Javascript Hash

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There are several types of Java data that are used to store values. Each stores data type values ‚Äã‚Äãdifferently and offers a range of methods that can be used to manipulate the stored values. For example, numbers can be manipulated using math functions in Java.

HashSet is a data type in Java used to create a mathematical set. HashSet is part of the Java collections framework and allows you to store data using the hash table data type.

This tutorial will discuss the basics of the Java HashSet class and how it can be used. We will also discuss the main methods offered by HashSet to retrieve and manipulate data stored in a set.

Java Defines and HashSet

Sets are Java collections that they cannot contain double elements. While a list can contain the same value times of several, sets cannot contain a specific value once.

Sets can be useful in a wide variety of situations. For example, if you create a program for a local cafe that stores the phone numbers of their loyal customers, you want the same phone number to appear only once in the list.

Java, the set type is an interface, in order to use it we need to use one of the classes associated with the data type. The HashSet class implements the data type set and is used to create a set that uses the hash table data structure.

Before we can start working with HashSet, we need to import the HashSet package into our code. Here is the code we can use to import HashSet into our code:

import java.util.HashSet;

Now we have imported the HashSet, we can start working with the data type

Java Create a HashSet

Here is the syntax you can use to create a Java HashSet:.

HashSet variable_name = new HashSet <> (capacity, loadfactor);

The main components of a HashSet are as follows:

  • HashSet indicates our program that we want to declare HashSet.
  • DataType is the type of data that is occupied by the values ‚Äã‚Äãstored in the hash set.
  • variable_name is the name of our hash set.
  • new HashSet <> Initializes a HashSet and assigns it to variable_name.
  • capacity indicates how many values ‚Äã‚Äãthe hash set can store. By default it is set to 8. (optional)
  • loadfactor specifies that when a hash set is filled with a certain amount, the items in the table are moved in a new table twice the size of the original table . By default, it is set to 0.75 (or 75% of capacity). ( optional)

Suppose we want to create a HashSet that’s me morizzi the list of fruits sold on our fruit stand, we could do it using the following code:

In our code, we’ve created a HashSet called fruits which allows you to store string values. Now we have a HashSet ready, we can start working on using HashSet methods.

Add Element

The add () method adds a specified element to a HashSet in Java. Suppose we want to add the Pear, Grapefruit and Mango values ‚Äã‚Äãto our fruit list. We could do this using this code:

When we run our code, the following response is returned:

["pear", "Gra pefruit", "Mango "]

Break from Descended our code. First, we import the HashSet class from java.util, then we initialize a class called AddFruits, which stores our program code. On the next line, we declare a HashSet called fruits which stores the string values.

Next, we use the add () method to add three values ‚Äã‚Äãto our fruit hash set: pear, grapefruit, and mango. Finally, we print the contents of the fruit hash set method to the console.

Deleting an Element

The deletion () can be used to delete an item from a HashSet.

Suppose our fruit stand decided to sell off due to lack of mango trees in demand. Therefore, we want to remove the Mango entry from the HashSet that we created earlier. We could do it using this code:

Our code returns:

["pear", "grapefruit"]

our code removed Mango from our original HashSet and returns the modified HashSet method with the other two values.

Additionally, the removeAll () is used to remove all items from a collection. So if we decided to start from scratch and create a new fruit list, we could use removeAll () to remove all of the items from our set. Here is the code we could use to remove all the elements in our HashSet "fruits":

Our code returns an empty hash set. []

Accessing elements

Unlike Java arrays, games are not indexed. So if we want to access the values ‚Äã‚Äãin our set, we have to use the iterator () method and iterate through each value. iterator () is part of the "java.util.Iterator" package, so we’ll need to import the Iterator package before we can use the iterator () method

Here is a program we could use to iterate through each fruit in our fruit array from earlier and print it to the console:

Our code returns:

Pear

Grapefruit

Mango

In our code, first we import the HashSet and Iterator libraries from java.util, we declare a class called RetrieveFruits where our program code is located. Next, we have a HashSet called initialize fruit and assign it three values: Pear, Grapefruit, Mango and

on the next line. , we initialize an iterator, which lets us iterate through each element in our HashSet. Next, we create a while loop that examines each fruit HashSet element and prints to the console.

Set operations

The class HashSet. Is a set, then the class can access the different tuning operations offered by the data type set There are four main tuning operations that can be used with the HashSet class: union, intersection, subset, and difference. Let’s see how each of these methods works individually.

HashSet fusion method

The addAll () can be used to perform a merge between two sets. In other words, addAll () allows you to merge the contents of two sets together.

Suppose we kept our fruits in two hash sets. The first set of hashes, fruits, stores a list of generic fruits that we sell at our booth. The second set of hashes, berries, stores the berries that we sell. We have decided to merge these two sets.

We can join our two sets using the following code:

The return of the addAll () method:

[pear, grapefruit, mango, strawberry, raspberry, blueberry]

As you can see, our code merged our fruit and berry hash sets into the fruit hash> set. Then our code prints the modified hash set to the console

HashSet Intersection

Intersection is used to find common values ‚Äã‚Äãin two datasets. We can use retentionAll () to intersect on two datasets.

Suppose you have our berry and fruit lists and want to make sure there are no common values. We could use the code from our Merge example with a modification to do this:

Our code returns:. []

Instead of using addAll (), we use retentionAll () to perform an intersection. As you can see, because there are no common values ‚Äã‚Äãbetween our fruit and berry lists, an empty hash set is returned. This tells us that there are no duplicate values in our lists, which is exactly what we wanted.

HashSet method subset

The containAll () is used to check if a set is a subset of another set. In other words, containsAll () checks if a set contains only values ‚Äã‚Äãfrom another set.

Suppose we want to check if our arrays list was a sub - together ours. fruit list. We could do it using this code:

Our code returns: false. The berry values ‚Äã‚Äãwe defined in our Union example are not the same as in fruits. Thus, our code returns false.

HashSet Difference

The removeAll () method is used to calculate the difference between two sets. Suppose you have a list of fruits and a list of summer fruits and winter berries, and you want to know the difference between the two. We could use this code to calculate the difference:

Our code returns:

[pear]

We ran a search any differences in the summer_fruits list and checked which values ‚Äã‚Äãonly existed in the summer_fruits list. In this case, Pear is the only fruit that only exists in the summer_fruits list, our list returned a value. Pear

conclusion

HashSet class tools and Set interface with Java hash tables. HashSet is commonly used if you want to access elements at random or store a list of items that can not contain values doubled.

This tutorial discussed the basics of Java HashSet and, referring to examples, explored how to declare and manipulate Java HashSet.You are now ready to start using the Java HashSet class like a pro!

👻 Read also: what is the best laptop for engineering students?

Javascript Hash __del__: Questions

__del__

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

Javascript Hash __del__: Questions

__del__

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #2


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #3

Python syntax to delete a file

import os
os.remove("/tmp/<file_name>.txt")

Or

import os
os.unlink("/tmp/<file_name>.txt")

Or

pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()

Path.unlink(missing_ok=False)

Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

#!/usr/bin/python
import os
myfile="/tmp/foo.txt"

## If file exists, delete it ##
if os.path.isfile(myfile):
    os.remove(myfile)
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

#!/usr/bin/python
import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
try:
    os.remove(myfile)
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))

RESPECTIVE OUTPUT

Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder

shutil.rmtree()

Example for shutil.rmtree()

#!/usr/bin/python
import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
try:
    shutil.rmtree(mydir)
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

__delete__

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "D:zjm_codea.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

But is there not a simpler way to do this?

1055

Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]

We hope this article has helped you to resolve the problem. Apart from Javascript Hash, check other __del__-related topics.

Want to excel in Python? See our review of the best Python online courses 2022. If you are interested in Data Science, check also how to learn programming in R.

By the way, this material is also available in other languages:



Ken Chamberlet

Texas | 2022-11-30

Thanks for explaining! I was stuck with Javascript Hash for some hours, finally got it done 🤗. I just hope that will not emerge anymore

Angelo Gonzalez

Paris | 2022-11-30

find is always a bit confusing 😭 Javascript Hash is not the only problem I encountered. Checked yesterday, it works!

Walter Chamberlet

Shanghai | 2022-11-30

Thanks for explaining! I was stuck with Javascript Hash for some hours, finally got it done 🤗. I am just not quite sure it is the best method

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