Tutorial by Examples: r

When trying to select from a table called order like this select * from order the error rises: Error Code: 1064. You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'order' at line 1 Reserved keywords in MySQ...

Lambda expressions can be used to handle events, which is useful when: The handler is short. The handler never needs to be unsubscribed. A good situation in which a lambda event handler might be used is given below: smtpClient.SendCompleted += (sender, args) => Console.WriteLine("Ema...

public interface IShape { decimal Area(); } public struct Rectangle : IShape { public decimal Length { get; set; } public decimal Width { get; set; } public decimal Area() { return Length * Width; } }

Find properties with a custom attribute - MyAttribute var props = t.GetProperties(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance).Where( prop => Attribute.IsDefined(prop, typeof(MyAttribute))); Find all custom attributes on a given property va...

The android:process field defines the name of the process where the service is to run. Normally, all components of an application run in the default process created for the application. However, a component can override the default with its own process attribute, allowing you to spread your applicat...

Given the model: class MyModel(models.Model): name = models.CharField(max_length=10) model_num = models.IntegerField() flag = models.NullBooleanField(default=False) We can use Q objects to create AND , OR conditions in your lookup query. For example, say we want all objects that ...

SELECT FIND_IN_SET('b','a,b,c'); Return value: 2 SELECT FIND_IN_SET('d','a,b,c'); Return value: 0

Django manger is an interface through which the django model queries the database. The objects field used in most django queries is actually the default manager created for us by django (this is only created if we don't define custom managers). Why would we define a custom manager/queryset? To avo...

tl;dr : Create a base class that defines two user objects (say user and another_user). Create your other models and define three Client instances. self.client : Representing user logged in browser self.another_client : Representing another_user 's client self.unlogged_client : Representing unlo...

Filters are a special type of function that can modify how something is printed out to the page, or can be used to filter an array, or a ng-repeat action. You can create a filter by calling the app.filter() method, passing it a name and a function. See the examples below for details on syntax. Fo...

To run a container interactively, pass in the -it options: $ docker run -it ubuntu:14.04 bash root@8ef2356d919a:/# echo hi hi root@8ef2356d919a:/# -i keeps STDIN open, while -t allocates a pseudo-TTY.

package main import ( "log" "text/template" "os" ) type Person struct{ MyName string MyAge int } var myTempContents string= ` This person's name is : {{.MyName}} And he is {{.MyAge}} years old. ` func main() { t,err := temp...

To assign variables from the command-line, -v can be used: $ awk -v myvar="hello" 'BEGIN {print myvar}' hello Note that there are no spaces around the equal sign. This allows to use shell variables: $ shell_var="hello" $ awk -v myvar="$shell_var" 'BEGIN {print m...

Node Version Manager, otherwise known as nvm, is a bash script that simplifies the management of multiple Node.js versions. To install nvm, use the provided install script: $ curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.31.3/install.sh | bash For windows there is a nvm-windows p...

Rcpp Attributes makes the process of working with R and C++ straightforward. The form of attributes take: // [[Rcpp::attribute]] The use of attributes is typically associated with: // [[Rcpp::export]] that is placed directly above a declared function header when reading in a C++ file via sou...

Within C++, one can set different compilation flags using: // [[Rcpp::plugins(name)]] List of the built-in plugins: // built-in C++11 plugin // [[Rcpp::plugins(cpp11)]] // built-in C++11 plugin for older g++ compiler // [[Rcpp::plugins(cpp0x)]] // built-in C++14 plugin for C++14 standa...

In some cases you may want to wrap a synchronous operation inside a promise to prevent repetition in code branches. Take this example: if (result) { // if we already have a result processResult(result); // process it } else { fetchResult().then(processResult); } The synchronous and async...

Similarly to the SimpleXML, you can use DOMDocument to parse XML from a string or from a XML file 1. From a string $doc = new DOMDocument(); $doc->loadXML($string); 2. From a file $doc = new DOMDocument(); $doc->load('books.xml');// use the actual file path. Absolute or relative Exa...

When you want to use user generated content in the SQL, it with done with parameters. For example for searching user with the name aminadav you should do: var username = 'aminadav'; var querystring = 'SELECT name, email from users where name = ?'; connection.query(querystring, [username], functi...

You send the query as a string and in response callback with the answer is received. The callback gives you error, array of rows and fields. Each row contains all the column of the returned table. Here is a snippet for the following explanation. connection.query('SELECT name,email from users', fu...