Tutorial by Examples: pre

Common table expressions support extracting portions of larger queries. For example: WITH sales AS ( SELECT orders.ordered_at, orders.user_id, SUM(orders.amount) AS total FROM orders GROUP BY orders.ordered_at, orders.user_id ) SELECT sales.ordered_at, sales.total,...

Occasionally you'd want to catch an exception and throw it from a different thread or method while preserving the original exception stack. This can be done with ExceptionDispatchInfo: using System.Runtime.ExceptionServices; void Main() { ExceptionDispatchInfo capturedException = null; ...

prepend() - Insert content, specified by the parameter, to the beginning of each element in the set of matched elements. 1. prepend( content [, content ] ) // with html string jQuery('#parent').prepend('<span>child</span>'); // or you can use jQuery object jQuery('#parent').prepend(...

Defining a method in Ruby 2.x returns a symbol representing the name: class Example puts def hello end end #=> :hello This allows for interesting metaprogramming techniques. For instance, methods can be wrapped by other methods: class Class def logged(name) original_method...

$parameters = @{ From = 'from@bar.com' To = 'to@bar.com' Subject = 'Email Subject' Attachments = @('C:\files\samplefile1.txt','C:\files\samplefile2.txt') BCC = 'bcc@bar.com' Body = 'Email body' BodyAsHTML = $False CC = 'cc@bar.com' Credential = Get-Crede...

Elm has a special syntax for lambda expressions or anonymous functions: \arguments -> returnedValue For example, as seen in List.filter: > List.filter (\num -> num > 1) [1,2,3] [2,3] : List number More to the depth, a backward slash, \, is used to mark the beginning of lambda ex...

All files are in folder files. First create list of DataFrames and then concat them: import pandas as pd import glob #a.csv #a,b #1,2 #5,8 #b.csv #a,b #9,6 #6,4 #c.csv #a,b #4,3 #7,0 files = glob.glob('files/*.csv') dfs = [pd.read_csv(fp) for fp in files] #duplicated ind...

Responses can be written to a http.ResponseWriter using templates in Go. This proves as a handy tool if you wish to create dynamic pages. (To learn how Templates work in Go, please visit the Go Templates Documentation page.) Continuing with a simple example to utilise the html/template to respond ...

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...

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...

Boolean logic expressions, in addition to evaluating to True or False, return the value that was interpreted as True or False. It is Pythonic way to represent logic that might otherwise require an if-else test. And operator The and operator evaluates all expressions and returns the last expressi...

The search pattern can also be a regular expression. Running: grep '^[A-Z]' someFile.txt When someFile.txt contains: fred 14 m foo sam 68 m bar christina 83 f baz bob 22 m qux Sam 41 m quux Will produce the output: Sam 41 m quux since this is the only line in someFile.txt starting wi...

Using filterUsingPredicate: This Evaluates a given predicate against the arrays content and return objects that match. Example: NSMutableArray *array = [NSMutableArray array]; [array setArray:@[@"iOS",@"macOS",@"tvOS"]]; NSPredicate *predicate = [N...

A distinctive syntactic peculiarity of C is that declarations mirror the use of the declared object as it would be in a normal expression. The following set of operators with identical precedence and associativity are reused in declarators, namely: the unary * "dereference" operator wh...

SharedPreferences allows you to store primitive data types only (boolean, float, long, int, String, and string set). You cannot store more complex objects in SharedPreferences, and as such is really meant to be a place to store user settings or similar, it's not meant to be a database to keep user d...

>>> expression = '5 + 3 * a' >>> a = 5 >>> result = eval(expression) >>> result 20

compile built-in function can be used to precompile an expression to a code object; this code object can then be passed to eval. This will speed up the repeated executions of the evaluated code. The 3rd parameter to compile needs to be the string 'eval'. >>> code = compile('a * b + c', '&l...

>>> variables = {'a': 6, 'b': 7} >>> eval('a * b', globals=variables) 42 As a plus, with this the code cannot accidentally refer to the names defined outside: >>> eval('variables') {'a': 6, 'b': 7} >>> eval('variables', globals=variables) Traceback (most ...

You can also use regular expressions to split a string. For example, import re data = re.split(r'\s+', 'James 94 Samantha 417 Scarlett 74') print( data ) # Output: ['James', '94', 'Samantha', '417', 'Scarlett', '74']

Predicates that produce side effects leave the realm of pure logic. These are for example: writeq/1 read/1 format/2 Side effects are phenomena that cannot be reasoned about within the program. For example, deletion of a file or output on the system terminal.