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• Dynamic Multiple Choice (Like a Wizard) - How would you design it? (e.g. Schema, AI model, etc.)

  - by henry74

  This question can probably be broken up into multiple questions, but here goes... In essence, I'd like to allow users to type in what they would like to do and provide a wizard-like interface to ask for information which is missing to complete a requested query. For example, let's say a user types: "What is the weather like in Springfield?" We recognize the user is interested in weather, but it could be Springfield, Il or Springfield in another state. A follow-up question would be: What Springfield did you want weather for? 1 - Springfield, Il 2 - Springfield, Wi You can probably think of a million examples where a request is missing key data or its ambiguous. Make the assumption the gist of what the user wants can be understood, but there are missing pieces of data required to complete the request. Perhaps you can take it as far back as asking what the user wants to do and "leading" them to a query. This is not AI in the sense of taking any input and truly understanding it. I'm not referring to having some way to hold a conversation with a user. It's about inferring what a user wants, checking to see if there is an applicable service to be provided, identifying the inputs needed and overlaying that on top of what's missing from the request, then asking the user for the remaining information. That's it! :-) How would you want to store the information about services? How would you go about determining what was missing from the input data? My thoughts: Use regex expressions to identify clear pieces of information. These will be matched to the parameters of a service. Figure out which parameters do not have matching data and look up the associated question for those parameters. Ask those questions and capture answers. Re-run the service passing in the newly captured data. These would be more free-form questions. For multiple choice, identify the ambiguity and search for potential matches ranked in order of likelihood (add in user history/preferences to help decide). Provide the top 3 as choices. Thoughts appreciated. Cheers, Henry

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• Can django lazy-load fields in a model?

  - by Leopd

  One of my django models has a large TextField which I often don't need to use. Is there a way to tell django to "lazy-load" this field? i.e. not to bother pulling it from the database unless I explicitly ask for it. I'm wasting a lot of memory and bandwidth pulling this TextField into python every time I refer to these objects. The alternative would be to create a new table for the contents of this field, but I'd rather avoid that complexity if I can.

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• CakePHP HABTM Plugin table naming conventions (for 1.3)

  - by Parris

  Hi everyone, I know naming conventions for tables used by plugins generally start with the name of the plugin and then the model pluralized. For example lets say I had a plugin called Poll, with a model also called PollPoll and another model called PollTag then the resulting table names would be poll_polls and poll_tags. They would also have a habtm relationship so what is the convention for that table name? I believe it would poll_poll_polls_poll_tags, although it is a little redundant it makes sense since the first poll_ represents the name of the plugin, while poll_polls and poll_tags relates to the models. Also have any naming conventions changed for plugins in 1.3? Is the above stated correct? Thanks!

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• Ruby on Rails: Simple way to select all records of a nested model?

  - by Josh Pinter

  Just curious, I spent an embarrassing amount of time trying to get an array of all the records in a nested model. I just want to make sure there is not a better way. Here is the setup: I have three models that are nested under each other (Facilities Tags Inspections), producing code like this for routes.rb: map.resources :facilities do |facilities| facilities.resources :tags, :has_many => :inspections end I wanted to get all of the inspections for a facility and here is what my code ended up being: def facility_inspections @facility = Facility.find(params[:facility_id]) @inspections = [] @facility.tags.each do |tag| tag.inspections.each do |inspection| @inspections << inspection end end end It works but is this the best way to do this - I think it's cumbersome. Thanks in advance. Josh

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• Saving related model objects

  - by iHeartDucks

  I have two related models (one to many) in my django app and When I do something like this ObjBlog = Blog() objBlog.name = 'test blog' objEntry1 = Entry() objEntry1.title = 'Entry one' objEntry2 = Entry() objEntry2.title = 'Entry Two' objBlog.entry_set.add(objEntry1) objBlog.entry_set.add(objEntry2) I get an error which says "null value in column and it violates the foreign key not null constraint". None of my model objects have been saved. Do I have to save the "objBlog" before I could set the entries? I was hoping I could call the save method on objBlog to save it all. NOTE: I am not creating a blog engine and this is just an example.

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• x86 and Memory Addressing

  - by IM

  I've been reading up on memory models in an assembly book I picked up and I have a question or two. Let's say that the address bus has 32 lines, the data bus has 32 lines and the CPU is 32-bit (for simplicity). Now if the CPU makes a read request and sends the 32bit address, but only needs 8 bits, all 32 bits come back anyway? Also, the addresses in memory are still addressed per byte correct? So fetching one byte would bring back 0000 0001 to address 0000 0004? Thanks in advance

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• How do I check for Existence of a Record in GAE

  - by VDev

  I am trying to create a simple view in Django & GAE, which will check if the user has a profile entity and prints a different message for each case. I have the program below, but somehow GAE always seem to return a object. My program is below import datetime from django.http import HttpResponse, HttpResponseRedirect from google.appengine.api import users from google.appengine.ext import db from models import Profile import logging #from accounts.views import profile # Create your views here. def login_view(request): user = users.get_current_user() profile = db.GqlQuery("SELECT * FROM Profile WHERE account = :1", users.get_current_user()) logging.info(profile) logging.info(user) if profile: return HttpResponse("Congratulations Your profile is already created.") else: return HttpResponse("Sorry Your profile is NOT created.") My model object is Profile defined as follows: class Profile(db.Model): first_name = db.StringProperty() last_name = db.StringProperty() gender = db.StringProperty(choices=set(["Male", "Female"])) account = db.UserProperty(required = True) friends = db.ListProperty(item_type=users.User) last_login = db.DateTimeProperty(required=True) Thanks for the help.

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• User HasOne ActiveToken, HasMany Tokens, how to setup in Rails?

  - by viatropos

  I have two simple models: class User < ActiveRecord::Base has_many :tokens # has_one doesn't work, because Token already stores # foreign id to user... # has_one :active_token, :class_name => "Token" # belongs_to doesn't work because Token belongs to # User already, and they both can't belong to each other # belongs_to :active_token, :class_name => "Token" end class Token < ActiveRecord::Base belongs_to :user end I want to say "User has_one :active_token, :class_name => 'Token'", but I can't because Token already belongs_to User. What I did instead was just manually add similar functionality to the user like so: class User < ActiveRecord::Base has_many :tokens attr_accessor :active_token after_create :save_active_token before_destroy :destroy_active_token # it belongs_to, but you can't have both belongs_to each other... def active_token return nil unless self.active_token_id @active_token ||= Token.find(self.active_token_id) end def active_token=(value) self.active_token_id = value.id @active_token = value end def save_active_token self.active_token.user = self self.active_token.save end def destroy_active_token self.active_token.destroy if self.active_token end end Is there a better way?

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• django accessing class variables in a view

  - by dana

  hello, i want to make a notification function, and i need fields from 2 different models. how can i access those fields? in my notification view i wrote this data = Notices.objects.filter(last_login<date_follow) where last_login belongs to the model class User , and date_follow to Follow but it is not a proper and correct way of accessing those variables. How can i access them? I need to compare the two dates for realising the notifications that one did not see since his last login. Thanks!

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• Django & custom auth backend (web service) + no database. How to save stuff in session?

  - by Infinity

  I've been searching here and there, and based on this answer I've put together what you see below. It works, but I need to put some stuff in the user's session, right there inside authenticate. How would I store acme_token in the user's session, so that it will get cleared if they logged out? class AcmeUserBackend(object): # Create a User object if not already in the database? create_unknown_user = False def get_user(self, username): return AcmeUser(id=username) def authenticate(self, username=None, password=None): """ Check the username/password and return an AcmeUser. """ acme_token = ask_another_site_about_creds(username, password) if acme_token: return AcmeUser(id=username) return None ################## from django.contrib.auth.models import User class AcmeUser(User): objects = None # we cannot really use this w/o local DB def save(self): """saving to DB disabled""" pass def get_group_permissions(self): """If you don't make your own permissions module, the default also will use the DB. Throw it away""" return [] # likewise with the other permission defs def get_and_delete_messages(self): """Messages are stored in the DB. Darn!""" return []

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• What is the proper way to check the previous value of a field before saving an object? (Using Django

  - by anonymous coward

  I have a Django Model with updated_by and an approved_by fields, both are ForeignKey fields to the built-in (auth) User models. I am aware that with updated_by, it's easy enough to simply over-ride the .save() method on the Model, and shove the request.user in that field before saving. However, for approved_by, this field should only ever be filled in when a related field (date_approved) is first filled in. I'm somewhat certain that I can check this logically, and fill in the field if the previous value was empty. What is the proper way to check the previous value of a field before saving an object? I do not anticipate that date_approved will ever be changed or updated, nor should there be any reason to ever update the approved_by entry. UPDATE: Regarding forms/validation, I should have mentioned that none of the fields in question are seen by or editable by users of the site. If I have misunderstood, I'm sorry, but I'm not sure how forms and validation apply to my question.

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• how can i introspect properties and model fields in django?

  - by shreddd

  I am trying to get a list of all existing model fields and properties for a given object. Is there a clean way to instrospect an object so that I can get a dict of fields and properties. class MyModel(Model) url = models.TextField() def _get_location(self): return "%s/jobs/%d"%(url, self.id) location = property(_get_location) What I want is something that returns a dict that looks like this: { 'id' : 1, 'url':'http://foo', 'location' : 'http://foo/jobs/1' } I can use model._meta.fields to get the model fields, but this doesn't give me things that are properties but not real DB fields.

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• Dividing web.config into multiple files in asp.net

  - by Jalpesh P. Vadgama

  When you are having different people working on one project remotely you will get some problem with web.config, as everybody was having different version of web.config. So at that time once you check in your web.config with your latest changes the other people have to get latest that web.config and made some specific changes as per their local environment. Most of people who have worked things from remotely has faced that problem. I think most common example would be connection string and app settings changes. For this kind of situation this will be a best solution. We can divide particular section of web.config into the multiple files. For example we could have separate ConnectionStrings.config file for connection strings and AppSettings.config file for app settings file. Most of people does not know that there is attribute called ‘configSource’ where we can  define the path of external config file and it will load that section from that external file. Just like below. <configuration> <appSettings configSource="AppSettings.config"/> <connectionStrings configSource="ConnectionStrings.config"/> </configuration> And you could have your ConnectionStrings.config file like following. <connectionStrings> <add name="DefaultConnection" connectionString="Data Source=(LocalDb)\v11.0;Initial Catalog=aspnet-WebApplication1-20120523114732;Integrated Security=True" providerName="System.Data.SqlClient" /> </connectionStrings> Same way you have another AppSettings.Config file like following. <appSettings> <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true" /> <add key="ValidationSettings:UnobtrusiveValidationMode" value="WebForms" /> </appSettings> That's it. Hope you like this post. Stay tuned for more..

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• SQL Developer Database Diff – Compare Objects From Multiple Schemas

  - by thatjeffsmith

  Ever wonder why Database Diff isn’t called Schema Diff? One reason is because SQL Developer allows you select objects from more than one schema in the ‘Source’ connection for the compare. Simply use the ‘More’ dialog view and select as many tables from as many different schemas as you require Now, before you get around to testing this – as you should never believe what I say, trust but verify – two things you need to know: I’m using SQL Developer version 3.2 On the initial screen you need to use the ‘Maintain’ option Maintain tells SQL Developer to use the schema designation in the source connection to find the same corresponding object in the destination schema. Choose ‘maintain’ if you want to compare objects in the same schema in the destination but don’t have the user login for that schema. So after you’ve selected your databases, your diff preferences, and your objects – you’re ready to perform the compare and review your results. The DIFF Report Notice the highlighted text, SQL Developer is ‘maintaining’ the Schema context from the two databases. Short and sweet. That’s pretty much all there is to doing a compare with SQL Developer with multiple schemas involved. You may have noticed in some posts lately that my editor screenshots had a ‘green screen’ look and feel to them. What’s with the black background in your editors? In the SQL Developer preferences, you can set your editor color schemes. I started with the ‘Twilight’ scheme (team Jacob in case you’re wondering) and then customized it further by going with a default green font color. You could go pretty crazy in here, and I’m assuming 90% of you could care less and will just stick with the original. But for those of you who are particular about your IDE styling – go crazy! SQL Developer Editor Display Preferences

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• Running Multiple Queries in Oracle SQL Developer

  - by thatjeffsmith

  There are two methods for running queries in SQL Developer: Run Statement Run Statement, Shift+Enter, F9, or this button Run Script No grids, just script (SQL*Plus like) ouput is fine, thank you very much! What’s the Difference? There are some obvious differences between the two features, the most obvious being the format of the output delivered. But there are some other, more subtle differences here, primarily around fetching. What is Fetch? After you run send your query to Oracle, it has to do 3 things: Parse Execute Fetch Technically it has to do at least 2 things, and sometimes only 1. But, to get the data back to the user, the fetch must occur. If you have a 10 row query or a 1,000,000 row query, this can mean 1 or many fetches in groups of records. Ok, before I went on the Fetch tangent, I said there were two ways to run statements in SQL Developer: Run Statement Run statement brings your query results to a grid with a single fetch. The user sees 50, 100, 500, etc rows come back, but SQL Developer and the database know that there are more rows waiting to be retrieved. The process on the server that was used to execute the query is still hanging around too. To alleviate this, increase your fetch size to 500. Every query ran will come back with the first 500 rows, and rows will be continued to be fetched in 500 row increments. You’ll then see most of your ad hoc queries complete with a single fetch. Scroll down, or hit Ctrl+End to force a full fetch and get all your rows back. Run Script Run Script runs the contents of the worksheet (or what’s highlighted) as a ‘script.’ What does that mean exactly? Think of this as being equivalent to running this in SQL*Plus: @my_script.sql; Each statement is executed. Also, ALL rows are fetched. So once it’s finished executing, there are no open cursors left around. The more obvious difference here is that the output comes back formatted as plain old text. Run one or more commands plus SQL*Plus commands like SET and SPOOL The Trick: Run Statement Works With Multiple Statements! It says ‘run statement,’ but if you select more than one with your mouse and hit the button – it will run each and throw the results to 1 grid for each statement. If you mouse hover over the Query Result panel tab, SQL Developer will tell you the query used to populate that grid. This will work regardless of what you have this preference set to: DATABASE – WORKSHEET – SHOW QUERY RESULTS IN NEW TABS Mind the fetch though! Close those cursors by bring back all the records or closing the grids when you’re done with them.

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• Draw multiple objects with textures

  - by Simplex

  I want to draw cubes using textures. void OperateWithMainMatrix(ESContext* esContext, GLfloat offsetX, GLfloat offsetY, GLfloat offsetZ) { UserData *userData = (UserData*) esContext->userData; ESMatrix modelview; ESMatrix perspective; //Manipulation with matrix ... glVertexAttribPointer(userData->positionLoc, 3, GL_FLOAT, GL_FALSE, 0, cubeFaces); //in cubeFaces coordinates verticles cube glVertexAttribPointer(userData->normalLoc, 3, GL_FLOAT, GL_FALSE, 0, cubeFaces); //for normals (use in fragment shaider for textures) glEnableVertexAttribArray(userData->positionLoc); glEnableVertexAttribArray(userData->normalLoc); // Load the MVP matrix glUniformMatrix4fv(userData->mvpLoc, 1, GL_FALSE, (GLfloat*)&userData->mvpMatrix.m[0][0]); //Bind base map glActiveTexture(GL_TEXTURE0); glBindTexture(GL_TEXTURE_CUBE_MAP, userData->baseMapTexId); //Set the base map sampler to texture unit to 0 glUniform1i(userData->baseMapLoc, 0); // Draw the cube glDrawArrays(GL_TRIANGLES, 0, 36); } (coordinates transformation is in OperateWithMainMatrix() ) Then Draw() function is called: void Draw(ESContext *esContext) { UserData *userData = esContext->userData; // Set the viewport glViewport(0, 0, esContext->width, esContext->height); // Clear the color buffer glClear(GL_COLOR_BUFFER_BIT); // Use the program object glUseProgram(userData->programObject); OperateWithMainMatrix(esContext, 0.0f, 0.0f, 0.0f); eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface); } This work fine, but if I try to draw multiple cubes (next code for example): void Draw(ESContext *esContext) { ... // Use the program object glUseProgram(userData->programObject); OperateWithMainMatrix(esContext, 2.0f, 0.0f, 0.0f); OperateWithMainMatrix(esContext, 1.0f, 0.0f, 0.0f); OperateWithMainMatrix(esContext, 0.0f, 0.0f, 0.0f); OperateWithMainMatrix(esContext, -1.0f, 0.0f, 0.0f); OperateWithMainMatrix(esContext, -2.0f, 0.0f, 0.0f); eglSwapBuffers(esContext->eglDisplay, esContext->eglSurface); } A side faces overlapes frontal face. The side face of the right cube overlaps frontal face of the center cube. How can i remove this effect and display miltiple cubes without it?

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• Drawing multiple objects from one Vertex Buffer Object in OpenGL/OpenTK

  - by stoney78us

  I am trying to experimenting drawing method using VBO in OpenGL. Many people normally use 1 vbo to store one object data array. I was trying to do something quite opposite which is storing multiple object data into 1 vbo then drawing it. There is story behind why i want to do this. I want to group many of objects as a single object sometime. However my code doesn't do the justice. Following is my pseudo code: //Data double[] vertices = {line strip 1, line strip 2, line strip 3}; //series of vertices int linestrip1offset = index of the first vertex in line strip 1; int linestrip2offset = index of the first vertex in line strip 2; int linestrip3offset = index of the first vertex in line strip 3; int linestrip1VertexNum = number of vertices in linestrip 1; int linestrip2VertexNum = number of vertices in linestrip 2; int linestrip3VertexNum = number of vertices in linestrip 3; //Setting Up void init() { int[] vBO = new int[1]; GL.GenBuffer(1, vBO); GL.BindBuffer(BufferTarget.ArrayBuffer, vBO[0]); GL.BufferData(BufferTarget.ArrayBuffer, new IntPtr(_vertices.Length * sizeof(double)), _vertices, BufferUsageHint.StaticDraw); GL.EnableClientState(Array.VertexArray); } //Drawing void draw() { GL.BindBuffer(BufferTarget.ArrayBuffer, vBO[0]); GL.EnableClientState(ArrayCap.VertexArray); GL.VertexPointer(3, VertexPointerType.Double, 0, linestrip1offset); //drawing first linestrip GL.DrawArrays(drawMode, linestrip1offset , linestrip1VertexNum ); GL.VertexPointer(3, VertexPointerType.Double, 0, linestrip2offset); //drawing second linestrip GL.DrawArrays(drawMode, linestrip2offset , linestrip2VertexNum ); GL.VertexPointer(3, VertexPointerType.Double, 0, linestrip3offset); //drawing third linestrip GL.DrawArrays(drawMode, linestrip3offset , linestrip3VertexNum ); GL.DisableClientState(ArrayCap.VertexArray); GL.BindBuffer(BufferTarget.ArrayBuffer, 0); } I don't know what i did wrong but i think technically it should work where we can tell OpenGL which part of the data in the vBO to be drawn.

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• How to send multiple MVP matrices to a vertex shader in OpenGL ES 2.0

  - by Carbon Crystal

  I'm working my way through optimizing the rendering of sprites in a 2D game using OpenGL ES and I've hit the limit of my knowledge when it comes to GLSL and vertex shaders. I have two large float buffers containing my vertex coordinates and texture coordinates (eventually this will be one buffer) for multiple sprites in order to perform a single glDrawArrays call. This works but I've hit a snag when it comes to passing the transformation matrix into the vertex shader. My shader code is: uniform mat4 u_MVPMatrix; attribute vec4 a_Position; attribute vec2 a_TexCoordinate; varying vec2 v_TexCoordinate; void main() { v_TexCoordinate = a_TexCoordinate; gl_Position = u_MVPMatrix * a_Position; } In Java (Android) I am using a FloatBuffer to store the vertex/texture data and this is provided to the shader like so: mGlEs20.glVertexAttribPointer(mVertexHandle, Globals.GL_POSITION_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mVertexCoordinates); mGlEs20.glVertexAttribPointer(mTextureCoordinateHandle, Globals.GL_TEXTURE_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mTextureCoordinates); (The Globals.GL_POSITION_VERTEX_COUNT etc are just integers with the value of 2 right now) And I'm passing the MVP (Model/View/Projection) matrix buffer like this: GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mModelCoordinates); (mModelCoordinates is a FloatBuffer containing 16-float sequences representing the MVP matrix for each sprite) This renders my scene but all the sprites share the same transformation, so it's obviously only picking the first 16 elements from the buffer which makes sense since I am passing in "1" as the second parameter. The documentation for this method says: "This should be 1 if the targeted uniform variable is not an array of matrices, and 1 or more if it is an array of matrices." So I tried modifying the shader with a fixed size array large enough to accomodate most of my scenarios: uniform mat4 u_MVPMatrix[1000]; But this lead to an error in the shader: cannot convert from 'uniform array of 4X4 matrix of float' to 'Position 4-component vector of float' This just seems wrong anyway as it's not clear to me how the shader would know when to transition to the next matrix anyway. Anyone have an idea how I can get my shader to pick up a different MVP matrix (i.e. the NEXT 16 floats) from my MVP buffer for every 4 vertices it encounters? (I am using GL_TRIANGLE_STRIP so each sprite has 4 vertices). Thanks!

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• Efficient way to find unique elements in a vector compared against multiple vectors

  - by SyncMaster

  I am trying find the number of unique elements in a vector compared against multiple vectors using C++. Suppose I have, v1: 5, 8, 13, 16, 20 v2: 2, 4, 6, 8 v3: 20 v4: 1, 2, 3, 4, 5, 6, 7 v5: 1, 3, 5, 7, 11, 13, 15 The number of unique elements in v1 is 1 (i.e. number 16). I tried two approaches. Added vectors v2,v3,v4 and v5 into a vector of vector. For each element in v1, checked if the element is present in any of the other vectors. Combined all the vectors v2,v3,v4 and v5 using merge sort into a single vector and compared it against v1 to find the unique elements. Note: sample_vector = v1 and all_vectors_merged contains v2,v3,v4,v5 //Method 1 unsigned int compute_unique_elements_1(vector<unsigned int> sample_vector,vector<vector<unsigned int> > all_vectors_merged) { unsigned int duplicate = 0; for (unsigned int i = 0; i < sample_vector.size(); i++) { for (unsigned int j = 0; j < all_vectors_merged.size(); j++) { if (std::find(all_vectors_merged.at(j).begin(), all_vectors_merged.at(j).end(), sample_vector.at(i)) != all_vectors_merged.at(j).end()) { duplicate++; } } } return sample_vector.size()-duplicate; } // Method 2 unsigned int compute_unique_elements_2(vector<unsigned int> sample_vector, vector<unsigned int> all_vectors_merged) { unsigned int unique = 0; unsigned int i = 0, j = 0; while (i < sample_vector.size() && j < all_vectors_merged.size()) { if (sample_vector.at(i) > all_vectors_merged.at(j)) { j++; } else if (sample_vector.at(i) < all_vectors_merged.at(j)) { i++; unique ++; } else { i++; j++; } } if (i < sample_vector.size()) { unique += sample_vector.size() - i; } return unique; } Of these two techniques, I see that Method 2 gives faster results. 1) Method 1: Is there a more efficient way to find the elements than running std::find on all the vectors for all the elements in v1. 2) Method 2: Extra overhead in comparing vectors v2,v3,v4,v5 and sorting them. How can I do this in a better way?

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• MVVM pattern and nested view models - communication and lookup lists

  - by LostInWPF

  I am using Prism for a new application that I am creating. There are several lookup lists that will be used in several places in the application. Therefore it makes sense to define it once and use that everywhere I need that functionality. My current solution is to use typed data templates to render the controls inside a content control. <DataTemplate DataType={x:Type ListOfCountriesViewModel}> <ComboBox ItemsSource={Binding Countries} SelectedItem="{Binding SelectedCountry"/> </DataTemplate> <DataTemplate DataType={x:Type ListOfRegionsViewModel}> <ComboBox ItemsSource={Binding Countries} SelectedItem={Binding SelectedRegion} /> </DataTemplate> public class ParentViewModel { SelectedCountry get; set; SelectedRegion get; set; ListOfCountriesViewModel CountriesVM; ListOfRegionsViewModel RgnsVM; } Then in my window I have 2 content controls and the rest of the controls <ContentControl Content="{Binding CountriesVM}"></ContentControl> <ContentControl Content="{Binding RgnsVM}"></ContentControl> <Rest of controls on view> At the moment I have this working and the SelectedItems for the combo boxes are publising events via EventAggregator from the child view models which are then subscribed to in the parent view model. I am not sure that this is the best way to go as I can imagine I would end up with a lot of events very quickly and it will become unwieldy. Also if I was to use the same view model on another window it will publish the event and this parent viewmodel is subscribed to it which could have unintended consequences. My questions are :- Is this the best way to put lookup lists in a view which can be re-used across screens? How do I make it so that the combobox which is bound to the child viewmodel sets the relevant property on the parent viewmodel without using events / mediator. e.g in this case SelectedCountry for example? Any alternative implementation proposals for what I am trying to do? I have a feeling I am missing something obvious and there is so much info it is hard to know what is right so any help would be most gratefully received.

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• How to arrange models, views, controllers in a Kohana 3 project

  - by Pekka

  I'm looking at how to set up a mid-sized web application with Kohana 3. I have implemented MVC patterns in the past but never worked against a "formalized" MVC framework so I'm still getting my head around the terminology - toying around with basic examples, building views and templates, and so on. I'm progressing fairly well but I want to set up a real-world web project (one of my own that I've been planning for quite some time now) as a learning object. I learn best by example, but example-based documentation is a bit sparse for Kohana 3 right now - they say so themselves on the site. While I'm not worried about getting into the framework soon enough, I'm a bit concerned about arranging a healthily structured code base from the start - i.e. how to split up controllers, how to name them, and how to separate the functionality into the appropriate models. My application could, in its core, be described as a business directory with a main businesses table. Businesses can be listed by category and by street name. Each business has a detail page. Business owners can log in and edit their business's entry. Businesses can post offers into an offers table. I know this is not very detailed, but I don't want to cram too much information into this question. I'll be more than happy to go into more detail if needed. Supposing I have all the basic functionality worked out and in place already - list all businesses, edit business, list businesses by street name, create offer logged in as business, and so on, and I'm just looking for how to fit the functionality into a MVC pattern and into a Kohana application structure that can be easily extended: Do you know real-life, publicly accessible examples of "database-heavy" applications like directories, online communities... with a log-in area built on Kohana 3 where I could take a peek how they do it? Are there conventions or best practices on how to structure an extendable login area for end users in a Kohana project that is not only able to handle a business directory page, but further products on separate pages as well? Do you know application structuring HOWTOs or best practices for Kohana 3 not mentioned in the user guide and the inofficial Wiki? Have you built something similar and could give me some recommendations?

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• Arranging models, views, controllers in a Kohana 3 project

  - by Pekka

  I'm looking at how to set up a mid-sized web application with Kohana 3. I have implemented MVC patterns in the past but never worked against a "formalized" MVC framework so I'm still getting my head around the terminology - toying around with basic examples, building views and templates, and so on. I'm progressing fairly well but I want to set up a real-world web project (one of my own that I've been planning for quite some time now) as a learning object. I learn best by example, but example-based documentation is a bit sparse for Kohana 3 right now - they say so themselves on the site. While I'm not worried about getting into the framework soon enough, I'm a bit concerned about arranging a healthily structured code base from the start - i.e. how to split up controllers, how to name them, and how to separate the functionality into the appropriate models. My application could, in its core, be described as a business directory with a main businesses table. Businesses can be listed by category and by street name. Each business has a detail page. Business owners can log in and edit their business's entry. Businesses can post offers into an offers table. I know this is pretty vague, but I don't want to cram too much information into this question. I'll be more than happy to go into more detail if needed. Supposing I have all the basic functionality worked out and in place already - list all businesses, edit business, list businesses by street name, create offer, and so on, and I'm just looking for how to fit the functionality into a MVC pattern and into a Kohana application structure that can be easily extended: Do you know real-life, publicly accessible examples of "database-heavy" applications like directories, online communities... with a log-in area built on Kohana 3 where I could take a peek how they do it? Are there conventions or best practices on how to structure an extendable login area for end users in a Kohana project that is not only able to handle a business directory page, but further products on separate pages as well? Do you know application structuring HOWTOs or best practices for Kohana 3 not mentioned in the user guide and the inofficial Wiki? Have you built something similar and could give me some recommendations?

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• Non-linear regression models in PostgreSQL using R

  - by Dave Jarvis

  Background I have climate data (temperature, precipitation, snow depth) for all of Canada between 1900 and 2009. I have written a basic website and the simplest page allows users to choose category and city. They then get back a very simple report (without the parameters and calculations section): The primary purpose of the web application is to provide a simple user interface so that the general public can explore the data in meaningful ways. (A list of numbers is not meaningful to the general public, nor is a website that provides too many inputs.) The secondary purpose of the application is to provide climatologists and other scientists with deeper ways to view the data. (Using too many inputs, of course.) Tool Set The database is PostgreSQL with R (mostly) installed. The reports are written using iReport and generated using JasperReports. Poor Model Choice Currently, a linear regression model is applied against annual averages of daily data. The linear regression model is calculated within a PostgreSQL function as follows: SELECT regr_slope( amount, year_taken ), regr_intercept( amount, year_taken ), corr( amount, year_taken ) FROM temp_regression INTO STRICT slope, intercept, correlation; The results are returned to JasperReports using: SELECT year_taken, amount, year_taken * slope + intercept, slope, intercept, correlation, total_measurements INTO result; JasperReports calls into PostgreSQL using the following parameterized analysis function: SELECT year_taken, amount, measurements, regression_line, slope, intercept, correlation, total_measurements, execute_time FROM climate.analysis( $P{CityId}, $P{Elevation1}, $P{Elevation2}, $P{Radius}, $P{CategoryId}, $P{Year1}, $P{Year2} ) ORDER BY year_taken This is not an optimal solution because it gives the false impression that the climate is changing at a slow, but steady rate. Questions Using functions that take two parameters (e.g., year [X] and amount [Y]), such as PostgreSQL's regr_slope: What is a better regression model to apply? What CPAN-R packages provide such models? (Installable, ideally, using apt-get.) How can the R functions be called within a PostgreSQL function? If no such functions exist: What parameters should I try to obtain for functions that will produce the desired fit? How would you recommend showing the best fit curve? Keep in mind that this is a web app for use by the general public. If the only way to analyse the data is from an R shell, then the purpose has been defeated. (I know this is not the case for most R functions I have looked at so far.) Thank you!

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• Django database caching

  - by hekevintran

  The object user has a foreign key relationship to address. Is there a difference between samples 1 and 2? Does sample 1 run the query multiple times? Or is the address object cached? # Sample 1 country = user.address.country city = user.address.city state = user.address.state # Sample 2 address = user.address country = address.country city = address.city state = address.state

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• Multiprogramming in Django, writing to the Database

  - by Marcus Whybrow

  Introduction I have the following code which checks to see if a similar model exists in the database, and if it does not it creates the new model: class BookProfile(): # ... def save(self, *args, **kwargs): uniqueConstraint = {'book_instance': self.book_instance, 'collection': self.collection} # Test for other objects with identical values profiles = BookProfile.objects.filter(Q(**uniqueConstraint) & ~Q(pk=self.pk)) # If none are found create the object, else fail. if len(profiles) == 0: super(BookProfile, self).save(*args, **kwargs) else: raise ValidationError('A Book Profile for that book instance in that collection already exists') I first build my constraints, then search for a model with those values which I am enforcing must be unique Q(**uniqueConstraint). In addition I ensure that if the save method is updating and not inserting, that we do not find this object when looking for other similar objects ~Q(pk=self.pk). I should mention that I ham implementing soft delete (with a modified objects manager which only shows non-deleted objects) which is why I must check for myself rather then relying on unique_together errors. Problem Right thats the introduction out of the way. My problem is that when multiple identical objects are saved in quick (or as near as simultaneous) succession, sometimes both get added even though the first being added should prevent the second. I have tested the code in the shell and it succeeds every time I run it. Thus my assumption is if say we have two objects being added Object A and Object B. Object A runs its check upon save() being called. Then the process saving Object B gets some time on the processor. Object B runs that same test, but Object A has not yet been added so Object B is added to the database. Then Object A regains control of the processor, and has allready run its test, even though identical Object B is in the database, it adds it regardless. My Thoughts The reason I fear multiprogramming could be involved is that each Object A and Object is being added through an API save view, so a request to the view is made for each save, thus not a single request with multiple sequential saves on objects. It might be the case that Apache is creating a process for each request, and thus causing the problems I think I am seeing. As you would expect, the problem only occurs sometimes, which is characteristic of multiprogramming or multiprocessing errors. If this is the case, is there a way to make the test and set parts of the save() method a critical section, so that a process switch cannot happen between the test and the set?

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