Tutorial by Examples: r

You can create a DataFrame from a list of simple tuples, and can even choose the specific elements of the tuples you want to use. Here we will create a DataFrame using all of the data in each tuple except for the last element. import pandas as pd data = [ ('p1', 't1', 1, 2), ('p1', 't2', 3, 4)...

By default, all types in TypeScript allow null: function getId(x: Element) { return x.id; } getId(null); // TypeScript does not complain, but this is a runtime error. TypeScript 2.0 adds support for strict null checks. If you set --strictNullChecks when running tsc (or set this flag in you...

val num = 42d Print two decimal places for num using f println(f"$num%2.2f") 42.00 Print num using scientific notation using e println(f"$num%e") 4.200000e+01 Print num in hexadecimal with a println(f"$num%a") 0x1.5p5 Other format strings can be found ...

Move Blue to the beginning of the array: NSMutableArray *myColors = [NSMutableArray arrayWithObjects: @"Red", @"Green", @"Blue", @"Yellow", nil]; NSUInteger fromIndex = 2; NSUInteger toIndex = 0; id blue = [[[self.array objectAtIndex:fromIndex] retain]...

Every authenticated user has a Firebase uid that's unique across all providers and is returned in the result of every authentication method. A good way to store your user's data is to create a node to keep all the users's data and to protect it using your security rules - Database { "use...

You can define scripts that can be executed or are triggered before or after another script. { "scripts": { "pretest": "scripts/pretest.js", "test": "scripts/test.js", "posttest": "scripts/posttest.js" } } ...

Evaluates to the first truthy argument if either one of the arguments is truthy. If both arguments are falsey, evaluates to the second argument. x = True y = True z = x or y # z = True x = True y = False z = x or y # z = True x = False y = True z = x or y # z = True x = False y = Fa...

Oracle's CONNECT BY functionality provides many useful and nontrivial features that are not built-in when using SQL standard recursive CTEs. This example replicates these features (with a few additions for sake of completeness), using SQL Server syntax. It is most useful for Oracle developers findin...

Deleting files The unlink function deletes a single file and returns whether the operation was successful. $filename = '/path/to/file.txt'; if (file_exists($filename)) { $success = unlink($filename); if (!$success) { throw new Exception("Cannot delete $filename&qu...

An implicit conversion allows the compiler to automatically convert an object of one type to another type. This allows the code to treat an object as an object of another type. case class Foo(i: Int) // without the implicit Foo(40) + 2 // compilation-error (type mismatch) // defines how t...

This example will guide you through setting up a back end serving an a Hello World HTML page. Installing Requirements Order matters for this step! sudo apt-get install apache2 Setting up the HTML Apache files live in /var/www/html/. Lets quickly get there. Make sure you're in your root ...

You can use the filter(_:) method on SequenceType in order to create a new array containing the elements of the sequence that satisfy a given predicate, which can be provided as a closure. For example, filtering even numbers from an [Int]: let numbers = [22, 41, 23, 30] let evenNumbers = number...

This function lets you iterate over the Cartesian product of a list of iterables. For example, for x, y in itertools.product(xrange(10), xrange(10)): print x, y is equivalent to for x in xrange(10): for y in xrange(10): print x, y Like all python functions that accept a v...

Any data structure that supports __getitem__ can have their nested structure formatted: person = {'first': 'Arthur', 'last': 'Dent'} '{p[first]} {p[last]}'.format(p=person) # 'Arthur Dent' Object attributes can be accessed using getattr(): class Person(object): first = 'Zaphod' la...

Lambda functions in C++ are syntactic sugar that provide a very concise syntax for writing functors. As such, equivalent functionality can be obtained in C++03 (albeit much more verbose) by converting the lambda function into a functor: // Some dummy types: struct T1 {int dummy;}; struct T2 {int ...

There are two main versions of IntelliJ IDEA: the Community edition and the Ultimate edition. The Community edition is free and is not lacking for features in terms of Java SE development. Windows & Linux Download IntelliJ IDEA from the JetBrains website, and follow installation procedures. If...

Introduction: This simple function generates infinite series of numbers. For example... for number in itertools.count(): if number > 20: break print(number) Note that we must break or it prints forever! Output: 0 1 2 3 4 5 6 7 8 9 10 Arguments: count() ta...

There are a couple of ways to delete a column in a DataFrame. import numpy as np import pandas as pd np.random.seed(0) pd.DataFrame(np.random.randn(5, 6), columns=list('ABCDEF')) print(df) # Output: # A B C D E F # 0 -0.895467 0.386902...

Generics are placeholders for types, allowing you to write flexible code that can be applied across multiple types. The advantage of using generics over Any is that they still allow the compiler to enforce strong type-safety. A generic placeholder is defined within angle brackets <>. Generic...

Returns a Boolean indicating if the class conform the protocol: [MyClass conformsToProtocol:@protocol(MyProtocol)];