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  • What statistics can be maintained for a set of numerical data without iterating?

    - by Dan Tao
    Update Just for future reference, I'm going to list all of the statistics that I'm aware of that can be maintained in a rolling collection, recalculated as an O(1) operation on every addition/removal (this is really how I should've worded the question from the beginning): Obvious Count Sum Mean Max* Min* Median** Less Obvious Variance Standard Deviation Skewness Kurtosis Mode*** Weighted Average Weighted Moving Average**** OK, so to put it more accurately: these are not "all" of the statistics I'm aware of. They're just the ones that I can remember off the top of my head right now. *Can be recalculated in O(1) for additions only, or for additions and removals if the collection is sorted (but in this case, insertion is not O(1)). Removals potentially incur an O(n) recalculation for non-sorted collections. **Recalculated in O(1) for a sorted, indexed collection only. ***Requires a fairly complex data structure to recalculate in O(1). ****This can certainly be achieved in O(1) for additions and removals when the weights are assigned in a linearly descending fashion. In other scenarios, I'm not sure. Original Question Say I maintain a collection of numerical data -- let's say, just a bunch of numbers. For this data, there are loads of calculated values that might be of interest; one example would be the sum. To get the sum of all this data, I could... Option 1: Iterate through the collection, adding all the values: double sum = 0.0; for (int i = 0; i < values.Count; i++) sum += values[i]; Option 2: Maintain the sum, eliminating the need to ever iterate over the collection just to find the sum: void Add(double value) { values.Add(value); sum += value; } void Remove(double value) { values.Remove(value); sum -= value; } EDIT: To put this question in more relatable terms, let's compare the two options above to a (sort of) real-world situation: Suppose I start listing numbers out loud and ask you to keep them in your head. I start by saying, "11, 16, 13, 12." If you've just been remembering the numbers themselves and nothing more, and then I say, "What's the sum?", you'd have to think to yourself, "OK, what's 11 + 16 + 13 + 12?" before responding, "52." If, on the other hand, you had been keeping track of the sum yourself while I was listing the numbers (i.e., when I said, "11" you thought "11", when I said "16", you thought, "27," and so on), you could answer "52" right away. Then if I say, "OK, now forget the number 16," if you've been keeping track of the sum inside your head you can simply take 16 away from 52 and know that the new sum is 36, rather than taking 16 off the list and them summing up 11 + 13 + 12. So my question is, what other calculations, other than the obvious ones like sum and average, are like this? SECOND EDIT: As an arbitrary example of a statistic that (I'm almost certain) does require iteration -- and therefore cannot be maintained as simply as a sum or average -- consider if I asked you, "how many numbers in this collection are divisible by the min?" Let's say the numbers are 5, 15, 19, 20, 21, 25, and 30. The min of this set is 5, which divides into 5, 15, 20, 25, and 30 (but not 19 or 21), so the answer is 5. Now if I remove 5 from the collection and ask the same question, the answer is now 2, since only 15 and 30 are divisible by the new min of 15; but, as far as I can tell, you cannot know this without going through the collection again. So I think this gets to the heart of my question: if we can divide kinds of statistics into these categories, those that are maintainable (my own term, maybe there's a more official one somewhere) versus those that require iteration to compute any time a collection is changed, what are all the maintainable ones? What I am asking about is not strictly the same as an online algorithm (though I sincerely thank those of you who introduced me to that concept). An online algorithm can begin its work without having even seen all of the input data; the maintainable statistics I am seeking will certainly have seen all the data, they just don't need to reiterate through it over and over again whenever it changes.

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  • Need help with SQL query on SQL Server 2005

    - by Avinash
    We're seeing strange behavior when running two versions of a query on SQL Server 2005: version A: SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = 1234 ORDER BY name ASC version B: DECLARE @Id AS INT; SET @Id = 1234; SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @Id ORDER BY name ASC Both queries return 1000 rows; version A takes on average 15s; version B on average takes 4s. Could anyone help us understand the difference in execution times of these two versions of SQL? If we invoke this query via named parameters using NHibernate, we see the following query via SQL Server profiler: EXEC sp_executesql N'SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @id ORDER BY name ASC', N'@id INT', @id=1234; ...and this tends to perform as badly as version A.

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  • ISBNdb Retrieving and Managing Info

    - by Pierre Sylvestre
    Given a set of databases how can one you get information on a book with given price first (which consist of the average of a hidden list of prices coming from different web site) and followed by an optional second option that shows the list of the different web site with their page? To take an example given a query for ISBN 9785554443331 - it returns "Chemistry the central science 11 edition" : new:$50 used good condition:$35 used poor condition:$20 If the return does not match with our product list an option to "click here to visit our partner" appears and which returns: Atextbook: $10 Btextbook: $10 Ctextbook: $9 Dtextbook: $8.50 I understand that the first search would be done simultaneous on the web and our database to determine whether or not we have the book and the web to get the average of the price of a given list of web site. Thank you in advance for the help

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  • min() and max() give error: TypeError: 'float' object is not iterable

    - by PythonUser3.3
    markList=[] Lmark=0 Hmark=0 while True: mark=float(input("Enter your marks here(Click -1 to exit)")) if mark == -1: break markList.append(mark) markList.sort() mid = len(markList)//2 if len(markList)%2==0: median=(markList[mid]+ markList[mid-1])/2 print("Median:", median) else: print("Median:" , markList[mid]) Lmark==(min(mark)) print("The lowest mark is", Lmark) Hmark==(max(mark)) print("The highest mark is", Hmark) My program is a basic grade calculator using lists. My program asks the user to input their grades into a list in which it then calculates your average and finds your lowest and highest mark. I have found the average but I can't seem to figure out how to find the lowest and highest grade. Can you please show me pr tell me what to do?

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  • Performance optimization for SQL Server: decrease stored procedures execution time or unload the ser

    - by tim
    We have a web service which provides search over hotels. There is a problem with performance: a single request to the service takes around 5000 ms. Almost all of the time is spent in database by executing storing procedures. During the request our server (mssql2008) consumes ~90% of the processor time. When 2 requests are made in parallel the average time grows and is around 7000 ms. When number of request is increasing, the average time of response is increasing as well. We have 20-30 requests per minute. Which kind of optimization is the best in this case having in mind that the goal is to provide stable response time for the service: 1) Try to decrease the stored procedures execution time 2) Try to find the way how to unload the server It is interesting to hear from people who deal with booking sites.

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  • AVG time spent on multiple rows SQL-server?

    - by seo20
    I have a table tblSequence with 3 cols in MS SQL: ID, IP, [Timestamp] Content could look like this: ID IP [Timestamp] -------------------------------------------------- 4347 62.107.95.103 2010-05-24 09:27:50.470 4346 62.107.95.103 2010-05-24 09:27:45.547 4345 62.107.95.103 2010-05-24 09:27:36.940 4344 62.107.95.103 2010-05-24 09:27:29.347 4343 62.107.95.103 2010-05-24 09:27:12.080 ID is unique, there can be n number of IP's. Would like to calculate the average time spent per IP. in a single row Know you can do something like this: SELECT CAST(AVG(CAST(MyTable.MyDateTimeFinish - MyTable.MyDateTimeStart AS float)) AS datetime) But how on earth do I find the first and last entry of my unique IP row so I can have a start and finish time? I'M stuck. Would like to calculate the average time spent per IP. in a single row

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  • C++ Linked List - Reading data from a file with a sentinel

    - by Nick
    So I've done quite a bit of research on this and can't get my output to work correctly. I need to read in data from a file and have it stored into a Linked List. The while loop used should stop once it hits the $$$$$ sentinel. Then I am to display the data (by searching by ID Number[user input]) I am not that far yet I just want to properly display the data and get it read in for right now. My problem is when it displays the data is isn't stopping at the $$$$$ (even if I do "inFile.peek() != EOF and omit the $$$$$) I am still getting an extra garbage record. I know it has something to do with my while loop and how I am creating a new Node but I can't get it to work any other way. Any help would be appreciated. students.txt Nick J Cooley 324123 60 70 80 90 Jay M Hill 412254 70 80 90 100 $$$$$ assign6.h file #pragma once #include <iostream> #include <string> using namespace std; class assign6 { public: assign6(); // constructor void displayStudents(); private: struct Node { string firstName; string midIni; string lastName; int idNum; int sco1; //Test score 1 int sco2; //Test score 2 int sco3; //Test score 3 int sco4; //Test score 4 Node *next; }; Node *head; Node *headPtr; }; assign6Imp.cpp // Implementation File #include "assign6.h" #include <fstream> #include <iostream> #include <string> using namespace std; assign6::assign6() //constructor { ifstream inFile; inFile.open("students.txt"); head = NULL; head = new Node; headPtr = head; while (inFile.peek() != EOF) //reading in from file and storing in linked list { inFile >> head->firstName >> head->midIni >> head->lastName; inFile >> head->idNum; inFile >> head->sco1; inFile >> head->sco2; inFile >> head->sco3; inFile >> head->sco4; if (inFile != "$$$$$") { head->next = NULL; head->next = new Node; head = head->next; } } head->next = NULL; inFile.close(); } void assign6::displayStudents() { int average = 0; for (Node *cur = headPtr; cur != NULL; cur = cur->next) { cout << cur->firstName << " " << cur->midIni << " " << cur->lastName << endl; cout << cur->idNum << endl; average = (cur->sco1 + cur->sco2 + cur->sco3 + cur->sco4)/4; cout << cur->sco1 << " " << cur->sco2 << " " << cur->sco3 << " " << cur->sco4 << " " << "average: " << average << endl; } }

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  • Using XCode and instruments to improve iPhone app performance

    - by MrDatabase
    I've been experimenting with Instruments off and on for a while and and I still can't do the following (with any sensible results): determine or estimate the average runtime of a function that's called many times. For example if I'm driving my gameLoop at 60 Hz with a CADisplayLink I'd like to see how long the loop takes to run on average... 10 ms? 30 ms etc. I've come close with the "CPU activity" instrument but the results are inconsistent or don't make sense. The time profiler seems promising but all I can get is "% of runtime"... and I'd like an actual runtime.

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  • Ruby on Rails, PHP or C++ for web social network

    - by faya
    Hello, I have chosen diploma work in university. It's a mini social network. But now I am really stuck with which technology I should stick. I am average at C++ ISAPI web services development, below average PHP(had few projects with it) and new to Ruby and its framework RAILS. I have a deadline 1.5 month to develop it(about 5 hours every day after my full time job). Also I heard that its very easy to learn and develop with Ruby on Rails. Considering C++ I know that I have to do lots of coding and work by myself and PHP looks almost the same to me. So I am looking for you skilled developers advise what would you do in my position? Learn RoR, stick with C++ or PHP or maybe use something else?

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  • Python: Count lines and differentiate between them

    - by Mister X
    I'm using an application that gives a timed output based on how many times something is done in a minute, and I wish to manually take the output (copy paste) and have my program, and I wish to count how many times each minute it is done. An example output is this: 13:48 An event happened. 13:48 Another event happened. 13:49 A new event happened. 13:49 A random event happened. 13:49 An event happened. So, the program would need to understand that 2 things happened at 13:48, and 3 at 13:49. I'm not sure how the information would be stored, but I need to average them after, to determine an average of how often it happens. Sorry for being so complicated!

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  • Problem with acceding in DOM with jQuery

    - by Tristan
    Hello, I changed the tree of my JSON-P output, and i cannot access to my object DOM anymore : Here's my output : jsonp1271634374310( {"Inter-Medias": {"name":"Inter-Medias","idGSP":"14","average":"80","services":"8.86"} }); And here's my jQuery script : success: function(data, textStatus, XMLHttpRequest){ widget = data.name; widget += data.average ; .... I know one level is missing, but if I try to do : data.Inter-Medias.name or data.name.name it's still not working. Any idea please ? I will have case where i'll have multiple Ojbect, so i want to display all of them, how to do that ? for (i=0;i < data.length;i++) Does it look right ? Bonus question : i understand function(data, textStatus, XMLHttpRequest) that in case of success this function is triggered, the data is what the script recieved from his request, but i have no idea what textStatus or XMLHttpRequest are here too and why ?! Thank you.

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  • SQL Time(2) to Array in C#?

    - by Jacob Huggart
    Hello all, I am using ASP MVC and SQL Server and I have a database that is updated intermittently with expected wait times for some event. Also, I am using some ajax and jquery. I need to display the average and maximum wait times. How can I take the entire list of time from the server and get the average time? Also, what would be the best method to simply grab a new time from the server when it is updated without having to pull the whole list again? Thanks!

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  • Methodologies or algorithms for filling in missing data

    - by tbone
    I am dealing with datasets with missing data and need to be able to fill forward, backward, and gaps. So, for example, if I have data from Jan 1, 2000 to Dec 31, 2010, and some days are missing, when a user requests a timespan that begins before, ends after, or encompasses the missing data points, I need to "fill in" these missing values. Is there a proper term to refer to this concept of filling in data? Imputation is one term, don't know if it is "the" term for it though. I presume there are multiple algorithms & methodologies for filling in missing data (use last measured, using median/average/moving average, etc between 2 known numbers, etc. Anyone know the proper term for this problem, any online resources on this topic, or ideally links to open source implementations of some algorithms (C# preferably, but any language would be useful)

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  • need help with db-query on sql-server 2005.

    - by Avinash
    We're seeing strange behavior when running two versions of a query on SQL Server 2005: version A: SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = 1234 ORDER BY name ASC version B: DECLARE @Id AS INT; SET @Id = 1234; SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @Id ORDER BY name ASC Both queries return 1000 rows; version A takes on average 15s; version B on average takes 4s. Could anyone help us understand the difference in execution times of these two versions of SQL? If we invoke this query via named parameters using NHibernate, we see the following query via SQL Server profiler: EXEC sp_executesql N'SELECT otherattributes.* FROM listcontacts JOIN otherattributes ON listcontacts.contactId = otherattributes.contactId WHERE listcontacts.listid = @id ORDER BY name ASC', N'@id INT', @id=1234; ...and this tends to perform as badly as version A. Thanks in advance,

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  • JPQL: What kind of objects contains a result list when querying multiple columns?

    - by Bunkerbewohner
    Hello! I'm trying to do something which is easy as pie in PHP & Co: SELECT COUNT(x) as numItems, AVG(y) as average, ... FROM Z In PHP I would get a simple array like [{ numItems: 0, average: 0 }] which I could use like this: echo "Number of Items: " . $result[0]['numItems']; Usually in JPQL you only query single objects or single columns and get Lists types, for example List or List. But what do you get, when querying multiple columns?

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  • How to implement Voting for Grails Domain Classes?

    - by userWebMobile
    I have a Book class and need to implement a yes/no voting functionality. My domain classes look like this: class Book { String title static hasMany = [votes: Vote] } class User { String name static hasMany = [votes: Vote] } class Vote { boolean yesVote static belongsTo = [user: User, book: Book] } What is the best way to implement a voting for the book class. I need the following informations: What is the average yesVote for a book over all votes (either yes or no)? How to check if a specific user has done a vote? What is the best way to implement the computation of the average yesVote such that the performance does not drop?

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  • Problem with accessing in DOM with jQuery

    - by Tristan
    Hello, I changed the tree of my JSON-P output, and i cannot access to my object DOM anymore : Here's my output : jsonp1271634374310( {"Inter-Medias": {"name":"Inter-Medias","idGSP":"14","average":"80","services":"8.86"} }); And here's my jQuery script : success: function(data, textStatus, XMLHttpRequest){ widget = data.name; widget += data.average ; .... I know one level is missing, but if I try to do : data.Inter-Medias.name or data.name.name it's still not working. Any idea please ? I will have case where i'll have multiple Ojbect, so i want to display all of them, how to do that ? for (i=0;i < data.length;i++) Does it look right ? Bonus question : i understand function(data, textStatus, XMLHttpRequest) that in case of success this function is triggered, the data is what the script recieved from his request, but i have no idea what textStatus or XMLHttpRequest are here too and why ?! Thank you.

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  • Session Timeout and page response time

    - by Johnny5
    Hi, I'm load testing an asp.net app. The load test is simulating 500 user doing searchs on the site and browsing the results. I'm observing that the more I reduce the session timeout limit (in web.config) the better the page response time. For exemple, with a timeout at 10 minutes, I got an average response time of 8.35 seconds. With a timout at 3 minutes, the average response time for the same page is 3,98 seconds. The session in stored "InProc". I supposed the memory used by the "no more used but still actives" sessions may be in cause. But, even if there is more memory used when the timeout is at 10, there is still plenty of memory available (about 2.7Gb). Any ideas?

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  • Performance optimization for mssql: decrease stored procedures execution time or unload the server?

    - by tim
    Hello everybody! We have a web service which provides search over hotels. There is a problem with performance: a single request to the service takes around 5000 ms. Almost all of the time is spent in database by executing storing procedures. During the request our server (mssql2008) consumes ~90% of the processor time. When 2 requests are made in parallel the average time grows and is around 7000 ms. When number of request is increasing, the average time of response is increasing as well. We have 20-30 requests per minute. Which kind of optimization is the best in this case having in mind that the goal is to provide stable response time for the service: 1) Try to decrease the stored procedures execution time 2) Try to find the way how to unload the server It is interesting to hear from people who deal with booking sites. Thanks!

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  • TCP 30 small packets per second polutes connection with server

    - by Denis Ermolin
    I'm testing connection with flash client and cloud server(boost::asio for software) over TCP connection. My connection with server already is really poor - 120 ms ping in average. I found when i start to send packets with 2 bytes size (without tcp header) with speed 30 packets/s ping grow to 170-200 average. I think that it's really bad and my bad connection and bad cloud provider is reason for this high ping without any load. What do you think? (I tested my software and can compute about 50k packets/s so software is not a problem).

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  • template function error..

    - by sil3nt
    Hi there, I have function which takes in an parameter of a class called "Triple", and am returning the averge of 3 values of type float. template <typename ElemT> float average(Triple ElemT<float> &arg){ float pos1 = arg.getElem(1); float pos2 = arg.getElem(2); float pos3 = arg.getElem(3); return ( (pos1+pos2+po3) /3 ); } when i try compiling this i get q2b.cpp:32: error: template declaration of `float average' q2b.cpp:32: error: missing template arguments before "ElemT" not quite sure what this means.

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  • Proper Translation of equation to C#

    - by Shykin
    I am trying to replicate this equation: Slope(b) = (NSXY - (SX)(SY)) / (NSX2 - (SX)2) in C# but I'm getting the following issue: If I make the average of X = 1 + 2 + 3 + 4 + 5 and the average Y = 5 + 4 + 3 + 2 + 1 it gives me a positive slope even though it is clearly counting down. If I place the same numbers into this calculator: http://www.easycalculation.com/statistics/regression.php It gives me a negative slope in the linked calculator with the same data. I'm trying to narrow down the reasons so is the following a proper translation from equation to C# code: Slope(b) = (NSXY - (SX)(SY)) / (NSX2 - (SX)2) to Slope (m) = ((x * avgX * avgY) - (avgX * avgY)) / ((x * Math.Pow(avgX, 2)) - Math.Pow(avgX, 2));

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