Tutorial by Examples: r

WITH RECURSIVE ManagersOfJonathon AS ( -- start with this row SELECT * FROM Employees WHERE ID = 4 UNION ALL -- get manager(s) of all previously selected rows SELECT Employees.* FROM Employees JOIN ManagersOfJonathon ON Employees.ID = Manager...

Most databases do not have a native way of generating a series of numbers for ad-hoc use; however, common table expressions can be used with recursion to emulate that type of function. The following example generates a common table expression called Numbers with a column i which has a row for numbe...

WITH RECURSIVE ManagedByJames(Level, ID, FName, LName) AS ( -- start with this row SELECT 1, ID, FName, LName FROM Employees WHERE ID = 1 UNION ALL -- get employees that have any of the previously selected rows as manager SELECT ManagedByJames.Level + 1, ...

BuildConfigField Gradle allows buildConfigField lines to define constants. These constants will be accessible at runtime as static fields of the BuildConfig class. This can be used to create flavors by defining all fields within the defaultConfig block, then overriding them for individual build fla...

# Create the nodes # In a real world scenario we would use at least 3 managers to cover the fail of one manager. docker-machine create -d virtualbox manager docker-machine create -d virtualbox worker1 # Create the swarm # It is possible to define a port for the *advertise-addr* and *listen-ad...

MATLAB supports (and encourages) vectorized operations on vectors and matrices. For example, suppose we have A and B, two n-by-m matrices and we want C to be the element-wise product of the corresponding elements (i.e., C(i,j) = A(i,j)*B(i,j)). The un-vectorized way, using nested loops is as follo...

public struct Vector { public int X; public int Y; public int Z; } public struct Point { public decimal x, y; public Point(decimal pointX, decimal pointY) { x = pointX; y = pointY; } } struct instance fields can be set via a p...

Assuming the following Person class: public class Person { public string Name { get; set; } public int Age { get; set; } } The following lambda: p => p.Age > 18 Can be passed as an argument to both methods: public void AsFunc(Func<Person, bool> func) public void AsE...

You can combine object initializers with constructors to initialize types if necessary. Take for example a class defined as such: public class Book { public string Title { get; set; } public string Author { get; set; } public Book(int id) { //do things } // the...

<input type="reset" value="Reset"> An input of type reset creates a button which, when clicked, resets all inputs in the form it is contained in to their default state. Text in an input field will be reset to blank or its default value (specified using the value attri...

length counts the occurences of elements a in a foldable structure t a. ghci> length [7, 2, 9] -- t ~ [] 3 ghci> length (Right 'a') -- t ~ Either e 1 -- 'Either e a' may contain zero or one 'a' ghci> length (Left "foo") -- t ~ Either String 0 ghci> length (3, True) ...

Any fold can be run in the opposite direction with the help of the Dual monoid, which flips an existing monoid so that aggregation goes backwards. newtype Dual a = Dual { getDual :: a } instance Monoid m => Monoid (Dual m) where mempty = Dual mempty (Dual x) `mappend` (Dual y) = Dua...

To instantiate Foldable you need to provide a definition for at least foldMap or foldr. data Tree a = Leaf | Node (Tree a) a (Tree a) instance Foldable Tree where foldMap f Leaf = mempty foldMap f (Node l x r) = foldMap f l `mappend` f x `mappend` foldMap f r fo...

The function strtok breaks a string into a smaller strings, or tokens, using a set of delimiters. #include <stdio.h> #include <string.h> int main(void) { int toknum = 0; char src[] = "Hello,, world!"; const char delimiters[] = ", !"; char *to...

import Data.Traversable as Traversable data MyType a = -- ... instance Traversable MyType where traverse = -- ... Every Traversable structure can be made a Foldable Functor using the fmapDefault and foldMapDefault functions found in Data.Traversable. instance Functor MyType where ...

Implementations of traverse usually look like an implementation of fmap lifted into an Applicative context. data Tree a = Leaf | Node (Tree a) a (Tree a) instance Traversable Tree where traverse f Leaf = pure Leaf traverse f (Node l x r) = Node <$> traverse f l <*...

A traversal can be run in the opposite direction with the help of the Backwards applicative functor, which flips an existing applicative so that composed effects take place in reversed order. newtype Backwards f a = Backwards { forwards :: f a } instance Applicative f => Applicative (Backward...

The standard (section 23.3.7) specifies that a specialization of vector<bool> is provided, which optimizes space by packing the bool values, so that each takes up only one bit. Since bits aren't addressable in C++, this means that several requirements on vector are not placed on vector<bool...

When the following is compiled, it will return a different value depending on which directives are defined. // Compile with /d:A or /d:B to see the difference string SomeFunction() { #if A return "A"; #elif B return "B"; #else return "C"; #endif ...

Compiler warnings can be generated using the #warning directive, and errors can likewise be generated using the #error directive. #if SOME_SYMBOL #error This is a compiler Error. #elif SOME_OTHER_SYMBOL #warning This is a compiler Warning. #endif