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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....

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]: ...

If you need to copy a database from one server to another, you have two options: Option 1: Store the dump file in the source server Copy the dump file to your destination server Load the dump file into your destination server On the source server: mysqldump [options] > dump.sql On th...

To remove all elements from a Map, use the .clear() method: map.clear(); Example: const map = new Map([[1, 2], [3, 4]]); console.log(map.size); // 2 map.clear(); console.log(map.size); // 0 console.log(map.get(1)); // undefined

To remove an element from a map use the .delete() method. map.delete(key); Example: const map = new Map([[1, 2], [3, 4]]); console.log(map.get(3)); // 4 map.delete(3); console.log(map.get(3)); // undefined This method returns true if the element existed and has been removed, otherwise fal...

To check if a key exists in a Map, use the .has() method: map.has(key); Example: const map = new Map([[1, 2], [3, 4]]); console.log(map.has(1)); // true console.log(map.has(2)); // false

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...

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...

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

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...

To enable code shrinking with ProGuard, add minifyEnabled true to the appropriate build type in your build.gradle file. android { buildTypes { release { minifyEnabled true proguardFiles getDefaultProguardFile(‘proguard-android.txt'), 'pro...

To enable resource shrinking, set the shrinkResources property to true in your build.gradle file. android { ... buildTypes { release { minifyEnabled true shrinkResources true proguardFiles getDefaultProguardFile('proguard-android.txt'), 'p...

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<...

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...

Building project dependencies can sometimes be a tedious task. Instead of publishing a package version to NPM and installing the dependency to test the changes, use npm link. npm link creates a symlink so the latest code can be tested in a local environment. This makes testing global tools and proje...

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...

R provides two additional looping constructs, while and repeat, which are typically used in situations where the number of iterations required is indeterminate. The while loop The general form of a while loop is as follows, while (condition) { ## do something ## in loop body } whe...

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...

Iterating over connected serial ports using System.IO.Ports; string[] ports = SerialPort.GetPortNames(); for (int i = 0; i < ports.Length; i++) { Console.WriteLine(ports[i]); } Instantiating a System.IO.SerialPort object using System.IO.Ports; SerialPort port = new SerialPort(); ...

This example is about replacing a List element while ensuring that the replacement element is at the same position as the element that is replaced. This can be done using these methods: set(int index, T type) int indexOf(T type) Consider an ArrayList containing the elements "Program sta...