double determinant_matrix[NUMBER][NUMBER], determinant_value; int x, y, count=0, sign=1, i, j; /*initialises the array*/ for (i=0; i<(NUMBER); i++) { for(j=0; j<(NUMBER); j++) { determinant_matrix[i][j]=0; } } /*does the re-cursion method*/ for (count=0; count<size; count++) { x=0; y=0; for (i=0; i<size; i++) { for(j=0; j<size; j++) { if (i!=0&&j!=count) { determinant_matrix[x][y]=array[i][j]; if (y<(size-2)) { y++; } else { y=0; x++; } } } } //commenting this for loop out changes the values of the code determinent prints -7 when commented out and -3 (expected) when included! for (i=0; i<size; i++) { for(j=0; j<size; j++){ printf("%lf ", determinant_matrix[i][j]); } printf("\n"); } if(size>2) { determinant_value+=sign*(array[0][count]*determinant_calculation(size-1 ,determinant_matrix)); } else { determinant_value+=sign*(array[0][count]*determinant_matrix[0][0]); } sign=-1*sign; } return (determinant_value); } I know its not the prettiest (or best way) of doing what I'm doing with this code but it's what I've been given - so can't make huge changes. I don't suppose anyone could explain why printing out the variables can actually change the values? or how to fix it because ideally i don't want to!!

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• How to invert alternate bits of a number

  - by Cupidvogel

  The problem is how to invert alternate bits of a number, starting from the LSB. Currently what I am doing is first doing a count = -1 while n: n >>= 1 count += 1 to first find the position of the leftmost set bit, then running a loop to invert every alternate bit: i = 0 while i <= count: num ^= 1<<i i += 2 Is there a quick hack solution instead of this rather boring loop solution? Of course, the solution can't make any asumption about the size of the integer.

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