Tutorial by Examples: ti

Configuring and switching Java versions on Linux using alternatives

Using Alternatives Many Linux distributions use the alternatives command for switching between different versions of a command. You can use this for switching between different versions of Java installed on a machine. In a command shell, set $JDK to the pathname of a newly installed JDK; e.g....

Java Language • Installing Java (Standard Edition)

How to change MultiIndex columns to standard columns

Given a DataFrame with MultiIndex columns # build an example DataFrame midx = pd.MultiIndex(levels=[['zero', 'one'], ['x','y']], labels=[[1,1,0,],[1,0,1,]]) df = pd.DataFrame(np.random.randn(2,3), columns=midx) In [2]: df Out[2]: one zero y x ...

pandas • MultiIndex

How to change standard columns to MultiIndex

Start with a standard DataFrame df = pd.DataFrame(np.random.randn(2,3), columns=['a','b','c']) In [91]: df Out[91]: a b c 0 -0.911752 -1.405419 -0.978419 1 0.603888 -1.187064 -0.035883 Now to change to MultiIndex, create a MultiIndex object and assign it to df....

pandas • MultiIndex

MultiIndex Columns

MultiIndex can also be used to create DataFrames with multilevel columns. Just use the columns keyword in the DataFrame command. midx = pd.MultiIndex(levels=[['zero', 'one'], ['x','y']], labels=[[1,1,0,],[1,0,1,]]) df = pd.DataFrame(np.random.randn(6,4), columns=midx) In [86]: df Out[86]: ...

pandas • MultiIndex

Connection to a cluster

es = Elasticsearch(hosts=hosts, sniff_on_start=True, sniff_on_connection_fail=True, sniffer_timeout=60, sniff_timeout=10, retry_on_timeout=True)

Elasticsearch • Python Interface

Iterating Maps

Map has three methods which returns iterators: .keys(), .values() and .entries(). .entries() is the default Map iterator, and contains [key, value] pairs. const map = new Map([[1, 2], [3, 4]]); for (const [key, value] of map) { console.log(`key: ${key}, value: ${value}`); // logs: // ke...

JavaScript • Map

Getting and setting elements

Use .get(key) to get value by key and .set(key, value) to assign a value to a key. If the element with the specified key doesn't exist in the map, .get() returns undefined. .set() method returns the map object, so you can chain .set() calls. const map = new Map(); console.log(map.get(1)); // und...

JavaScript • Map

Getting the number of elements of a Map

To get the numbers of elements of a Map, use the .size property: const map = new Map([[1, 2], [3, 4]]); console.log(map.size); // 2

JavaScript • Map

Setting state Added of a single entity

EntityState.Added can be set in two fully equivalent ways: By setting the state of its entry in the context: context.Entry(entity).State = EntityState.Added; By adding it to a DbSet of the context: context.Entities.Add(entity); When calling SaveChanges, the entity will be inse...

Entity Framework • Managing entity state

Remove unused alternative resources

All libraries come with resources that are not necessary useful to your application. For example Google Play Services comes with translations for languages your own application don’t even support. You can configure the build.gradle file to specify which resource you want to keep. For example: de...

android-gradle • Shrink Code and Resources

Setting state Added of an object graph

Setting the state of an object graph (a collection of related entities) to Added is different than setting a single entity as Added (see this example). In the example, we store planets and their moons: Class model public class Planet { public Planet() { Moons = new HashSet<...

Entity Framework • Managing entity state

Set frame rate using requestAnimationFrame

Using requestAnimationFrame may on some systems update at more frames per second than the 60fps. 60fps is the default rate if the rendering can keep up. Some systems will run at 120fps maybe more. If you use the following method you should only use frame rates that are integer divisions of 60 so th...

html5-canvas • Animation

Locating comments

To locate comments in BeautifulSoup, use the text (or string in the recent versions) argument checking the type to be Comment: from bs4 import BeautifulSoup from bs4 import Comment data = """ <html> <body> <div> <!-- desired text --&gt...

beautifulsoup • Locating elements

The %timeit and `%time` magics

The %timeit magic runs the given code many times, then returns the speed of the fastest result. In [1]: %timeit sum(range(100000)) 100 loops, best of 3: 2.91 ms per loop The %%timeit cell magic can be used to time blocks of code. In [2]: %%timeit ...: a = 0 ...: for i in range(100000):...

ipython • Magics

Reading/Writing Data Using System.IO.File

First, let's see three different ways of extracting data from a file. string fileText = File.ReadAllText(file); string[] fileLines = File.ReadAllLines(file); byte[] fileBytes = File.ReadAllBytes(file); On the first line, we read all the data in the file as a string. On the second line, we r...

.NET Framework • System.IO

Conversion by explicit constructor or explicit conversion function

A conversion that involves calling an explicit constructor or conversion function can't be done implicitly. We can request that the conversion be done explicitly using static_cast. The meaning is the same as that of a direct initialization, except that the result is a temporary. class C { std:...

C++ • Explicit type conversions

Date and Time

These types are in all versions of SQL Server datetime smalldatetime These types are in all versions of SQL Server after SQL Server 2012 date datetimeoffset datetime2 time

Microsoft SQL Server • Data Types

Initializing object properties with null

All modern JavaScript JIT compilers trying to optimize code based on expected object structures. Some tip from mdn. Fortunately, the objects and properties are often "predictable", and in such cases their underlying structure can also be predictable. JITs can rely on this to make pred...

JavaScript • Performance Tips

Multiprocessing using built-in fork functions

You can use built-in functions to run PHP processes as forks. This is the most simple way to achieve parallel work if you don't need your threads to talk to each other. This allows you to put time intensive tasks (like uploading a file to another server or sending an email) to another thread so you...

PHP • Multiprocessing

Installation or Setup

1 Tag Name Represents a tag name available in the DOM. For example $('p') selects all paragraphs <p> in the document. 2 Tag ID Represents a tag available with the given ID in the DOM. For example $('#some-id') selects the single element in the document that has an ID of some-id. 3 ...

jquery-selectors • Getting started with jquery-selectors