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  • SQL -- How is DISTINCT so fast without an index?

    - by Jonathan
    Hi, I have a database with a table called 'links' with 600 million rows in it in SQLite. There are 2 columns in the database - a "src" column and a "dest" column. At present there are no indices. There are a fair number of common values between src and dest, but also a fair number of duplicated rows. The first thing I'm trying to do is remove all the duplicate rows, and then perform some additional processing on the results, however I've been encountering some weird issues. Firstly, SELECT * FROM links WHERE src=434923 AND dest=5010182. Now this returns one result fairly quickly and then takes quite a long time to run as I assume it's performing a tablescan on the rest of the 600m rows. However, if I do SELECT DISTINCT * FROM links, then it immediately starts returning rows really quickly. The question is: how is this possible?? Surely for each row, the row must be compared against all of the other rows in the table, but this would require a tablescan of the remaining rows in the table which SHOULD takes ages! Any ideas why SELECT DISTINCT is so much quicker than a standard SELECT?

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  • rails separate login for an api

    - by Squadrons
    I have a very simple api that is part of a rails app that requires logging in. I just need a way to make the api part accessible with a simple form that allows the user to enter parameters like a key (just a simple one stored in the DB, no OAuth or anything), a userId to find and return a user via json, and maybe some other parameters like asking for their schedule. How can I keep this seperate from the rest of the app, making it a public facing form that will grant access only to the api? Thanks.

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  • Hibernate many-to-many relationship

    - by Capitan
    I have two mapped types, related many-to-many. @Entity @Table(name = "students") public class Student{ ... @ManyToMany(fetch = FetchType.EAGER) @JoinTable( name = "students2courses", joinColumns = { @JoinColumn( name = "student_id", referencedColumnName = "_id") }, inverseJoinColumns = { @JoinColumn( name = "course_id", referencedColumnName = "_id") }) public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } ... } __ @Entity @Table(name = "courses") public class Course{ ... @ManyToMany(fetch = FetchType.EAGER, mappedBy = "courses") public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } ... } But if I update/delete Course entity, records are not created/deleted in table students2courses. (with Student entity updating/deleting goes as expected) I wrote abstract class HibObject public abstract class HibObject { public String getRemoveMTMQuery() { return null; } } which is inherited by Student and Course. In DAO I added this code (for delete() method): String query = obj.getRemoveMTMQuery(); if (query != null) { session.createSQLQuery(query).executeUpdate(); } and I ovrerided method getRemoveMTMQuery() for Course @Override @Transient public String getRemoveMTMQuery() { return "delete from students2courses where course_id = " + id + ";"; } Now it works but I think it's a bad code. Is there a best way to solve this problem?

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  • Automatically Persisting a Complex Java Object

    - by VeeArr
    For a project I am working on, I need to persist a number of POJOs to a database. The POJOs class definitions are sometimes highly nested, but they should flatten okay, as the nesting is tree-like and contains no cycles (and the base elements are eventually primitives/Strings). It is preferred that the solution used create one table per data type and that the tables will have one field per primitive member in the POJO. Subclassing and similar problems are not issues for this particular project. Does anybody know of any existing solutions that can: Automatically generate a CREATE TABLE definition from the class definition Automatically generate a query to persist an object to the database, given an instance of the object Automatically generate a query to retrieve an object from the database and return it as a POJO, given a key. Solutions that can do this with minimum modifications/annotions to the class files and minimum external configuration are preferred. Example: Java classes //Class to be persisted class TypeA { String guid; long timestamp; TypeB data1; TypeC data2; } class TypeB { int id; int someData; } class TypeC { int id; int otherData; } Could map to CREATE TABLE TypeA ( guid CHAR(255), timestamp BIGINT, data1_id INT, data1_someData INT, data2_id INt, data2_otherData INT ); Or something similar.

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  • How should I mock out my data connectivity

    - by BobTheBuilder
    I'm trying to unit test my Data Access Layer and I'm in the process of trying to mock my data connectivity to unit test my DAL and I'm coming unstuck trying to mock out the creation of the commands. I thought about using a queue of IDbParameters for the creation of the parameters, but the unit tests then require that the parameters are configured in the right order. I'm using MOQ and having looked around for some documentation to walk me through this, I'm finding lots of recommendation not to do this, but to write a wrapper for the connection, but it's my contention that my DAL is supposed to be the wrapper for my database and I don't feel I should be writing wrappers... if I do, how do I unit test the connectivity to the database for my wrapper? By writing another wrapper? It seems like it's turtles all the way down. So does anyone have any recommendations or tutorials regarding this particular area of unit testing/mocking?

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  • HTML5 card game [closed]

    - by ChrisCa
    I created a card game in silverlight a year or so ago in order to learn a bit about Silverlight. I am now wanting to make a HTML5 version of the game in an effort to learn a little bit more about that. I am thinking I'd like to take advantage of stuff like Knockout.js and WebSockets and the canvas element. Now what I'm confused about is how to lay out the cards on the screen. With Silverlight I was able to make a "Hand" control, which was made up of two sub controls - the cards the player has in their hand and the ones they have on the table. And they in turn were made up of Card controls. Now I don't believe there is the concept on a User Control in javascript. So I am possibly thinking about this in entirely the wrong way. So my question is - how could I lay out some cards on the table and perhaps make reuse of something for each player? I have a client side JSON object called game, which contains an array of players. Each player has a hand which is made up of an array of in-hand cards and on-table cards. Ideally I would like to bind these to something using Knockout.js - but I don't know what I could bind to. Would I simply position images (of cards) on a canvas? Is there a way to make some kind of Hand object that each player could have and that I could bind to? Any advice? Or sample code you've seen elsewhere?

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  • Creating methods with infinite overloads ? (.NET)

    - by MarceloRamires
    In C# you can do this: foo = string.Format("{0} {1} {2} {3} ...", "aa", "bb", "cc" ...); This method Format() accepts infinite parameters, being the first one how the string should be formatted and the rest are values to be put in the string. Today I've come to a situation where I had to get a set of strings and test them, then I remembered this language functionality, but I had no clue. After a few unsuccessful web searches, I've realised it would be more prudent to just get an array, which didn't make me quite satisfied. Q: How do I make a function that accepts infinite parameters? And how do I use it ?

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  • How do I compare 2 fields and return the lowest value of each record?

    - by BigRob
    I'm slowly learning access to make a database of products and suppliers for my parents' business. What i've got is a table of products indexed by our product reference and 2 more tables for 2 different suppliers that contains the suppliers product reference and price that links with our reference. I've made a query that performs a left outer join such that it returns a table of our products with each supplier's reference and price, i.e: Ref | Product Name | Supplier 1 Ref | Supplier 1 Price | Supplier 2 Ref | Supplier 2 Price Here's the query I used: SELECT Catalog.Ref, Catalog.[Product Name], Catalog.Price, [D Products].[Supplier Ref], [D Products].Cost, [GS Products].[Supplier Ref], [GS Products].Cost FROM ([Catalog] LEFT JOIN [D Products] ON Catalog.Ref = [D Products].Ref) LEFT JOIN [GS Products] ON Catalog.Ref = [GS Products].Ref; Not all products are available from both suppliers, hence the outer join. What I want to do (with a query?) is to take the table produced by the query above and simply show the product reference, cheapest supplier reference and cheapest supplier price, i.e: Ref | Cheapest Suppplier Ref | Cheapest Supplier Price Unfortunately my SQL knowledge isn't quite good enough to figure this out, but if anyone can help i'd really appreciate it. Thanks, Rob

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  • Preserving NULL values in a Double Variable

    - by Sam
    Hi, I'm working on a vb.net application which imports from an Excel spreadsheet. If rdr.HasRows Then Do While rdr.Read() If rdr.GetValue(0).Equals(System.DBNull.Value) Then Return Nothing Else Return rdr.GetValue(0) End If Loop Else I was using string value to store the double values and when preparing the database statement I'd use this code: If (LastDayAverage = Nothing) Then command.Parameters.AddWithValue("@WF_LAST_DAY_TAG", System.DBNull.Value) Else command.Parameters.AddWithValue("@WF_LAST_DAY_TAG", Convert.ToDecimal(LastDayAverage)) End If I now have some data with quite a few decimal places and the data was put into the string variable in scientific notation, so this seems to be the wrong approach. It didn't seem right using the string variable to begin with. If I use a double or decimal type variable, the blank excel values come across as 0.0. How can I preserve the blank values? Thanks

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  • ASP.NET MVC: How to show value in a label from selected Drop Down List item?

    - by Lillie
    Hi! I'm trying to show a value of selected Drop Down List item in a label. I managed to make this work with Web Forms but with MVC I'm totally lost. My Index looks like this: [...] <% using (Html.BeginForm()) { %> <table> <tr> <td>Processor</td> <td><%= Html.DropDownList("lstProcessor1", new SelectList((IEnumerable)ViewData["Processor1List"], "product_price", "product_description")) %></td> </tr> <tr> <td>Total Amount</td> <td>0,00 €</td> </tr> </table> <input type="submit" value="Submit" /> <% } %> [...] And my HomeController starts with: using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Mvc; using System.Web.Mvc.Ajax; using MvcApplication1.Models; namespace MvcApplication1.Controllers { [HandleError] public class HomeController : Controller { // Connect database DB50DataContext _ctx = new DB50DataContext(); // GET: /Home/ public ActionResult Index() { // Search: Processors var products = from prod in _ctx.products where prod.product_searchcode == "processor1" select prod; ViewData["Processort1List"] = products; return View(); } I would like the product_price to show on the second line of the table, where it now says 0,00 €. It should also update the price automatically when the item from the Drop Down List is changed. I guess I should use JQuery but I have no idea how. Could someone please give me some tips how to do this?

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  • Adding up row number and displaying total using COUNT (PHP MySQL)

    - by Yvonne
    I'm attempting to run a query that adds up the total number of subjects in a class. A class has many subjects. There is a 'teachersclasses' table between teachers (the user table) and classes. The principles sounds pretty simple but I'm having some trouble in getting my page to display the number of subjects for each class (directly associated with the teacher) This is what I have so far, trying to make use of the COUNT with a nested SELECT: SELECT (SELECT count(*) FROM subjects WHERE subjects.classid = class.classid) AS total_subjects, class.classname, class.classid FROM class Then I am calling up 'num_subjects' to present the total within a while loop: <?php echo $row['total_subjects']?> From the above, I am receiving the total subjects for a class, but within the same table row (for one class) and my other while loop doesnt run anymore, which returns all of the classes associated with a teacher :( ... Bit of a mess now! I know to return the classes for a particular teacher, I can do an additional WHERE clause on the session of 'teacherid' but I think my query is getting too complicated for me that errors are popping up everywhere. Anyone have a quick fix for this! Thanks very much

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  • '<=' operator is not working in sql server 2000

    - by Lalit
    Hello, Scenario is, database is in the maintenance phase. this database is not developed by ours developer. it is an existing database developed by the 'xyz' company in sql server 2000. This is real time database, where i am working now. I wanted to write the stored procedure which will retrieve me the records From date1 to date 2.so query is : Select * from MyTableName Where colDate>= '3-May-2010' and colDate<= '5-Oct-2010' and colName='xyzName' whereas my understanding I must get data including upper bound date as well as lower bound date. but somehow I am getting records from '3-May-2010' (which is fine but) to '10-Oct-2010' As i observe in table design , for ColDate, developer had used 'varchar' to store the date. i know this is wrong remedy by them. so in my stored procedure I have also used varchar parameters as @FromDate1 and @ToDate to get inputs for SP. this is giving me result which i have explained. i tried to take the parameter type as 'Datetime' but it is showing error while saving/altering the stored procedure that "@FromDate1 has invalid datatype", same for "@ToDate". situation is that, I can not change the table design at all. what i have to do here ? i know we can use user defined table in sql server 2008 , but there is version sql server 2000. which does not support the same. Please guide me for this scenario. **Edited** I am trying to write like this SP: CREATE PROCEDURE USP_Data (@Location varchar(100), @FromDate DATETIME, @ToDate DATETIME) AS SELECT * FROM dbo.TableName Where CAST(Dt AS DATETIME) >=@fromDate and CAST(Dt AS DATETIME)<=@ToDate and Location=@Location GO but getting Error: Arithmetic overflow error converting expression to data type datetime. in sql server 2000 What should be that ? is i am wrong some where ? also (202 row(s) affected) is changes every time in circular manner means first time sayin (122 row(s) affected) run again saying (80 row(s) affected) if again (202 row(s) affected) if again (122 row(s) affected) I can not understand what is going on ?

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  • The big last_insert_id() problem, again.

    - by wretrOvian
    Note - this follows my question here: http://stackoverflow.com/questions/2983685/jdbc-does-the-connection-break-if-i-lose-reference-to-the-connection-object Now i have a created a class so i can deal with JDBC easily for the rest of my code - public class Functions { private String DB_SERVER = ""; private String DB_NAME = "test"; private String DB_USERNAME = "root"; private String DB_PASSWORD = "password"; public Connection con; public PreparedStatement ps; public ResultSet rs; public ResultSetMetaData rsmd; public void connect() throws java.io.FileNotFoundException, java.io.IOException, SQLException, Exception { String[] dbParms = Parameters.load(); DB_SERVER = dbParms[0]; DB_NAME = dbParms[1]; DB_USERNAME = dbParms[2]; DB_PASSWORD = dbParms[3]; // Connect. Class.forName("com.mysql.jdbc.Driver").newInstance(); con = DriverManager.getConnection("jdbc:mysql://" + DB_SERVER + "/" + DB_NAME, DB_USERNAME, DB_PASSWORD); } public void disconnect() throws SQLException { // Close. con.close(); } } As seen Parameters.load() refreshes the connection parameters from a file every-time, so that any changes to the same may be applied on the next immediate connection. An example of this class in action - public static void add(String NAME) throws java.io.FileNotFoundException, java.io.IOException, SQLException, Exception { Functions dbf = new Functions(); dbf.connect(); String query = "INSERT INTO " + TABLE_NAME + "(" + "NAME" + ") VALUES(?)"; PreparedStatement ps = dbf.con.prepareStatement(query); ps.setString(1, NAME); ps.executeUpdate(); dbf.disconnect(); } Now here is the problem - for adding a record to the table above, the add() method will open a connection, add the record - and then call disconnect() . What if i want to get the ID of the inserted record after i call add() -like this : Department.add("new dept"); int ID = getlastID(); Isn't it possible that another add() was called between those two statements?

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  • Count function calls by name or signature. Gcc, C++

    - by MajesticRa
    I have some c++ written package. Linux, gcc. I can modify compilation process (change Makefile, flags, etc.), but can not change C++ source code. One runs the package with different parameters, it does a job and exits. How to count: 1) Number of calls of function with specific name? 2) Number of calls of functions with specific signature? 3) Number of calls of functions where one of the parameters is of specific type i.e. std::string (type is specified by signature)? 4) and extra Number of calls of functions of STL objects, i.e. std::string copy constructor? (I mean count a number of calls during the run. ) I thought to do it with GDB, but I found it very tough to do (1) and have not found how to do (2)-(4) at all. All acceptable answers I will write here for humanity.

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  • MySQL null/empty-string too long for VarChar(5) ?

    - by rlb.usa
    I have a stored procedure that takes an input var_zip varchar(5). My webapp calls this procedure and gives it the parameter: cmd.Parameters.Add(new MySqlParameter("var_Zip", MySqlDbType.VarChar, 5)); cmd.Parameters["var_Zip"].Value = txtZip.Text; txtZip is empty. So it is either giving empty string '', or null. Doesn't matter to me which. But it is throwing an error: MySql.Data.MySqlClient.MySqlException: Data too long for column 'var_Zip' at row 1 What's going on and how can I fix it? I don't understand.

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  • Bind data of interface properties only

    - by nivpenso
    I am new in all the Entity Framework models and the data bindings. I created an interface and generated a model class from my Candidate table in the db. public interface ICandidate { String ID { get; set; } string Name { get; set; } string Mail { get; set; } } i created a partial class to the generated Candidate model so i will be able to implement the ICandidate interface without changing any generated code. public partial class Candidates : ICandidate { string ICandidate.ID { get { return this.PK; } set { _PK = value; } } string ICandidate.Name { get{ return this._Name; } set { _Name = value; } } string ICandidate.Mail { get { return this._Email; } set { this._Email = value; } } } Of course, the generated class has more properties than the interface has (Like IsDeleted field that is not necessary for the interface). I want to display in a DataGridView all the candidates from the db. But I want that only the interface's properties will be shown as columns in the DataGridView. Is there a way bind only the interface's properties the the DataGridView? In my DB there is a table called Candidate_To_Company with these columns: PK, Candidate_FK, Company_FK, Insertion_Date I would like to bind this table to DataGridView. but instead of displaying Candidate_FK i would like to display the candidate name from ICandidate. Is this possible?

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  • Update all but one result?

    - by Jack M.
    I'm trying to update a table to remove all but the first instance of a group. Basically, I have a table with vehicle data related to an insurance policy. Each policy should only have one power_unit. Everything else should be a towed unit. Unfortunately, a bug has been duplicating power units, and now I need to clean this up. There are ~10k records in the database, and ~4k of them have doubled up power units. The important bits of my table (call it test1 for now) are: +------------+---------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+---------+------+-----+---------+----------------+ | id | int(10) | NO | PRI | NULL | auto_increment | | policy_id | int(10) | NO | | NULL | | | power_unit | int(1) | NO | | 0 | | +------------+---------+------+-----+---------+----------------+ And some sample data: +----+-----------+------------+ | id | policy_id | power_unit | +----+-----------+------------+ | 1 | 1 | 1 | | 2 | 1 | 1 | | 3 | 1 | 1 | | 4 | 2 | 1 | | 5 | 2 | 1 | | 6 | 2 | 1 | | 7 | 4 | 1 | | 8 | 4 | 1 | | 9 | 4 | 1 | | 10 | 5 | 1 | | 11 | 5 | 1 | | 12 | 6 | 1 | +----+-----------+------------+ Basically I'd like to end up where policy_id 1 has only one power_unit=1. Same for policy_id 2, 3, 4, etc. For policy_id 6, nothing should change (there is only one entry, and it is a power_unit already). I don't know if this is possible, but it was an intriguing problem for me, so I thought you guys might find it the same.

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  • mysql report sql help

    - by sfgroups
    I have mysql table with data like this. record will have server with total cpu and virtual server with cpu assinged type, cpu srv1, 10 vsrv11, 2 vsrv12, 3 srv2, 15 vsrv21, 6 vsrv22, 7 vsrv23, 1 from the above data, I want to create output like this. server, total cpu, assigned cpu, free cpu srv1, 10, 5, 5 srv2, 15, 14, 1 Can you help me on creating sql query for this report? I have changed my table and data like this. CREATE TABLE `cpuallocation` ( `servertype` varchar(10) DEFAULT NULL, `servername` varchar(20) DEFAULT NULL, `hostname` varchar(20) DEFAULT NULL, `cpu_count` float DEFAULT NULL, UNIQUE KEY `server_uniq_idx` (`servertype`,`servername`,`hostname`) insert into cpuallocation values('srv', 'server1', '',16); insert into cpuallocation values('vir', 'server1', 'host1',5); insert into cpuallocation values('vir', 'server1', 'host2',2.5); insert into cpuallocation values('vir', 'server1', 'host3',4.5); insert into cpuallocation values('srv', 'server2', '',8); insert into cpuallocation values('vir', 'server2', 'host1',5); insert into cpuallocation values('vir', 'server2', 'host2',2.5); insert into cpuallocation values('srv', 'server3', '',24); insert into cpuallocation values('vir', 'server3', 'host1',12); insert into cpuallocation values('vir', 'server3', 'host2',2); insert into cpuallocation values('srv', 'server4', '',12); Update: I created two view, now I getting the result I want. create view v1 as select servername, sum(cpu_count) as cpu_allocated from cpuallocation where servertype='vir' group by servername; create view v2 as select servername, cpu_count as total_cpu from cpuallocation where servertype='srv'; select a.servername, a.total_cpu, b.cpu_allocated from v2 as a left join v1 as b on a.servername=b.servername; +------------+-----------+---------------+ | servername | total_cpu | cpu_allocated | +------------+-----------+---------------+ | server1 | 16 | 12 | | server2 | 8 | 7.5 | | server3 | 24 | 14 | | server4 | 12 | NULL | +------------+-----------+---------------+ 4 rows in set (0.00 sec) Is it possible to create a query with-out creating views?

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  • find a duplicate series in SQL

    - by SomeMiscGuy
    I have a table with 3 columns containing a variable number of records based off of the first column which is a foreign key. I am trying to determine if I can detect when there is a duplicate across multiple rows for an entire series declare @finddupseries table ( portid int, asset_id int, allocation float ) ; INSERT INTO @finddupseries SELECT 250, 6, 0.05 UNION ALL SELECT 250, 66, 0.8 UNION ALL SELECT 250, 2, 0.105 UNION ALL SELECT 250, 4, 0.0225 UNION ALL SELECT 250, 5, 0.0225 UNION ALL SELECT 251, 13, 0.6 UNION ALL SELECT 251, 2, 0.3 UNION ALL SELECT 251, 5, 0.1 UNION ALL SELECT 252, 13, 0.8 UNION ALL SELECT 252, 2, 0.15 UNION ALL SELECT 252, 5, 0.05 UNION ALL SELECT 253, 13, 0.4 UNION ALL SELECT 253, 2, 0.45 UNION ALL SELECT 253, 5, 0.15 UNION ALL SELECT 254, 6, 0.05 UNION ALL SELECT 254, 66, 0.8 UNION ALL SELECT 254, 2, 0.105 UNION ALL SELECT 254, 4, 0.0225 UNION ALL SELECT 254, 5, 0.0225 select * from @finddupseries The records for portid 250 and 254 match. Is there any way I can write a query to detect this? edit: yes, the entire series must match. Also, if there was a way to determine which one it DID match would be helpful as the actual table has around 10k records. thanks!

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  • Using ddply() to Get Frequency of Certain IDs, by Appearance in Multiple Rows (in R)

    - by EconomiCurtis
    Goal If the following description is hard follow, please see the example "before" and "after" to see a straightforward example. I have bartering data, with unique trade ids, and two sides of the trade. Side1 and Side2 are baskets, lists of item ids that represent both sides of the barter transaction. I'd like to count the frequency each ITEM appears in TRADES. E.g, if item "001" appeared in 3 trades, I'd have a count of 3 (ignoring how many times the item appeared in each trade). Further, I'd like to do this with the plyr ddply function. (If you're interested as to my motivation, I working over many hundreds of thousands of transactions and am already using a ddply to calculate several other summary statistics. I'd like to add this to the ddply I'm already using, rather than calculate it after, and merge it into the ddply output.... sorry if that was difficult to follow.) In terms of pseudo code I'm working off of: merge each row of Side1 and Side2 by row, get unique() appearances of each item id apply table() function transpose and relabel output from table Example of the structure of my data, and the output I desire. Data Example (before): df <- data.frame(TradeID = c("01","02","03","04")) df$Side1 = list(c("001","001","002"), c("002","002","003"), c("001","004"), c("001","002","003","004")) df$Side2 = list(c("001"),c("007"),c("009"),c()) Desired Output (after): df.ItemRelFreq_byTradeID <- data.frame(ItemID = c("001","002","003","004","007","009"), RelFreq_byTrade = c(3,3,2,2,1,1)) One method to do this without ddply I've worked out one way to do this below. My problem is that I can't quite seem to get ddply to do this for me. temp <- table(unlist(sapply(mapply(c,df$Side1,df$Side2), unique))) df.ItemRelFreq_byTradeID <- data.frame(ItemID = names(temp), RelFreq_byTrade = temp[]) Thanks for any help you can offer! Curtis

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  • How to identify each parameter type in a C# method?

    - by user465876
    I have a C# method say: MyMethod(int num, string name, Color color, MyComplexType complex) Using reflection, how can I distinctly identify each of the parameter types of any method? I want to perform some task by parameter type. If the type is simple int, string or boolean then I do something, if it is Color, XMLDocument, etc I do something else and if it is user defined type like MyComplexType or MyCalci etc then I want to do certain task. I am able to retrieve all the parameters of a method using ParameterInfo and can loop through each parameter and get their types. But how can I identify each data type? foreach (var parameter in parameters) { //identify primitive types?? //identify value types //identify reference types } Edit: this is apart of my code to create a propert grid sort of page where I want to show the parameter list with data types for the selected method. If the parameter has any userdefined type/reference type then I want to expand it further to show all the elements under it with datatypes.

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  • Is my approach for persistent login secure ?

    - by Jay
    I'm very much stuck with the reasonable secure approach to implement 'Remember me' feature in a login system. Here's my approach so far, Please advice me if it makes sense and is reasonably secure: Logging: User provides email and password to login (both are valid).. Get the user_id from DB Table Users by comparing provided email Generate 2 random numbers hashed strings: key1, key2 and store in cookies. In DB Table COOKIES, store key1, key2 along with user_id. To Check login: If key1 and key2 both cookies exist, validate both keys in DB Table COOKIES (if a row with key1, and key2 exists, user is logged). if cookie is valid, regenrate key2 and update it in cookie and also database. Why re-genrating key: Because if someone steals cookie and login with that cookie, it will be working only until the real user login. When the real user will login, the stolen cookie will become invalid. Right? Why do I need 2 keys: Because if i store user_id and single key in cookie and database, and the user want to remember the password on another browser, or computer, then the new key will be updated in database, so the user's cookie in earlier browser/PC will become invalid. User wont be able to remember password on more than one place. Thanks for your opinions.

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  • Strange PHP array behavior overwriting values with all the same values

    - by dasdas
    Im doing a simple mysqli query with code ive used many times before but have never had this problem happen to me. I am grabbing an entire table with an unknown number of columns (it changes often so i dont know the exact value, nor the column names). I have some code that uses metadata to grab everything and stick it in an array. This all works fine, but the output is messed up: $stmt -> execute(); //the query is legit, no problems there $meta = $stmt->result_metadata(); while ($field = $meta->fetch_field()) { $params[] = &$row[$field->name]; } call_user_func_array(array($stmt, 'bind_result'), $params); while ($stmt->fetch()) { $pvalues[++$i] = $row; //$pvalues is an array of arrays. row is an array //print_r($row); print_r($pvalues[$i-1]); } $stmt -> close(); I would assume that $pvalues has the results that I am looking for. My table currently has 2 rows. $pvalues has array length 2. Both rows in $pvalues are exactly the same. If i use the: print_r($row) it prints out the correct values for both rows, but if later on i check what is in $pvalues it is incorrect (1 row is assigned to both indices of $pvalues). If i use the print_r($pvalues[$i-1]) it prints exactly as I expect, the same row in the table twice. Why isnt the data getting assigned to $pvalues? I know $row holds the right information at one point, but it is getting overwritten or lost.

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  • hash tables and 2d vectors

    - by Sunil
    I want to push a 2d vector into a hash table row by row and later search for a row (vector) in the hash table and want to be able to find it. I want to do something like #include <iostream> #include <set> #include <vector> using namespace std; int main(){ std::set < vector<int> > myset; vector< vector<int> > v; int k = 0; for ( int i = 0; i < 5; i++ ) { v.push_back ( vector<int>() ); for ( int j = 0; j < 5; j++ ) v[i].push_back ( k++ ); } for ( int i = 0; i < 5; i++ ) { std::copy(v[i].begin(),v[i].end(),std::inserter(myset)); // This is not correct but what is the right way ? // and also here, I want to search for a particular vector if it exists in the table. for ex. the second row of vector v. } return 0; } I'm not sure how to insert and look up a vector in a set. So if nybody could guide me, it will be helpful. Thanks

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  • Good JDBC pattern

    - by Java Developer
    What is the good practice for database operation in Java application? Do you construct the DML syntax in the Java code and send the statements to DB engine for execution, or you just collect the parameters and then make a call to stored procedure with the parameters via java code? or neither because that's just not how to do it? can anyone give an example of a full database utility classes to do database operations in Java app? also what about the transaction manager? My assignment is to make database operation that is modular in Java. Thanks

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