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  • Use a vector to index a matrix without linear index

    - by David_G
    G'day, I'm trying to find a way to use a vector of [x,y] points to index from a large matrix in MATLAB. Usually, I would convert the subscript points to the linear index of the matrix.(for eg. Use a vector as an index to a matrix in MATLab) However, the matrix is 4-dimensional, and I want to take all of the elements of the 3rd and 4th dimensions that have the same 1st and 2nd dimension. Let me hopefully demonstrate with an example: Matrix = nan(4,4,2,2); % where the dimensions are (x,y,depth,time) Matrix(1,2,:,:) = 999; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(3,4,:,:) = 888; % note that this value could change in depth (3rd dim) and time (4th time) Matrix(4,4,:,:) = 124; Now, I want to be able to index with the subscripts (1,2) and (3,4), etc and return not only the 999 and 888 which exist in Matrix(:,:,1,1) but the contents which exist at Matrix(:,:,1,2),Matrix(:,:,2,1) and Matrix(:,:,2,2), and so on (IRL, the dimensions of Matrix might be more like size(Matrix) = (300 250 30 200) I don't want to use linear indices because I would like the results to be in a similar vector fashion. For example, I would like a result which is something like: ans(time=1) 999 888 124 999 888 124 ans(time=2) etc etc etc etc etc etc I'd also like to add that due to the size of the matrix I'm dealing with, speed is an issue here - thus why I'd like to use subscript indices to index to the data. I should also mention that (unlike this question: Accessing values using subscripts without using sub2ind) since I want all the information stored in the extra dimensions, 3 and 4, of the i and jth indices, I don't think that a slightly faster version of sub2ind still would not cut it..

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  • What are some best practises and "rules of thumb" for creating database indexes?

    - by Ash
    I have an app, which cycles through a huge number of records in a database table and performs a number of SQL and .Net operations on records within that database (currently I am using Castle.ActiveRecord on PostgreSQL). I added some basic btree indexes on a couple of the feilds, and as you would expect, the peformance of the SQL operations increased substantially. Wanting to make the most of dbms performance I want to make some better educated choices about what I should index on all my projects. I understand that there is a detrement to performance when doing inserts (as the database needs to update the index, as well as the data), but what suggestions and best practices should I consider with creating database indexes? How do I best select the feilds/combination of fields for a set of database indexes (rules of thumb)? Also, how do I best select which index to use as a clustered index? And when it comes to the access method, under what conditions should I use a btree over a hash or a gist or a gin (what are they anyway?).

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  • javascript increment index in funciton

    - by mcgrailm
    I'm just trying to figure out how to create an index inside a function so I can keep track of the items its generating and I'm not sure how to do this seems like I should know this.. addLocation(options,location) funciton addLocation(options,location){ $('#list').append('<li class="location"><div>'+location.label+'</div>'+ '<input type="hidden" name="location['+x+'][lat]" value="'+location.lat+'" />'+ '<input type="hidden" name="location['+x+'][lon]" value="'+location.lon+'" />'+ '<input type="hidden" name="location['+x+'][loc]" value="'+location.loc+'" />'+ '<input type="hidden" name="location['+x+'][label]" value="'+location.label+'" />'+ '</li>'); } now normally you have a forloop to help you keep track of things but int this instance I'm not appending items in a loop and I keep getting an error saying x in undefined appreciate any help you can give thanks Mike

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  • Please help optimizing a long running query (left outer join, with 2 subqueries)

    - by 46and2
    Hi all. The query I need help with is: SELECT d.bn, d.4700, d.4500, ... , p.`Activity Description` FROM ( SELECT temp.bn, temp.4700, temp.4500, .... FROM `tdata` temp GROUP BY temp.bn HAVING (COUNT(temp.bn) = 1) ) d LEFT OUTER JOIN ( SELECT temp2.bn, max(temp2.FPE) AS max_fpe, temp2.`Activity Description` FROM `pdata` temp2 GROUP BY temp2.bn ) p ON p.bn = d.bn; The ... represents other fields that aren't really important to solving this problem. The issue is on the the second subquery - it is not using the index I have created and I am not sure why, it seems to be because of the way TEXT fields are handled. The first subquery uses the index I have created and runs quite snappy, however an explain on the second shows a 'Using temporary; Using filesort'. Please see the indexes I have created in the below table create statements. Can anyone help me optimize this? By way of quick explanation the first subquery is meant to only select records that have unique bn's, the second, while it looks a bit wacky (with the max function there which is not being used in the result set) is making sure that only one record from the right part of the join is included in the result set. My table create statements are CREATE TABLE `tdata` ( `BN` varchar(15) DEFAULT NULL, `4000` varchar(3) DEFAULT NULL, `5800` varchar(3) DEFAULT NULL, .... KEY `BN` (`BN`), KEY `idx_t3010`(`BN`,`4700`,`4500`,`4510`,`4520`,`4530`,`4570`,`4950`,`5000`,`5010`,`5020`,`5050`,`5060`,`5070`,`5100`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 CREATE TABLE `pdata` ( `BN` varchar(15) DEFAULT NULL, `FPE` datetime DEFAULT NULL, `Activity Description` text, .... KEY `BN` (`BN`), KEY `idx_programs_2009` (`BN`,`FPE`,`Activity Description`(100)) ) ENGINE=MyISAM DEFAULT CHARSET=utf8 Thanks!

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  • Help on understanding multiple columns on an index?

    - by Xaisoft
    Assume I have a table called "table" and I have 3 columns, a, b, and c. What does it mean to have a non-clustered index on columns a,b? Is a nonclustered index on columns a,b the same as a nonclustered index on columns b,a? (Note the order). Also, Is a nonclustered index on column a the same as a nonclustered index on a,c? I was looking at the website sqlserver performance and they had these dmv scripts where it would tell you if you had overlapping indexes and I believe it was saying that having an index on a is the same as a,b, so it is redundant. Is this true about indexes? One last question is why is the clustered index put on the primary key. Most of the time the primary key is not queried against, so shouldn't the clustered index be on the most queried column. I am probably missing something here like having it on the primary key speeds up joins? Great explanations. Should I turn this into a wiki and change the title index explanation?

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  • How do you efficiently bulk index lookups?

    - by Liron Shapira
    I have these entity kinds: Molecule Atom MoleculeAtom Given a list(molecule_ids) whose lengths is in the hundreds, I need to get a dict of the form {molecule_id: list(atom_ids)}. Likewise, given a list(atom_ids) whose length is in the hunreds, I need to get a dict of the form {atom_id: list(molecule_ids)}. Both of these bulk lookups need to happen really fast. Right now I'm doing something like: atom_ids_by_molecule_id = {} for molecule_id in molecule_ids: moleculeatoms = MoleculeAtom.all().filter('molecule =', db.Key.from_path('molecule', molecule_id)).fetch(1000) atom_ids_by_molecule_id[molecule_id] = [ MoleculeAtom.atom.get_value_for_datastore(ma).id() for ma in moleculeatoms ] Like I said, len(molecule_ids) is in the hundreds. I need to do this kind of bulk index lookup on almost every single request, and I need it to be FAST, and right now it's too slow. Ideas: Will using a Molecule.atoms ListProperty do what I need? Consider that I am storing additional data on the MoleculeAtom node, and remember it's equally important for me to do the lookup in the molecule-atom and atom-molecule directions. Caching? I tried memcaching lists of atom IDs keyed by molecule ID, but I have tons of atoms and molecules, and the cache can't fit it. How about denormalizing the data by creating a new entity kind whose key name is a molecule ID and whose value is a list of atom IDs? The idea is, calling db.get on 500 keys is probably faster than looping through 500 fetches with filters, right?

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  • Caching linked pages in ASP.NET

    - by n0e
    I'm thinking of a way of creating a local backup for the pages I will be linking to from my site. This would be text-only, similar to Google's 'Copy' feature on the search pages. The idea is to be sure that the pages I would reference to, or cite from, do not dissapear from the Web in the near future. I know I could just keep local copies, but I will have A LOT of citations. What would be the best way of achieving this in ASP.NET? Some custom caching in database?

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  • SQLAlchemy custom sorting algorithms when using SQL indexes

    - by David M
    Is it possible to write custom collation functions with indexes in SQLAlchemy? SQLite for example allows specifying the sorting function at a C level as sqlite3_create_collation(). An implementation of some of the Unicode collation algorithm has been provided by James Tauber here, which for example sorts all the "a"'s close together whether they have accents on them or not. Other examples of why this might be useful is for different alphabet orders (languages other than English) and sorting numeric values (sorting 10 after 9 rather than codepoint order.) Is this possible in SQLAlchemy? If not, is it supported by the pysqlite3 or MySQLdb modules, or for any other SQL database modules supported by python for that matter? Any information would be greatly appreciated.

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  • How to optimize this SQL query for a rectangular region?

    - by Andrew B.
    I'm trying to optimize the following query, but it's not clear to me what index or indexes would be best. I'm storing tiles in a two-dimensional plane and querying for rectangular regions of that plane. The table has, for the purposes of this question, the following columns: id: a primary key integer world_id: an integer foreign key which acts as a namespace for a subset of tiles tileY: the Y-coordinate integer tileX: the X-coordinate integer value: the contents of this tile, a varchar if it matters. I have the following indexes: "ywot_tile_pkey" PRIMARY KEY, btree (id) "ywot_tile_world_id_key" UNIQUE, btree (world_id, "tileY", "tileX") "ywot_tile_world_id" btree (world_id) And this is the query I'm trying to optimize: ywot=> EXPLAIN ANALYZE SELECT * FROM "ywot_tile" WHERE ("world_id" = 27685 AND "tileY" <= 6 AND "tileX" <= 9 AND "tileX" >= -2 AND "tileY" >= -1 ); QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------- Bitmap Heap Scan on ywot_tile (cost=11384.13..149421.27 rows=65989 width=168) (actual time=79.646..80.075 rows=96 loops=1) Recheck Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) -> Bitmap Index Scan on ywot_tile_world_id_key (cost=0.00..11367.63 rows=65989 width=0) (actual time=79.615..79.615 rows=125 loops=1) Index Cond: ((world_id = 27685) AND ("tileY" <= 6) AND ("tileY" >= (-1)) AND ("tileX" <= 9) AND ("tileX" >= (-2))) Total runtime: 80.194 ms So the world is fixed, and we are querying for a rectangular region of tiles. Some more information that might be relevant: All the tiles for a queried region may or may not be present The height and width of a queried rectangle are typically about 10x10-20x20 For any given (world, X) or (world, Y) pair, there may be an unbounded number of matching tiles, but the worst case is currently around 10,000, and typically there are far fewer. New tiles are created far less frequently than existing ones are updated (changing the 'value'), and that itself is far less frequent that just reading as in the query above. The only thing I can think of would be to index on (world, X) and (world, Y). My guess is that the database would be able to take those two sets and intersect them. The problem is that there is a potentially unbounded number of matches for either for either of those. Is there some other kind of index that would be more appropriate?

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  • In SQL, in what situation do we want to Index a field in a table, or 2 fields in a table at the same

    - by Jian Lin
    In SQL, it is obvious that whenever we want to do a search on millions of record, say CustomerID in a Transactios table, then we want to add an index for CustomerID. Is another situation we want to add an index to a field when we need to do inner join or outer join using that field as a criteria? Such as Inner join on t1.custumerID = t2.customerID. Then if we don't have an index on customerID on both tables, we are looking at O(n^2) because we need to loop through the 2 tables sequentially. If we have index on customerID on both tables, then it becomes O( (log n) ^ 2 ) and it is much faster. Any other situation where we want to add an index to a field in a table? What about adding index for 2 fields combined in a table. That is, one index, for 2 fields together?

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  • Index on column with only 2 distinct values

    - by Will
    I am wondering about the performance of this index: I have an "Invalid" varchar(1) column that has 2 values: NULL or 'Y' I have an index on (invalid), as well as (invalid, last_validated) Last_validated is a datetime (this is used for a unrelated SELECT query) I am flagging a small amount of items (1-5%) of rows in the table with this as 'to be deleted'. This is so when i DELETE FROM items WHERE invalid='Y' it does not perform a full table scan for the invalid items. A problem seems to be, the actual DELETE is quite slow now, possibly because all the indexes are being removed as they are deleted. Would a bitmap index provide better performance for this? or perhaps no index at all?

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  • Should I specify both INDEX and UNIQUE INDEX?

    - by Matt Huggins
    On one of my PostgreSQL tables, I have a set of two fields that will be defined as being unique in the table, but will also both be used together when selecting data. Given this, do I only need to define a UNIQUE INDEX, or should I specify an INDEX in addition to the UNIQUE INDEX? This? CREATE UNIQUE INDEX mytable_col1_col2_idx ON mytable (col1, col2); Or this? CREATE UNIQUE INDEX mytable_col1_col2_uidx ON mytable (col1, col2); CREATE INDEX mytable_col1_col2_idx ON mytable (col1, col2);

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  • How to recognize what indexes are not used?

    - by tomaszs
    I have a table in MySQL with 7 indexes, most of them are on more than one column. I think here is too much indexes. Is there any way to get statistics of what indexes are used more by all thousands of queries to this database and what are less worthy so I know what index to consider to remove in first place?

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  • Tell me SQL Server Full-Text searcher is crazy, not me.

    - by Ian Boyd
    i have some customers with a particular address that the user is searching for: 123 generic way There are 5 rows in the database that match: ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY i run a FT query to look for these rows. i'll show you each step as i add more criteria to the search: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') ResidentialAddress1 ========================= 123 MAPLE STREET 12345 TEST 123 MINE STREET 123 GENERIC WAY 123 FAKE STREET ... (30 row(s) affected) Okay, so far so good, now adding the word "generic": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') ResidentialAddress1 ============================= 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY 123 GENERIC WAY (5 row(s) affected) Excellent. And now i'l add the final keyword that the user wants to make sure exists: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"123*"') AND CONTAINS(Patrons.ResidentialAddress1, '"generic*"') AND CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) Huh? No rows? What if i query for just "way*": SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way*"') ResidentialAddress1 ------------------------------ (0 row(s) affected) At first i thought that perhaps it's because of the *, and it's requiring that the root way have more characters after it. But that's not true: Searching for "123*" matches "123" Searching for "generic*" matches "generic" Books online says, The asterisk matches zero, one, or more characters What if i remove the * just for s&g: SELECT ResidentialAddress1 FROM Patrons WHERE CONTAINS(Patrons.ResidentialAddress1, '"way"') Server: Msg 7619, Level 16, State 1, Line 1 A clause of the query contained only ignored words. So one might think that you are just not allowed to even search for way, either alone, or as a root. But this isn't true either: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"way*"') AccountNumber FirstName Lastname ------------- --------- -------- 33589 JOHN WAYNE So sum up, the user is searching for rows that contain all the words: 123 generic way Which i, correctly, translate into the WHERE clauses: SELECT * FROM Patrons WHERE CONTAINS(Patrons.*, '"123*"') AND CONTAINS(Patrons.*, '"generic*"') AND CONTAINS(Patrons.*, '"way*"') which returns no rows. Tell me this just isn't going to work, that it's not my fault, and SQL Server is crazy. Note: i've emptied the FT index and rebuilt it.

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  • Pruning data for better viewing on loglog graph - Matlab

    - by Geodesic
    Hi Guys, just wondering if anyone has any ideas about an issue I'm having. I have a fair amount of data that needs to be displayed on one graph. Two theoretical lines that are bold and solid are displayed on top, then 10 experimental data sets that converge to these lines are graphed, each using a different identifier (eg the + or o or a square etc). These graphs are on a log scale that goes up to 1e6. The first few decades of the graph (< 1e3) look fine, but as all the datasets converge ( 1e3) it's really difficult to see what data is what. There's over 1000 data points points per decade which I can prune linearly to an extent, but if I do this too much the lower end of the graph will suffer in resolution. What I'd like to do is prune logarithmically, strongest at the high end, working back to 0. My question is: how can I get a logarithmically scaled index vector rather than a linear one? My initial assumption was that as my data is lenear I could just use a linear index to prune, which lead to something like this (but for all decades): //%grab indicies per decade ind12 = find(y >= 1e1 & y <= 1e2); indlow = find(y < 1e2); indhigh = find(y > 1e4); ind23 = find(y >+ 1e2 & y <= 1e3); ind34 = find(y >+ 1e3 & y <= 1e4); //%We want ind12 indexes in this decade, find spacing tot23 = round(length(ind23)/length(ind12)); tot34 = round(length(ind34)/length(ind12)); //%grab ones to keep ind23keep = ind23(1):tot23:ind23(end); ind34keep = ind34(1):tot34:ind34(end); indnew = [indlow' ind23keep ind34keep indhigh']; loglog(x(indnew), y(indnew)); But this causes the prune to behave in a jumpy fashion obviously. Each decade has the number of points that I'd like, but as it's a linear distribution, the points tend to be clumped at the high end of the decade on the log scale. Any ideas on how I can do this?

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  • List of all index & index columns in SQL Server DB

    - by Anton Gogolev
    How do I get a list of all index & index columns in SQL Server 2005+? The closest I could get is: select s.name, t.name, i.name, c.name from sys.tables t inner join sys.schemas s on t.schema_id = s.schema_id inner join sys.indexes i on i.object_id = t.object_id inner join sys.index_columns ic on ic.object_id = t.object_id inner join sys.columns c on c.object_id = t.object_id and ic.column_id = c.column_id where i.index_id > 0 and i.type in (1, 2) -- clustered & nonclustered only and i.is_primary_key = 0 -- do not include PK indexes and i.is_unique_constraint = 0 -- do not include UQ and i.is_disabled = 0 and i.is_hypothetical = 0 and ic.key_ordinal > 0 order by ic.key_ordinal which is not exactly what I want. What I want is to list all user-defined indexes (which means no indexes which support unique constraints & primary keys) with all columns (ordered by how do they apper in index definition) plus as much metadata as possible.

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  • Lucene.NET - Find documents that do not contain a specified field

    - by Brandon
    Let's say I have 2 instance of a class called 'Animal'. Animal has 3 fields: Name, Age, and Type The name field is nullable, so before I insert an instance of Animal as a Lucene indexed document, I check if Animal.Name == null, and if it does, I do not insert it as a field in my document. If I were to retrieve all animals, I would see that the Name field does not exist and I can set its value to null. However, there may be situations where I want to say "Get me all animals that do not have a name specified yet." In this situation I want to retrieve all Lucene.NET documents from my animal index that do not contain the Name field. Is there an easy way to do this with Lucene.NET? I want to stay away from having to perform some sort of hack to check if my name field has a value of 'null'.

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  • SQL SERVER - Detecting non-indexed columns but used in WHERE clause

    - by Vadi
    How to detect a column included in WHERE clause but used in indexed? Little Background: Until the time the table has few number of records things will be okay, once it started having millions of records then index should be created for a column which is used in WHERE clauses in stored procs, inline queries etc., Since we have hundreds of stored procs and queries that often gets changed by the devs I wanted to have a automated way of identifying those columns that are used in WHERE clauses but not an index is created. How to do that in SQL SERVER 2008?

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  • jQuery - Finding the element index relative to its container

    - by Hary
    Here's my HTMl structure: <div id="main"> <div id="inner-1"> <img /> <img /> <img /> </div> <div id="inner-2"> <img /> <img class="selected" /> <img /> </div> <div id="inner-3"> <img /> <img /> <img /> </div> </div> What I'm trying to do is get the index of the img.selected element relative to the #main div. So in this example, the index should be 4 (assuming 0 based index) and not 1. My usual way to go about getting indexes is using $element.prevAll().length but, obviously, that will return the index relative to the #inner-2 div. I've tried using $('img.selected').prevAll('#main').length but that's returning 0 :/

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  • Multi-variable indexes in postgres

    - by Jackson Davis
    Im looking at an application where I will be doing quite a few SELECTs where I am trying to find column_a = x AND column_b = y. Is the correct to create that index that something like the following? CREATE INDEX index_name ON table (column_a, column_b)

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  • How to refer to items in Dictionary<string, string> by integer index?

    - by Edward Tanguay
    I made a Dictionary<string, string> collection so that I can quickly reference the items by their string identifier. But I now also need to access this collective by index counter (foreach won't work in my real example). What do I have to do to the collection below so that I can access its items via integer index as well? using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace TestDict92929 { class Program { static void Main(string[] args) { Dictionary<string, string> events = new Dictionary<string, string>(); events.Add("first", "this is the first one"); events.Add("second", "this is the second one"); events.Add("third", "this is the third one"); string description = events["second"]; Console.WriteLine(description); string description = events[1]; //error Console.WriteLine(description); } } }

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  • compare two following values in numpy array

    - by Billy Mitchell
    What is the best way to touch two following values in an numpy array? example: npdata = np.array([13,15,20,25]) for i in range( len(npdata) ): print npdata[i] - npdata[i+1] this looks really messed up and additionally needs exception code for the last iteration of the loop. any ideas? Thanks!

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  • Full-text search in C++

    - by Jen
    I have a database of many (though relatively short) HTML documents. I want users to be able to search this database by entering one or more search words in a C++ desktop application. Hence, I’m looking for a fast full-text search solution. Ideally, it should: Skip common words, such as the, of, and, etc. Support stemming, i.e. search for run also finds documents containing runner, running and ran. Be able to update its index in the background as new documents are added to the database. Be able to provide search word suggestions (like Google Suggest) To illustrate, assume the database has just two documents: Document 1: This is a test of text search. Document 2: Testing is fun. The following words should be in the index: fun, search, test, testing, text. If the user types t in the search box, I want the application to be able to suggest test, testing and text (Ideally, the application should be able to query the search engine for the 10 most common search words starting with t). A search for testing should return both documents. Can you suggest a C or C++ based solution? (I’ve briefly reviewed CLucene and Xapian, but I’m not sure if either will address my needs, especially querying the search word indexes for the suggest feature).

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