Tutorial by Examples: r

NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:@"value1", @"key1", @"value2", @"key2", nil]; or NSArray *keys = [NSArray arrayWithObjects:@"key1", @"key2", nil]; NSArray *objects = [NSArray arrayWithObjects:@"va...

Prefer public class Order { public OrderLine AddOrderLine(OrderLine orderLine) { if (orderLine == null) throw new ArgumentNullException(nameof(orderLine)); ... } } Over public class Order { public OrderLine AddOrderLine(OrderLine orderLine) { ...

What is Ubuntu Ubuntu is an open source software platform, but colloquially, when Ubuntu is referred to it's mainly toward the Ubuntu operating system. Ubuntu is based on Debian and uses the same package management system (deb and apt). Installation So you want to give Ubuntu a try! That's gr...

You may need to convert a Stream emitting Optional to a Stream of values, emitting only values from existing Optional. (ie: without null value and not dealing with Optional.empty()). Optional<String> op1 = Optional.empty(); Optional<String> op2 = Optional.of("Hello World");...

The function php_sapi_name() and the constant PHP_SAPI both return the type of interface (Server API) that is being used by PHP. They can be used to restrict the execution of a script to the command line, by checking whether the output of the function is equal to cli. if (php_sapi_name() === 'cli')...

A data.table is an enhanced version of the data.frame class from base R. As such, its class() attribute is the vector "data.table" "data.frame" and functions that work on a data.frame will also work with a data.table. There are many ways to create, load or coerce to a data.table....

A class marked with the keyword abstract cannot be instantiated. A class must be marked as abstract if it contains abstract members or if it inherits abstract members that it doesn't implement. A class may be marked as abstract even if no abstract members are involved. Abstract classes are usually...

Partial templates (partials) are a way of breaking the rendering process into more manageable chunks. Partials allow you to extract pieces of code from your templates to separate files and also reuse them throughout your templates. To create a partial, create a new file that begins with an undersco...

To let rails automatically and correctly link assets (css/js/images) in most cases you want to use built in helpers. (Official documentation) Image helpers image_path This returns the path to an image asset in app/assets/images. image_path("edit.png") # => /assets/edit.png image_...

Add/remove fields in existing tables Create a migration by running: rails generate migration AddTitleToCategories title:string This will create a migration that adds a title column to a categories table: class AddTitleToCategories < ActiveRecord::Migration[5.0] def change add_column...

preg_match checks whether a string matches the regular expression. $string = 'This is a string which contains numbers: 12345'; $isMatched = preg_match('%^[a-zA-Z]+: [0-9]+$%', $string); var_dump($isMatched); // bool(true) If you pass in a third parameter, it will be populated with the matchi...

NSString has a length property to get the number of characters. NSString *string = @"example"; NSUInteger length = string.length; // length equals 7 As in the Splitting Example, keep in mind that NSString uses UTF-16 to represent characters. The length is actually just the numbe...

This is the Python 2 syntax, note the commas , on the raise and except lines: Python 2.x2.3 try: raise IOError, "input/output error" except IOError, exc: print exc In Python 3, the , syntax is dropped and replaced by parenthesis and the as keyword: try: raise IOErro...

Rails uses sqlite3 as the default database, but you can generate a new rails application with a database of your choice. Just add the -d option followed by the name of the database. $ rails new MyApp -T -d postgresql This is a (non-exhaustive) list of available database options: mysql oracle...

Suppose you have a repository structure like this: examples/ output.log src/ <files not shown> output.log README.md output.log in the examples directory is valid and required for the project to gather an understanding while the one beneath src/ is created while debugging a...

interface IFoo { } class Foo : IFoo { } class Bar : IFoo { } var item0 = new Foo(); var item1 = new Foo(); var item2 = new Bar(); var item3 = new Bar(); var collection = new IFoo[] { item0, item1, item2, item3 }; Using OfType var foos = collection.OfType<Foo>(); // result: IEnum...

Special care needs to be taken when there is a possibility that an array become an empty array when it comes to logical operators. It is often expected that if all(A) is true then any(A) must be true and if any(A) is false, all(A) must also be false. That is not the case in MATLAB with empty arrays....

Strings are compared for equality using isEqualToString: The == operator just tests for object identity and does not compare the logical values of objects, so it can't be used: NSString *stringOne = @"example"; NSString *stringTwo = [stringOne mutableCopy]; BOOL objectsAreIdentical =...

Modules can have a special variable named __all__ to restrict what variables are imported when using from mymodule import *. Given the following module: # mymodule.py __all__ = ['imported_by_star'] imported_by_star = 42 not_imported_by_star = 21 Only imported_by_star is imported when usi...

The checked out file will overwrite not yet commited changes you did in this file. This command will check out the file file.example (which is located in the directory path/to/) and overwrite any changes you might have made to this file. git checkout some-branch path/to/file some-branch can be ...