Tutorial by Examples: u

You can iterate on the object returned by groupby(). The iterator contains (Category, DataFrame) tuples. # Same example data as in the previous example. import numpy as np import pandas as pd np.random.seed(0) df = pd.DataFrame({'Age': np.random.randint(20, 70, 100), 'Sex':...

Consider the utility class pattern: a class with only static methods and no fields. It's recommended to prevent instantiation of such classes by adding a private a constructor. This live template example makes it easy to add a private constructor to an existing class, using the name of the enclos...

Imagine a goroutine with a two step process, where the main thread needs to do some work between each step: func main() { ch := make(chan struct{}) go func() { // Wait for main thread's signal to begin step one <-ch // Perform work time.Sle...

main.go: package main import ( "fmt" "io/ioutil" "log" "net/http" ) func fetchContent(url string) (string, error) { res, err := http.Get(url) if err != nil { return "", nil } defer res.Body.Clo...

Unlike a named class or struct, unnamed classes and structs must be instantiated where they are defined, and cannot have constructors or destructors. struct { int foo; double bar; } foobar; foobar.foo = 5; foobar.bar = 4.0; class { int baz; public: int buzz; ...

As a non-standard extension to C++, common compilers allow the use of classes as anonymous members. struct Example { struct { int inner_b; }; int outer_b; //The anonymous struct's members are accessed as if members of the parent struct Example() : inner...

By default, the implicit operator() of a lambda is const. This disallows performing non-const operations on the lambda. In order to allow modifying members, a lambda may be marked mutable, which makes the implicit operator() non-const: int a = 0; auto bad_counter = [a] { return a++; // er...

This example shows a simple image cropping function that takes an image and cropping coordinates and returns the cropped image. function cropImage(image, croppingCoords) { var cc = croppingCoords; var workCan = document.createElement("canvas"); // create a canvas workCan.wi...

f = fn {:a, :b} -> IO.puts "Tuple {:a, :b}" [] -> IO.puts "Empty list" end f.({:a, :b}) # Tuple {:a, :b} f.([]) # Empty list

{ a, b, c } = { "Hello", "World", "!" } IO.puts a # Hello IO.puts b # World IO.puts c # ! # Tuples of different size won't match: { a, b, c } = { "Hello", "World" } # (MatchError) no match of right hand side value: { "Hello",...

When you document your code with @doc, you can supply code examples like so: # myproject/lib/my_module.exs defmodule MyModule do @doc """ Given a number, returns `true` if the number is even, otherwise `false`. ## Example iex> MyModule.even?(2) true ie...

struct FileAttributes { unsigned int ReadOnly: 1; unsigned int Hidden: 1; }; Here, each of these two fields will occupy 1 bit in memory. It is specified by : 1 expression after the variable names. Base type of bit field could be any integral type (8-bit int to 64-bit int). Using u...

C++11 In C++11, compilers are required to implicitly move from a local variable that is being returned. Moreover, most compilers can perform copy elision in many cases and elide the move altogether. As a result of this, returning large objects that can be moved cheaply no longer requires special ha...

Let's have a basic failing program: #include <iostream> void fail() { int *p1; int *p2(NULL); int *p3 = p1; if (p3) { std::cout << *p3 << std::endl; } } int main() { fail(); } Build it (add -g to include debug info): g++ -g -o m...

class API { public: static API& instance(); virtual ~API() {} virtual const char* func1() = 0; virtual void func2() = 0; protected: API() {} API(const API&) = delete; API& operator=(const API&) = delete; }; class WindowsAPI ...

Let's say we need to add a button for each piece of loadedData array (for instance, each button should be a slider showing the data; for the sake of simplicity, we'll just alert a message). One may try something like this: for(var i = 0; i < loadedData.length; i++) jQuery("#container&q...

Bad Example: var location = dbContext.Location .Where(l => l.Location.ID == location_ID) .SingleOrDefault(); return location; Since the above code is simply returning an entity without modifying or adding it, we can avoid tracking cost. Good Ex...

One problem often seen in code is loading all the data. This will greatly increase the load on the server. Let's say I have a model called "location" that has 10 fields in it, but not all the fields are required at the same time. Let's say I only want the 'LocationName' parameter of that...

Let's take an example of a function which receives two arguments and returns a value indicating their sum: def two_sum(a, b): return a + b By looking at this code, one can not safely and without doubt indicate the type of the arguments for function two_sum. It works both when supplied with ...

Django comes with a number of builtin management commands, using python manage.py [command] or, when manage.py has +x (executable) rights simply ./manage.py [command] . The following are some of the most frequently used: Get a list of all available commands ./manage.py help Run your Django ser...