Tutorial by Examples: u

A Bag/ultiset stores each object in the collection together with a count of occurrences. Extra methods on the interface allow multiple copies of an object to be added or removed at once. JDK analog is HashMap<T, Integer>, when values is count of copies this key. TypeGuavaApache Commons Collec...

This multimap allows duplicate key-value pairs. JDK analogs are HashMap<K, List>, HashMap<K, Set> and so on. Key's orderValue's orderDuplicateAnalog keyAnalog valueGuavaApacheEclipse (GS) CollectionsJDKnot definedInsertion-orderyesHashMapArrayListArrayListMultimapMultiValueMapFastListMu...

Suppose we want to count how many counties are there in Texas: var counties = dbContext.States.Single(s => s.Code == "tx").Counties.Count(); The query is correct, but inefficient. States.Single(…) loads a state from the database. Next, Counties loads all 254 counties with all of the...

Types of columns can be checked by .dtypes atrribute of DataFrames. In [1]: df = pd.DataFrame({'A': [1, 2, 3], 'B': [1.0, 2.0, 3.0], 'C': [True, False, True]}) In [2]: df Out[2]: A B C 0 1 1.0 True 1 2 2.0 False 2 3 3.0 True In [3]: df.dtypes Out[3]: A int64 ...

select_dtypes method can be used to select columns based on dtype. In [1]: df = pd.DataFrame({'A': [1, 2, 3], 'B': [1.0, 2.0, 3.0], 'C': ['a', 'b', 'c'], 'D': [True, False, True]}) In [2]: df Out[2]: A B C D 0 1 1.0 a True 1 2 2.0 b False 2...

get_dtype_counts method can be used to see a breakdown of dtypes. In [1]: df = pd.DataFrame({'A': [1, 2, 3], 'B': [1.0, 2.0, 3.0], 'C': ['a', 'b', 'c'], 'D': [True, False, True]}) In [2]: df.get_dtype_counts() Out[2]: bool 1 float64 1 int64 1 obje...

This example shows how to create a prepared statement with an insert statement with parameters, set values to those parameters and then executing the statement. Connection connection = ... // connection created earlier try (PreparedStatement insert = connection.prepareStatement( "i...

In PaaS sites such as Heroku, it is usual to receive the database information as a single URL environment variable, instead of several parameters (host, port, user, password...). There is a module, dj_database_url which automatically extracts the DATABASE_URL environment variable to a Python dictio...

When you create a function in TypeScript you can specify the data type of the function's arguments and the data type for the return value Example: function sum(x: number, y: number): number { return x + y; } Here the syntax x: number, y: number means that the function can accept two argum...

Example: function hello(name: string): string { return `Hello ${name}!`; } Here the syntax name: string means that the function can accept one name argument and this argument can only be string and (...): string { means that the return value can only be a string Usage: hello('StackOverfl...

Android Studio can configure Kotlin automatically in an Android project. Install the plugin To install the Kotlin plugin, go to File > Settings > Editor > Plugins > Install JetBrains Plugin... > Kotlin > Install, then restart Android Studio when prompted. Configure a project Cr...

TeX formulae can be inserted in the plot using the rc function import matplotlib.pyplot as plt plt.rc(usetex = True) or accessing the rcParams: import matplotlib.pyplot as plt params = {'tex.usetex': True} plt.rcParams.update(params) TeX uses the backslash \ for commands and symbols, whic...

In order to include plots created with matplotlib in TeX documents, they should be saved as pdf or eps files. In this way, any text in the plot (including TeX formulae) is rendered as text in the final document. import matplotlib.pyplot as plt plt.rc(usetex=True) x = range(0, 10) y = [t**2 for t...

You can search Docker Hub for images by using the search command: docker search <term> For example: $ docker search nginx NAME DESCRIPTION STARS OFFICIAL AUTOMATED nginx Official build of Nginx. ...

public class MyObject{ public DateTime? TestDate { get; set; } public Func<MyObject, bool> DateIsValid = myObject => myObject.TestDate.HasValue && myObject.TestDate > DateTime.Now; public void DoSomething(){ //We can do this: if(this.TestDate....

Dart has a robust async library, with Future, Stream, and more. However, sometimes you might run into an asynchronous API that uses callbacks instead of Futures. To bridge the gap between callbacks and Futures, Dart offers the Completer class. You can use a Completer to convert a callback into a Fut...

The following example creates a canvas with 2 points and 1 line in between. You will be able to move the point and the line around. from kivy.app import App from kivy.graphics import Ellipse, Line from kivy.uix.boxlayout import BoxLayout class CustomLayout(BoxLayout): def __init__(se...

When defining a function, use {param1, param2, …} to specify named parameters: void enableFlags({bool bold, bool hidden}) { // ... } When calling a function, you can specify named parameters using paramName: value enableFlags(bold: true, hidden: false);

A linked list is a linear collection of data elements, called nodes, which are linked to other node(s) by means of a "pointer." Below is a singly linked list with a head reference. ┌─────────┬─────────┐ ┌─────────┬─────────┐ HEAD ──▶│ data │"pointer"│──▶...

It's a VBA Best Practice to always specify which workbook your VBA code refers. If this specification is omitted, then VBA assumes the code is directed at the currently active workbook (ActiveWorkbook). '--- the currently active workbook (and worksheet) is implied Range("A1").value = 3.1...