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  • About curse of dimensionality

    - by Dan
    My question is about this topic I've been reading about a bit. Basically my understanding is that in higher dimensions all points end up being very close to each other. The doubt I have is whether this means that calculating distances the usual way (euclidean for instance) is valid or not. If it were still valid, this would mean that when comparing vectors in high dimensions, the two most similar wouldn't differ much from a third one even when this third one could be completely unrelated. Is this correct? Then in this case, how would you be able to tell whether you have a match or not?

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  • getting smallest of coordinates that differ by N or more in Python

    - by user248237
    suppose I have a list of coordinates: data = [[(10, 20), (100, 120), (0, 5), (50, 60)], [(13, 20), (300, 400), (100, 120), (51, 62)]] and I want to take all tuples that either appear in each list in data, or any tuple that differs from all tuples in lists other than its own by 3 or less. How can I do this efficiently in Python? For the above example, the results should be: [[(100, 120), # since it occurs in both lists (10, 20), (13, 20), # since they differ by only 3 (50, 60), (51, 60)]] (0, 5) and (300, 400) would not be included, since they don't appear in both lists and are not different from elements in lists other than their own by 3 or less. how can this be computed? thanks.

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  • Conditional PIVOT/transform problem

    - by IanC
    Hi folks I have a table with three columns, which we'll call ID1, ID2, and Value. Sample data: ID ID1 Value 1 1 0 1 2 1 1 3 1 1 3 2 1 4 0 1 4 1 1 5 0 1 5 2 2 1 2 Value is limited to 0, 1, or 2. What I need to do is pivot/transform this data into a column-based count of how many times each possible Value appears, grouped by ID, ID1. The output of the above should be: ID ID1 Val0 Val1 Val2 1 1 1 0 0 1 2 0 2 0 1 3 0 1 1 1 4 1 1 0 1 5 1 0 1 2 1 0 0 1 I'm using SQL Server 2008. How do I do this?

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  • Has inheritance become bad?

    - by mafutrct
    Personally, I think inheritance is a great tool, that, when applied reasonably, can greatly simplify code. However, I seems to me that many modern tools dislike inheritance. Let's take a simple example: Serialize a class to XML. As soon as inheritance is involved, this can easily turn into a mess. Especially if you're trying to serialize a derived class using the base class serializer. Sure, we can work around that. Something like a KnownType attribute and stuff. Besides being an itch in your code that you have to remember to update every time you add a derived class, that fails, too, if you receive a class from outside your scope that was not known at compile time. (Okay, in some cases you can still work around that, for instance using the NetDataContract serializer in .NET. Surely a certain advancement.) In any case, the basic principle still exists: Serialization and inheritance don't mix well. Considering the huge list of programming strategies that became possible and even common in the past decade, I feel tempted to say that inheritance should be avoided in areas that relate to serialization (in particular remoting and databases). Does that make sense? Or am messing things up? How do you handle inheritance and serialization?

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  • What is the best way to restore(rollback) data in an application to a specified state(date) ?

    - by panzerschreck
    Hello, An example would set the context right, the example below captures the various states of the entity, which needs to be reverted(rolled back) . State 1 - Recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 State 2 - Recorded on 02-Mar-2010 Column1 Column2 Data1 0.57 State 3 - Recorded on 03-Mar-2010 Column1 Column2 Data1 0.58 User notices that state3 is not what he intended to be in, decides to revert back to state2. One approach that I can think of, without modifying the entity is via "auditing" all the inserts/updates, as below, the rollback information captures the data just before the updates/modifications on the entity, so that it can be applied in an order when you need to revert.Please note that changing the entity's schema, is not an option. Rollback - R1 recorded on 01-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R2 Recorded on 02-Mar-2010 Column1 Column2 Data1 0.56 Rollback - R3 Recorded on 03-Mar-2010 Column1 Column2 Data1 0.57 So, to get to state2 , we would start with rollback information R1,apply R2 onto it. Is there a better approach to achieve this ? Thanks for your time.

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  • what is the out put?

    - by user329820
    Hi this is my code but when I run it in mysql it will show an error because of datatype but my friend checked it with sql server and it doesn't show error and also insert the value: 32769 .which of them is correct? CREATE TABLE T1 (A INTEGER NOT NULL); INSERT T1 VALUES (32768.5);

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  • EF Query using .Contains() and .ToLowerInvariant() Results in no matches when match is found at the end of a string

    - by MyNameIsJob
    Is it possible to step into a linq query? I have a linq to entity framework 4 query in it's simplest form: List = List.Where(f => f.Value.ToString().ToLowerInvariant().Contains(filter.ToLowerInvariant())); It's a query against an Entity Framework DbContext and I'm having trouble seeing why it works for something like: List searching for 001 yields no results against the following list Test001 Test002 Test003 Test004 However any other search yields results (Such as t00 or Test) Update Basically I'm looking for why a query such as the above wouldn't return a result when I'm using a contains and the value matches the end of a string vs just the middle or begining. It's really confusing. OK, it appears to have something to do with ToLowerInvariant() - when I removed that method it works just fine.

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  • References/walkthroughs for maintaining database schemas with Visual Studio 2010?

    - by user206356
    I have Visual Studio 2010 Beta 2 and SQL Server 2008 installed. I'm working with a populated database and want to modify various column types. SQL Server Management Studio requires me to drop tables to do this, and get pretty finicky given my moderate level of knowledge of SQL Server. However, I heard the new database project type supports changing the database schema to the desired format and it will handle creating and running all the scripts to implement the changes. I've created a VS2010 database project using the existing database as the source, but so far haven't had much luck figuring out the appropriate method to make the changes without getting an error. As a result, I'm looking for any reference info I can find on using VS2010's capabilities in this area. Any suggestions?

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  • Difference between dates when grouping in SQL

    - by CeejeeB
    I have a table of purchases containing a user_id and a date_of_purchase. I need to be able to select all the users who have made 2 purchases within 12 months of each other. The dates can be any point in time as long as they are less than 12 months apart. e.g. user_id date_of_purchase 123 01/Jan/2010 124 01/Aug/2010 123 01/Feb/2010 124 05/Aug/2008 In this example i want user_id 123

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  • Is this safe? Is this OK to do in MYSQL?

    - by alex
    I have always done this: mysqldump -hlocalhost -uuser -ppass MYDATABASE > /home/f/db_backup/MYDATABASE.sql mysql -uuser -ppass MYDATABASE < MYDATABASE.sql But, if I do this instead...is this safe? Is this identical to the above??? mysqldump -hlocalhost -uuser -ppass MYDATABASE | gzip > /home/f/db_backup/MYDATABASE.sql.gz zcat MYDATABASE.sql.gz | mysql -uuser -ppass MYDATABASE

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  • Table naming convention?

    - by MattSlay
    In our manufacturing shop, each Employee hits the time clock every time they change Jobs or Machines (work centers) during their work day. Each record created in the Time Clock app has foreign keys that link the record to: the Employee, the Job, and the Machine which they are about to operate. I’m trying to determine the best name for this table… If I were tempted to call it ClockRecords or TimeClockRecords, why wouldn’t I also consider naming it JobTimeRecords, or why not MachineTimeRecords. Any ideas on a good name?

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  • Using SQL Server for web applications

    - by rem
    As far as I understand, due to license reqirements all web applications, which use MS SQL Server, use SQL Server Express (free) or SQL Server web edition (processor license). Is it so? What are other specific features of SQL Server usage for web app?

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  • How to handle ids and polymorphic associations in views if compound keys are not supported?

    - by duncan
    I have a Movie plan table: movie_plans (id, description) Each plan has items, which describe a sequence of movies and the duration in minutes: movie_plan_items (id, movie_plan_id, movie_id, start_minutes, end_minutes) A specific instance of that plan happens in: movie_schedules (id, movie_plan_id, start_at) However the schedule items can be calculated from the movie_plan_items and the schedule start time by adding the minutes create view movie_schedule_items as select CONCAT(p.id, '-', s.id) as id, s.id as movie_schedule_id, p.id as movie_plan_item_id, p.movie_id, p.movie_plan_id, (s.start_at + INTERVAL p.start_minutes MINUTE) as start_at, (s.start_at + INTERVAL p.end_minutes MINUTE) as end_at from movie_plan_items p, movie_schedules s where s.movie_plan_id=p.movie_plan_id; I have a model over this view (readonly), it works ok, except that the id is right now a string. I now want to add a polymorphic property (like comments) to various of the previous tables. Therefore for movie_schedule_items I need a unique and persistent numeric id. I have the following dilemma: I could avoid the id and have movie_schedule_items just use the movie_plan_id and movie_schedule_id as a compound key, as it should. But Rails sucks in this regard. I could create an id using String#hash or a md5, thus making it slower or collision prone (and IIRC String#hash is no longer persistent across processes in Ruby 1.9) Any ideas on how to handle this situation?

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  • Spotlight query to search for all archives and ISO files that their names do not end in bin

    - by Bytecode Ninja
    The following Spotlight query, correctly returns all archive and ISO files on my system: kind:iso OR kind:archive However, Spotlight treats .bin files as archives too and returns .bin files in the results as well. How can I modify the above query and exclude files that end in bin from the result? I tried the following query but it is not working: (kind:iso OR kind:archive) AND NOT name:*bin Thanks in advance.

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  • How to get only one record for each duplicate rows of the id in oracle?

    - by Psychocryo
    suppose i have this table: group_id | image | image_id | ----------------------------- 23 blob 1 23 blob 2 23 blob 3 21 blob 4 21 blob 5 25 blob 6 25 blob 7 how to get results of only 1 of each group id? in this case,there may be multiple images for one group id, i just want one result of each group_id i tried distinct but i will only get group_id. max for image also would not work.

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  • Embedded analog of CouchDB, same as sqlite for SQL Server

    - by Mike Chaliy
    I like an idea of document oriented databases like CouchDB. I am looking for simple analog. My requirements is just: persistance storage for schema less data; some simple in-proc quering; good to have transactions and versioning; ruby API; map/reduce is aslo good to have; should work on shared hosting What I do not need is REST/HTTP interfaces (I will use it in-proc). Also I do not need all scalability stuff.

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  • What is the most efficient way to store and access images

    - by MT
    I am working on a project which has to store tens and thousands of images on a server and let the users access them. I need the most efficient method to store these images and to retrieve them. Also, I need information about which technology I should opt. I haven't started the project yet. So, I am thinking between PHP w/ CodeIgniter and Ruby on Rails. PS: The site is something similar to Flickr except that the images are uploaded only by the Authors of the content, and not by the users.

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