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  • Which way to store this data is effective?

    - by Tattat
    I am writing a game, which need a map, and I want to store the map. The first thing I can think of, is using a 2D-array. But the problem is what data should I store in the 2D-array. The player can tap different place to have different reaction. So, I am thinking store a 2D-array with objects, when player click some position, and I find it in the array, and use the object in that array to execute a cmd. But I have a concern that storing lots of object may use lots of memory. So, I am think storing char/int only. But it seems that not enough for me. I want to store the data like that: { Type:1 Color:Green } No matter what color is, if they are all type 1, the have same reactions in logic, but the visual effect is based on the color. So, it is not easy to store using a prue char/int data, unless I make something like this: 1-5 --> all type 1. 1=color green , 2=color red, 3 = color yellow.... ... 6-10 --> all type 2. 2 = color green, 2 = color red ... ... So, do you have any ideas on how to minimize the ram use, but also easy for me to read... ...thx

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  • Using Custom Generic Collection faster with objects than List

    - by Kaminari
    I'm iterating through a List<> to find a matching element. The problem is that object has only 2 significant values, Name and Link (both strings), but has some other values which I don't want to compare. I'm thinking about using something like HashSet (which is exactly what I'm searching for -- fast) from .NET 3.5 but target framework has to be 2.0. There is something called Power Collections here: http://powercollections.codeplex.com/, should I use that? But maybe there is other way? If not, can you suggest me a suitable custom collection?

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  • MySQL, delete and index hint

    - by Manuel Darveau
    I have to delete about 10K rows from a table that has more than 100 million rows based on some criteria. When I execute the query, it takes about 5 minutes. I ran an explain plan (the delete query converted to select * since MySQL does not support explain delete) and found that MySQL uses the wrong index. My question is: is there any way to tell MySQL which index to use during delete? If not, what ca I do? Select to temp table then delete from temp table? Thank you!

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  • Fast find object by string property

    - by Andrew Kalashnikov
    Hello, colleagues. I've got task to fast find object by its string property. Object: class DicDomain { public virtual string Id{ get; set; } public virtual string Name { get; set; } } For storing my object I use List[T] dictionary where T is DicDomain for now . I've got 5-10 such lists, which contain about 500-20000 at each one. Task is find objects by its Name. I use next code now: List<T> entities = dictionary.FindAll(s => s.Name.Equals(word, StringComparison.OrdinalIgnoreCase)); I've got some questions: Is my search speed optimal. I think now. Data structure. It List good for this task. What about hashtable,sorted... Method Find. May be i should use string intern?? I haven't much exp at these tasks. Can u give me good advice for increase perfomance. Thanks

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  • Ternary Operators in JavaScript Without an "Else"

    - by Oscar Godson
    I've been using them forever, and I love them. To me they see cleaner and i can scan faster, but ever since I've been using them i've always had to put null in the else conditions that don't have anything. Is there anyway around it? E.g. condition ? x=true : null ; basically, is there a way to do: condition ? x=true; Now it shows up as a syntax error...

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  • optimize a string.Format + replace.

    - by acidzombie24
    I have this function. The visual studio profile marked the line with string.Format as hot and were i spend much of my time. How can i write this loop more efficiently? public string EscapeNoPredicate(string sz) { var s = new StringBuilder(sz); s.Replace(sepStr, sepStr + sepStr); foreach (char v in IllegalChars) { string s2 = string.Format("{0}{1:X2}", seperator, (Int16)v); s.Replace(v.ToString(), s2); } return s.ToString(); }

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  • Will an optimizing compiler remove calls to a method whose result will be multiplied by zero?

    - by Tim R.
    Suppose you have a computationally expensive method, Compute(p), which returns some float, and another method, Falloff(p), which returns another float from zero to one. If you compute Falloff(p) * Compute(p), will Compute(p) still run when Falloff(p) returns zero? Or would you need to write a special case to prevent Compute(p) from running unnecessarily? Theoretically, an optimizing compiler could determine that omitting Compute when Falloff returns zero would have no effect on the program. However, this is kind of hard to test, since if you have Compute output some debug data to determine whether it is running, the compiler would know not to omit it because of that debug info, resulting in sort of a Schrodinger's cat situation. I know the safe solution to this problem is just to add the special case, but I'm just curious.

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  • Word frequency tally script is too slow

    - by Dave Jarvis
    Background Created a script to count the frequency of words in a plain text file. The script performs the following steps: Count the frequency of words from a corpus. Retain each word in the corpus found in a dictionary. Create a comma-separated file of the frequencies. The script is at: http://pastebin.com/VAZdeKXs Problem The following lines continually cycle through the dictionary to match words: for i in $(awk '{if( $2 ) print $2}' frequency.txt); do grep -m 1 ^$i\$ dictionary.txt >> corpus-lexicon.txt; done It works, but it is slow because it is scanning the words it found to remove any that are not in the dictionary. The code performs this task by scanning the dictionary for every single word. (The -m 1 parameter stops the scan when the match is found.) Question How would you optimize the script so that the dictionary is not scanned from start to finish for every single word? The majority of the words will not be in the dictionary. Thank you!

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  • C++ pimpl idiom wastes an instruction vs. C style?

    - by Rob
    (Yes, I know that one machine instruction usually doesn't matter. I'm asking this question because I want to understand the pimpl idiom, and use it in the best possible way; and because sometimes I do care about one machine instruction.) In the sample code below, there are two classes, Thing and OtherThing. Users would include "thing.hh". Thing uses the pimpl idiom to hide it's implementation. OtherThing uses a C style – non-member functions that return and take pointers. This style produces slightly better machine code. I'm wondering: is there a way to use C++ style – ie, make the functions into member functions – and yet still save the machine instruction. I like this style because it doesn't pollute the namespace outside the class. Note: I'm only looking at calling member functions (in this case, calc). I'm not looking at object allocation. Below are the files, commands, and the machine code, on my Mac. thing.hh: class ThingImpl; class Thing { ThingImpl *impl; public: Thing(); int calc(); }; class OtherThing; OtherThing *make_other(); int calc(OtherThing *); thing.cc: #include "thing.hh" struct ThingImpl { int x; }; Thing::Thing() { impl = new ThingImpl; impl->x = 5; } int Thing::calc() { return impl->x + 1; } struct OtherThing { int x; }; OtherThing *make_other() { OtherThing *t = new OtherThing; t->x = 5; } int calc(OtherThing *t) { return t->x + 1; } main.cc (just to test the code actually works...) #include "thing.hh" #include <cstdio> int main() { Thing *t = new Thing; printf("calc: %d\n", t->calc()); OtherThing *t2 = make_other(); printf("calc: %d\n", calc(t2)); } Makefile: all: main thing.o : thing.cc thing.hh g++ -fomit-frame-pointer -O2 -c thing.cc main.o : main.cc thing.hh g++ -fomit-frame-pointer -O2 -c main.cc main: main.o thing.o g++ -O2 -o $@ $^ clean: rm *.o rm main Run make and then look at the machine code. On the mac I use otool -tv thing.o | c++filt. On linux I think it's objdump -d thing.o. Here is the relevant output: Thing::calc(): 0000000000000000 movq (%rdi),%rax 0000000000000003 movl (%rax),%eax 0000000000000005 incl %eax 0000000000000007 ret calc(OtherThing*): 0000000000000010 movl (%rdi),%eax 0000000000000012 incl %eax 0000000000000014 ret Notice the extra instruction because of the pointer indirection. The first function looks up two fields (impl, then x), while the second only needs to get x. What can be done?

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  • How to make this JavaScript much faster?

    - by Ralph
    Still trying to answer this question, and I think I finally found a solution, but it runs too slow. var $div = $('<div>') .css({ 'border': '1px solid red', 'position': 'absolute', 'z-index': '65535' }) .appendTo('body'); $('body *').live('mousemove', function(e) { var topElement = null; $('body *').each(function() { if(this == $div[0]) return true; var $elem = $(this); var pos = $elem.offset(); var width = $elem.width(); var height = $elem.height(); if(e.pageX > pos.left && e.pageY > pos.top && e.pageX < (pos.left + width) && e.pageY < (pos.top + height)) { var zIndex = document.defaultView.getComputedStyle(this, null).getPropertyValue('z-index'); if(zIndex == 'auto') zIndex = $elem.parents().length; if(topElement == null || zIndex > topElement.zIndex) { topElement = { 'node': $elem, 'zIndex': zIndex }; } } }); if(topElement != null ) { var $elem = topElement.node; $div.offset($elem.offset()).width($elem.width()).height($elem.height()); } }); It basically loops through all the elements on the page and finds the top-most element beneath the cursor. Is there maybe some way I could use a quad-tree or something and segment the page so the loop runs faster?

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  • MySQL Datefields: duplicate or calculate?

    - by Konerak
    We are using a table with a structure imposed upon us more than 10 years ago. We are allowed to add columns, but urged not to change existing columns. Certain columns are meant to represent dates, but are put in different format. Amongst others: * CHAR(6): YYMMDD * CHAR(6): DDMMYY * CHAR(8): YYYYMMDD * CHAR(8): DDMMYYYY * DATE * DATETIME Since we now would like to do some more complex queries, using advanced date functions, my manager proposed to d*uplicate those problem columns* to a proper FORMATTED_OLDCOLUMNNAME column using a DATE or DATETIME format. Is this the way to go? Couldn't we just use the STR_TO_DATE function each time we accessed the columns? To avoid every query having to copy-paste the function, I could still work with a view or a stored procedure, but duplicating data to avoid recalculation sounds wrong. Solutions I see (I guess I prefer 2.2.1) 1. Physically duplicate columns 1.1 In the same table 1.1.1 Added by each script that does a modification (INSERT/UPDATE/REPLACE/...) 1.1.2 Maintained by a trigger on each modification 1.2 In a separate table 1.2.1 Added by each script that does a modification (INSERT/UPDATE/REPLACE/...) 1.2.2 Maintained by a trigger on each modification 2. On-demand transformation 2.1 Each query has to perform the transformation 2.1.1 Using copy-paste in the source code 2.1.2 Using a library 2.1.3 Using a STORED PROCEDURE 2.2 A view performs the transformation 2.2.1 A separate table replacing the entire table 2.2.2 A separate table just adding the date-fields for the primary keys Am I right to say it's better to recalculate than to store? And would a view be a good solution?

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  • Optimizing sparse dot-product in C#

    - by Haggai
    Hello. I'm trying to calculate the dot-product of two very sparse associative arrays. The arrays contain an ID and a value, so the calculation should be done only on those IDs that are common to both arrays, e.g. <(1, 0.5), (3, 0.7), (12, 1.3) * <(2, 0.4), (3, 2.3), (12, 4.7) = 0.7*2.3 + 1.3*4.7 . My implementation (call it dict) currently uses Dictionaries, but it is too slow to my taste. double dot_product(IDictionary<int, double> arr1, IDictionary<int, double> arr2) { double res = 0; double val2; foreach (KeyValuePair<int, double> p in arr1) if (arr2.TryGetValue(p.Key, out val2)) res += p.Value * val2; return res; } The full arrays have about 500,000 entries each, while the sparse ones are only tens to hundreds entries each. I did some experiments with toy versions of dot products. First I tried to multiply just two double arrays to see the ultimate speed I can get (let's call this "flat"). Then I tried to change the implementation of the associative array multiplication using an int[] ID array and a double[] values array, walking together on both ID arrays and multiplying when they are equal (let's call this "double"). I then tried to run all three versions with debug or release, with F5 or Ctrl-F5. The results are as follows: debug F5: dict: 5.29s double: 4.18s (79% of dict) flat: 0.99s (19% of dict, 24% of double) debug ^F5: dict: 5.23s double: 4.19s (80% of dict) flat: 0.98s (19% of dict, 23% of double) release F5: dict: 5.29s double: 3.08s (58% of dict) flat: 0.81s (15% of dict, 26% of double) release ^F5: dict: 4.62s double: 1.22s (26% of dict) flat: 0.29s ( 6% of dict, 24% of double) I don't understand these results. Why isn't the dictionary version optimized in release F5 as do the double and flat versions? Why is it only slightly optimized in the release ^F5 version while the other two are heavily optimized? Also, since converting my code into the "double" scheme would mean lots of work - do you have any suggestions how to optimize the dictionary one? Thanks! Haggai

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  • How do I select a random record efficiently in MySQL?

    - by user198729
    mysql> EXPLAIN SELECT * FROM urls ORDER BY RAND() LIMIT 1; +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ | 1 | SIMPLE | urls | ALL | NULL | NULL | NULL | NULL | 62228 | Using temporary; Using filesort | +----+-------------+-------+------+---------------+------+---------+------+-------+---------------------------------+ The above doesn't qualify as efficient,how should I do it properly?

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  • File IO with Streams - Best Memory Buffer Size

    - by AJ
    I am writing a small IO library to assist with a larger (hobby) project. A part of this library performs various functions on a file, which is read / written via the FileStream object. On each StreamReader.Read(...) pass, I fire off an event which will be used in the main app to display progress information. The processing that goes on in the loop is vaired, but is not too time consuming (it could just be a simple file copy, for example, or may involve encryption...). My main question is: What is the best memory buffer size to use? Thinking about physical disk layouts, I could pick 2k, which would cover a CD sector size and is a nice multiple of a 512 byte hard disk sector. Higher up the abstraction tree, you could go for a larger buffer which could read an entire FAT cluster at a time. I realise with today's PC's, I could go for a more memory hungry option (a couple of MiB, for example), but then I increase the time between UI updates and the user perceives a less responsive app. As an aside, I'm eventually hoping to provide a similar interface to files hosted on FTP / HTTP servers (over a local network / fastish DSL). What would be the best memory buffer size for those (again, a "best-case" tradeoff between perceived responsiveness vs. performance).

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  • SQL Database dilemma : Optimize for Querying or Writing?

    - by Harry
    I'm working on a personal project (Search engine) and have a bit of a dilemma. At the moment it is optimized for writing data to the search index and significantly slow for search queries. The DTA (Database Engine Tuning Adviser) recommends adding a couple of Indexed views inorder to speed up search queries. But this is to the detriment of writing new data to the DB. It seems I can't have one without the other! This is obviously not a new problem. What is a good strategy for this issue?

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  • Efficiently draw a grid in Windows Forms

    - by Joel
    I'm writing an implementation of Conway's Game of Life in C#. This is the code I'm using to draw the grid, it's in my panel_Paint event. g is the graphics context. for (int y = 0; y < numOfCells * cellSize; y += cellSize) { for (int x = 0; x < numOfCells * cellSize; x += cellSize) { g.DrawLine(p, x, 0, x, y + numOfCells * cellSize); g.DrawLine(p, 0, x, y + size * drawnGrid, x); } } When I run my program, it is unresponsive until it finishes drawing the grid, which takes a few seconds at numOfCells = 100 & cellSize = 10. Removing all the multiplication makes it faster, but not by very much. Is there a better/more efficient way to draw my grid? Thanks

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  • Does the compiler optimize the function parameters passed by value?

    - by Naveen
    Lets say I have a function where the parameter is passed by value instead of const-reference. Further, lets assume that only the value is used inside the function i.e. the function doesn't try to modify it. In that case will the compiler will be able to figure out that it can pass the value by const-reference (for performance reasons) and generate the code accordingly? Is there any compiler which does that?

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  • Why isn't the copy constructor elided here?

    - by Jesse Beder
    (I'm using gcc with -O2.) This seems like a straightforward opportunity to elide the copy constructor, since there are no side-effects to accessing the value of a field in a bar's copy of a foo; but the copy constructor is called, since I get the output meep meep!. #include <iostream> struct foo { foo(): a(5) { } foo(const foo& f): a(f.a) { std::cout << "meep meep!\n"; } int a; }; struct bar { foo F() const { return f; } foo f; }; int main() { bar b; int a = b.F().a; return 0; }

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  • Specific template for the first element.

    - by Kalinin
    I have a template: <xsl:template match="paragraph"> ... </xsl:template> I call it: <xsl:apply-templates select="paragraph"/> For the first element I need to do: <xsl:template match="paragraph[1]"> ... <xsl:apply-templates select="."/><!-- I understand that this does not work --> ... </xsl:template> How to call <xsl:apply-templates select="paragraph"/> (for the first element paragraph) from the template <xsl:template match="paragraph[1]">? So far that I have something like a loop. I solve this problem so (but I do not like it): <xsl:for-each select="paragraph"> <xsl:choose> <xsl:when test="position() = 1"> ... <xsl:apply-templates select="."/> ... </xsl:when> <xsl:otherwise> <xsl:apply-templates select="."/> </xsl:otherwise> </xsl:choose> </xsl:for-each>

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  • Optimize INSERT / UPDATE / DELETE operation

    - by clime
    I wonder if the following script can be optimized somehow. It does write a lot to disk because it deletes possibly up-to-date rows and reinserts them. I was thinking about applying something like "insert ... on duplicate key update" and found some possibilities for single-row updates but I don't know how to apply it in the context of INSERT INTO ... SELECT query. CREATE OR REPLACE FUNCTION update_member_search_index() RETURNS VOID AS $$ DECLARE member_content_type_id INTEGER; BEGIN member_content_type_id := (SELECT id FROM django_content_type WHERE app_label='web' AND model='member'); DELETE FROM watson_searchentry WHERE content_type_id = member_content_type_id; INSERT INTO watson_searchentry (engine_slug, content_type_id, object_id, object_id_int, title, description, content, url, meta_encoded) SELECT 'default', member_content_type_id, web_member.id, web_member.id, web_member.name, '', web_user.email||' '||web_member.normalized_name||' '||web_country.name, '', '{}' FROM web_member INNER JOIN web_user ON (web_member.user_id = web_user.id) INNER JOIN web_country ON (web_member.country_id = web_country.id) WHERE web_user.is_active=TRUE; END; $$ LANGUAGE plpgsql; EDIT: Schemas of web_member, watson_searchentry, web_user, web_country: http://pastebin.com/3tRVPPVi. (content_type_id, object_id_int) in watson_searchentry is unique pair in the table but atm the index is not present (there is no use for it). This script should be run at most once a day for full rebuilds of search index.

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  • Has anyone ever successfully make index merge work for MySQL?

    - by user198729
    Setup: mysql> create table t(a integer unsigned,b integer unsigned); mysql> insert into t(a,b) values (1,2),(1,3),(2,4); mysql> create index i_t_a on t(a); mysql> create index i_t_b on t(b); mysql> explain select * from t where a=1 or b=4; +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | t | ALL | i_t_a,i_t_b | NULL | NULL | NULL | 3 | Using where | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ Is there something I'm missing? Update mysql> explain select * from t where a=1 or b=4; +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ | 1 | SIMPLE | t | ALL | i_t_a,i_t_b | NULL | NULL | NULL | 1863 | Using where | +----+-------------+-------+------+---------------+------+---------+------+------+-------------+ Version: mysql> select version(); +----------------------+ | version() | +----------------------+ | 5.1.36-community-log | +----------------------+ Has anyone ever successfully make index merge work for MySQL? I'll be glad to see successful stories here:)

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  • Get count matches in query on large table very slow

    - by Roy Roes
    I have a mysql table "items" with 2 integer fields: seid and tiid The table has about 35000000 records, so it's very large. seid tiid ----------- 1 1 2 2 2 3 2 4 3 4 4 1 4 2 The table has a primary key on both fields, an index on seid and an index on tiid. Someone types in 1 or more tiid values and now I would like to get the seid with most results. For example when someone types 1,2,3, I would like to get seid 2 and 4 as result. They both have 2 matches on the tiid values. My query so far: SELECT COUNT(*) as c, seid FROM items WHERE tiid IN (1,2,3) GROUP BY seid HAVING c = (SELECT COUNT(*) as c, seid FROM items WHERE tiid IN (1,2,3) GROUP BY seid ORDER BY c DESC LIMIT 1) But this query is extremly slow, because of the large table. Does anyone know how to construct a better query for this purpose?

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