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  • Efficient Array Storage for Binary Tree

    - by Sundararajan S
    We have to write the nodes of a binary tree to a file. What is the most space efficient way of writing a binary tree . We can store it in array format with parent in position 'i' and its childs in 2i,2i+1. But this will waste lot of space in case of sparse binary trees.

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  • More efficient left join of big table

    - by Zeus
    Hello, I have the following (simplified) query select P.peopleID, P.peopleName, ED.DataNumber from peopleTable P left outer join ( select PE.peopleID, PE.DataNumber from formElements FE inner join peopleExtra PE on PE.ElementID = FE.FormElementID where FE.FormComponentID = 42 ) ED on ED.peopleID = P.peopleID Without the sub-query this procedure takes ~7 seconds, but with it, it takes about 3minutes. Given that table peopleExtra is rather large, is there a more efficient way to do that join (short of restructuring the DB) ?

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  • Efficient way in Python to remove an element from a comma-separated string

    - by ensnare
    I'm looking for the most efficient way to add an element to a comma-separated string while maintaining alphabetical order for the words: For example: string = 'Apples, Bananas, Grapes, Oranges' subtraction = 'Bananas' result = 'Apples, Grapes, Oranges' Also, a way to do this but while maintaining IDs: string = '1:Apples, 4:Bananas, 6:Grapes, 23:Oranges' subtraction = '4:Bananas' result = '1:Apples, 6:Grapes, 23:Oranges' Sample code is greatly appreciated. Thank you so much.

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  • WPF on a iX104 Tablet PC - efficient enough?

    - by Casimodo72
    Hi, I'm considering to use WPF for an application running on an iX104 (unfortunately I don't have one of those yet). Do you guys think that this combination would be efficient enough? Or is WPF just to slow for such a machine, so better stick with WinForms? Relevant specs of the iX104: Intel Pentium U2500 CoreDuo 2x 1.2 GHz 1 GB RAM, optional 2 GB 10.4" TFT, XGA 1024x768 Regards, Kasimier

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  • Efficient SQL to count an occurrence in the latest X rows

    - by pulegium
    For example I have: create table a (i int); Assume there are 10k rows. I want to count 0's in the last 20 rows. Something like: select count(*) from (select i from a limit 20) where i = 0; Is that possible to make it more efficient? Like a single SQL statement or something? PS. DB is SQLite3 if that matters at all...

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  • C/C++ efficient bit array

    - by aaa
    hi. Can you recommend efficient/clean way to manipulate arbitrary length bit array? right now I am using regular int/char bitmask, but those are not very clean when array length is greater than datatype length. std vector<bool> is not available for me. thanks

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  • Efficient way to store a graph for calculation in Hadoop

    - by user337499
    I am currently trying to perform calculations like clustering coefficient on huge graphs with the help of Hadoop. Therefore I need an efficient way to store the graph in a way that I can easily access nodes, their neighbors and the neighbors' neighbors. The graph is quite sparse and stored in a huge tab separated file where the first field is the node from which an edge goes to the second node in field two. Thanks in advance!

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  • Which of these queries is more efficient?

    - by Brian
    Which of these queries are more efficient? select 1 as newAndClosed from sysibm.sysdummy1 where exists ( select 1 from items where new = 1 ) and not exists ( select 1 from status where open = 1 ) select 1 as newAndClosed from items where new = 1 and not exists ( select 1 from status where open = 1 )

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  • Efficient 4x4 matrix inverse (affine transform)

    - by Budric
    Hi, I was hoping someone can point out an efficient formula for 4x4 affine matrix transform. Currently my code uses cofactor expansion and it allocates a temporary array for each cofactor. It's easy to read, but it's slower than it should be. Note, this isn't homework and I know how to work it out manually using 4x4 co-factor expansion, it's just a pain and not really an interesting problem for me. Also I've googled and came up with a few sites that give you the formula already (http://www.euclideanspace.com/maths/algebra/matrix/functions/inverse/fourD/index.htm). However this one could probably be optimized further by pre-computing some of the products. I'm sure someone came up with the "best" formula for this at one point or another? Thanks.

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  • What is an efficient way to write password cracking algorithm (python)

    - by Luminance
    This problem might be relatively simple, but I'm given two text files. One text file contains all encrypted passwords encrypted via crypt.crypt in python. The other list contains over 400k+ normal dictionary words. The assignment is that given 3 different functions which transform strings from their normal case to all different permutations of capitalizations, transforms a letter to a number (if it looks alike, e.g. G - 6, B - 8), and reverses a string. The thing is that given the 10 - 20 encrypted passwords in the password file, what is the most efficient way to get the fastest running solution in python to run those functions on dictionary word in the words file? It is given that all those words, when transformed in whatever way, will encrypt to a password in the password file. Here is the function which checks if a given string, when encrypted, is the same as the encrypted password passed in: def check_pass(plaintext,encrypted): crypted_pass = crypt.crypt(plaintext,encrypted) if crypted_pass == encrypted: return True else: return False Thanks in advance.

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  • Efficient counting of an association’s association

    - by Matthew Robertson
    In my app, when a User makes a Comment in a Post, Notifications are generated that marks that comment as unread. class Notification < ActiveRecord::Base belongs_to :user belongs_to :post belongs_to :comment class User < ActiveRecord::Base has_many :notifications class Post < ActiveRecord::Base has_many :notifications I’m making an index page that lists all the posts for a user and the notification count for each post for just that user. # posts controller @posts = Post.where( :user_id => current_user.id ) .includes(:notifications) # posts view @posts.each do |post| <%= post.notifications.count %> This doesn’t work because it counts notifications for all users. What’s an efficient way to do this without running a separate query for each post?

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  • Efficient Search function with Linq to SQL

    - by Bayonian
    Hi, I'm using VB.NET and Linq to SQL. I have a table with thousands of rows and growing. Right now I'm using .Contains() in the Where clause to perform the query. Below is my search function : Public Shared Function DemoSearchFunction(ByVal keyword As String) As DataTable Dim db As New BibleDataClassesDataContext() Dim query = From b In db.khmer_books _ From ch In db.khmer_chapters _ From v In db.testing_khmers _ Where v.t_v.Contains(keyword) And ch.kh_book_id = b.kh_b_id And v.t_chid = ch.kh_ch_id _ Select b.kh_b_id, b.kh_b_title, ch.kh_ch_id, ch.kh_ch_number, v.t_id, v.t_vn, v.t_v Dim dtDataTableOne = New DataTable("dtOne") dtDataTableOne.Columns.Add("bid", GetType(Integer)) dtDataTableOne.Columns.Add("btitle", GetType(String)) dtDataTableOne.Columns.Add("chid", GetType(Integer)) dtDataTableOne.Columns.Add("chn", GetType(Integer)) dtDataTableOne.Columns.Add("vid", GetType(Integer)) dtDataTableOne.Columns.Add("vn", GetType(Integer)) dtDataTableOne.Columns.Add("verse", GetType(String)) For Each r In query dtDataTableOne.Rows.Add(New Object() {r.kh_b_id, r.kh_b_title, r.kh_ch_id, r.kh_ch_number, r.t_id, r.t_vn, r.t_v}) Next Return dtDataTableOne End Function I would like to know other methods for doing efficient search using Linq to SQL. Thanks.

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  • Memory efficient import many data files into panda DataFrame in Python

    - by richardh
    I import into a panda DataFrame a directory of |-delimited.dat files. The following code works, but I eventually run out of RAM with a MemoryError:. import pandas as pd import glob temp = [] dataDir = 'C:/users/richard/research/data/edgar/masterfiles' for dataFile in glob.glob(dataDir + '/master_*.dat'): print dataFile temp.append(pd.read_table(dataFile, delimiter='|', header=0)) masterAll = pd.concat(temp) Is there a more memory efficient approach? Or should I go whole hog to a database? (I will move to a database eventually, but I am baby stepping my move to pandas.) Thanks! FWIW, here is the head of an example .dat file: cik|cname|ftype|date|fileloc 1000032|BINCH JAMES G|4|2011-03-08|edgar/data/1000032/0001181431-11-016512.txt 1000045|NICHOLAS FINANCIAL INC|10-Q|2011-02-11|edgar/data/1000045/0001193125-11-031933.txt 1000045|NICHOLAS FINANCIAL INC|8-K|2011-01-11|edgar/data/1000045/0001193125-11-005531.txt 1000045|NICHOLAS FINANCIAL INC|8-K|2011-01-27|edgar/data/1000045/0001193125-11-015631.txt 1000045|NICHOLAS FINANCIAL INC|SC 13G/A|2011-02-14|edgar/data/1000045/0000929638-11-00151.txt

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  • Do you know a good and efficient FFT?

    - by yan bellavance
    Hi, I am trying to find a very fast and efficient Fourier transform (FFT). Does anyone know of any good ones. I need to run it on the iPhone so it must not be intensive. Instead, maybe you know of one that is wavelet like, i need frequency resolution but only a narrow band (vocal audio range up to 10khz max...even 10Khz might be too high). Im thinking also of truncating this FFT to keep the frequency resolution while eliminating the unwanted frequency band. This is for an iphone ...I have taken a look at the FFT in Aurio touch but it seems this is an int FFT but my app uses floats.....would it give a big performance increase to try and adapt program to an int FFT or not(which i really dont feel like doing...plus aurio touch uses a radix 2 FFT which is not that great).

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  • Please for efficient query

    - by user278618
    I want to have efficient query to get some rows from my table. Here is I think the best presentation of my table. -Somedate is not duplicated - it is date of modifiedon -a,b,c are parent ids, let say countryCode -1,2,3,4 are subparent, let say citycode -guids are id of rows -true, false are values of rows - one can name this column - freshAir a 1 GUID somedate true a 1 GUID somedate true a 2 GUID somedate false a 2 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 3 GUID somedate false b 4 GUID somedate false c 5 GUID somedate true c 6 GUID somedate true c 6 GUID somedate false c 6 GUID somedate false c 7 GUID somedate false I want the most recent rows MAX(modifiedon) grouped by countrycode and citycode and in this groups I need elements which have another values (true, false). And in result I want: a 1 GUID somedate true a 2 GUID somedate false c 5 GUID somedate true c 6 GUID somedate false c 7 GUID somedate false Look that in result I don't want to have records with "b", because all rows have the same value (false). Best regards

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  • Efficient JSON encoding for data that may be binary, but is often text

    - by Evgeny
    I need to send a JSON packet across the wire with the contents of an arbitrary file. This may be a binary file (like a ZIP file), but most often it will be plain ASCII text. I'm currently using base64 encoding, which handles all files, but it increases the size of the data significantly - even if the file is ASCII to begin with. Is there a more efficient way I can encode the data, other than manually checking for any non-ASCII characters and then deciding whether or not to base64-encode it? I'm currently writing this in Python, but will probably need to do the same in Java, C# and C++, so an easily portable solution would be preferable.

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  • Struct in C, are they efficient?

    - by pygabriel
    I'm reading some C code like that: double function( int lena,double xa,double ya, double za, double *acoefs, ..., int lenb,double xb,double yb, double zb, double *bcoefs, ..., same for c, same for d ) This function is called in the code mor than 100.000 times so it's performance-critical. I'm trying to extend this code but I want to know if it's efficient or not (and how much this influences the speed) to encapsulate all the parameters in a struct like this struct PGTO { int len; double x,y,z ; double *acoefs } and then access the parameters in the function.

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  • Efficient heaps in purely functional languages

    - by Kim
    As an exercise in Haskell, I'm trying to implement heapsort. The heap is usually implemented as an array in imperative languages, but this would be hugely inefficient in purely functional languages. So I've looked at binary heaps, but everything I found so far describes them from an imperative viewpoint and the algorithms presented are hard to translate to a functional setting. How to efficiently implement a heap in a purely functional language such as Haskell? Edit: By efficient I mean it should still be in O(n*log n), but it doesn't have to beat a C program. Also, I'd like to use purely functional programming. What else would be the point of doing it in Haskell?

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  • Most efficient way to create and nest divs with appendChild using *plain* javascript (no libraries)

    - by Matrym
    Is there a more efficient way to write the following appendChild / nesting code? var sasDom, sasDomHider; var d = document; var docBody = d.getElementsByTagName("body")[0]; var newNode = d.createElement('span'); var secondNode = d.createElement('span'); // Hider dom newNode.setAttribute("id", "sasHider"); docBody.appendChild(newNode); sasDomHider = d.getElementById("sasHider"); // Copyier dom secondNode.setAttribute("id", "sasText"); sasDomHider.appendChild(secondNode); sasDom = d.getElementById("sasText"); Thanks in advance for your time :)

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