Tutorial by Examples: ti

When it comes to geographic data, R shows to be a powerful tool for data handling, analysis and visualisation. Often, spatial data is avaliable as an XY coordinate data set in tabular form. This example will show how to create a spatial data set from an XY data set. The packages rgdal and sp provi...

rgdal ESRI shape files can easily be imported into R by using the function readOGR() from the rgdal package. library(rgdal) shp <- readORG(dsn = "/path/to/your/file", layer = "filename") It is important to know, that the dsn must not end with / and the layer does not all...

Concurrent collections are a generalization of thread-safe collections, that allow for a broader usage in a concurrent environment. While thread-safe collections have safe element addition or removal from multiple threads, they do not necessarily have safe iteration in the same context (one may not...

'Prefer composition over inheritance' is an important and popular programming principle, used to assign behaviors to objects, as opposed to inheriting many often unneeded behaviors. Behaviour factories var speaker = function (state) { var noise = state.noise || 'grunt'; return { ...

The difference between size and count is: size counts NaN values, count does not. df = pd.DataFrame( {"Name":["Alice", "Bob", "Mallory", "Mallory", "Bob" , "Mallory"], "City":["Seattle", &q...

A method defined in an interface is by default public abstract. When an abstract class implements an interface, any methods which are defined in the interface do not have to be implemented by the abstract class. This is because a class that is declared abstract can contain abstract method declaratio...

var a:Object; trace(a); // null trace(a.b); // Error 1009 Here, an object reference is declared, but is never assigned a value, be it with new or assignment of a non-null value. Requesting its properties or method results in a 1009 error.

x=anObject.aProperty.anotherProperty.getSomething().data; Here, any object before the dot can end up being null, and using methods that return complex objects only increases the complication to debug the null error. Worst case if the method is prone to extraneous failures, say retrieving data ove...

s=this.getChildByName("garbage"); if (s.parent==this) {...} getChildByName() is one of the many functions that can return null if an error occurred when processing its input. Therefore, if you are receiving an object from any function that can possibly return null, check for null first...

prerequisite of scrapy installation: Python 2.7 or above 3.3 pip and setuptools Python packages. lxml OpenSSL. You can install Scrapy using pip. To install using pip run: pip install Scrapy Platform specific installation Anaconda This is the recommended way to install Scrapy. ...

4.0 Declare an associative array declare -A aa Declaring an associative array before initialization or use is mandatory. Initialize elements You can initialize elements one at a time as follows: aa[hello]=world aa[ab]=cd aa["key with space"]="hello world" You can al...

Get the list of inialized indexes in an array $ arr[2]='second' $ arr[10]='tenth' $ arr[25]='twenty five' $ echo ${!arr[@]} 2 10 25

Windows There are two options how to install Kivy: First ensure python tools are up-to-date. python -m pip install --upgrade pip wheel setuptools Then install the basic dependencies. python -m pip install docutils pygments pypiwin32 kivy.deps.sdl2 kivy.deps.glew Although Kivy already has p...

You can install three.js via npm: npm install three You can add it from a CDN to your HTML: <script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r83/three.js"></script> You can use the three.js editor to give it a try and download the project as an ex...

Arithmetic if statement allows one to use three branches depending on the result of an arithmetic expression if (arith_expr) label1, label2, label3 This if statement transfers control flow to one of the labels in a code. If the result of arith_expr is negative label1 is involved, if the result i...

Detailed instructions on getting tfs set up or installed.

This validation restricts the insertion of only numeric values. class Player < ApplicationRecord validates :points, numericality: true validates :games_played, numericality: { only_integer: true } end Besides :only_integer, this helper also accepts the following options to add constrai...

This helper validates that the specified attributes are not empty. class Person < ApplicationRecord validates :name, presence: true end Person.create(name: "John").valid? # => true Person.create(name: nil).valid? # => false You can use the absence helper to validate th...

Use following methods if you want to skip the validations. These methods will save the object to the database even if it is invalid. decrement! decrement_counter increment! increment_counter toggle! touch update_all update_attribute update_column update_columns update_counters You ca...

class Person < ApplicationRecord validates :name, length: { minimum: 2 } validates :bio, length: { maximum: 500 } validates :password, length: { in: 6..20 } validates :registration_number, length: { is: 6 } end The possible length constraint options are: :minimum - The attribut...