I build my MyObject array with :
MyObject[] myObject = (from MyObject varObj in MyObjects
select varObj).ToArray();
and now, I'd like to extract 3 random MyObject from this array! How can I do it on C#?
Of course, if array lenght is <3 I need to extract all objects!
You can do this via Linq:
Retrieve the items in random order (see Jon Skeet's answer to this SO question)
Select Top(3) of the resulting list using the Take operator
As an example, select 3 processes at random:
var ps = (from p in Process.GetProcesses() orderby Guid.NewGuid() select p).Take(3);
You can also use random.Next() instead of Guids (since strictly speaking, as pointed out by LukeH, Guids are unique, but not random).
MyObject[] myObject = ...;
int upper = 1;
if (myObject.Length > 1)
{
Random r = new Random();
upper = Math.Min(3, myObject.Length);
for (int i = 0; i < upper; i++)
{
int randInd = r.Next(i, myObject.Length);
MyObject temp = myObject[i];
myObject[i] = myObject[randInd];
myObject[randInd] = temp;
}
}
now take elements of the array from 0 to upper.
using Random class of C# you can get random int which are less than a particular number which in your case will be the size of myObject
I am not sure you want unique or they can duplicate.
How about?
Random r = new Random();
int item1 = r.Next(0, myObject.Length);
int item2 = r.Next(0, myObject.Length);
int item3 = r.Next(0, myObject.Length);
var result1 = myObject[item1];
var result2 = myObject[item2];
var result3 = myObject[item3];
No Linq or anything, but it gets the job done.
What about this:
var random = new Random();
var objs = new Object[] { 1, 2, 3, 4, 5, 6, 7, 8 };
var result = objs.OrderBy(o => random.Next(Int32.MaxValue)).Take(3);
A little bit more creative.
var list = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 4, 1, 2, 3, 44, 5, 6 };
Random random = new Random();
var results = list.OrderBy(i => random.Next()).Take(3);
Output:
results: {int[3]}
[0]: 3
[1]: 2
[2]: 5
Related
im trying to multiply each element in three different arrays by 2 with a loop but im having trouble. im really new at this so please excuse any obvious mistakes lol im not even sure ive im using the right kind of loop but heres what i have so far:
int[] firstArray = new int[] { 1, 2, 5, 6, 9 };
int[] secondArray = new int[] { 12, 3, 8, 20, 7 };
int[] thirdArray = new int[] { 2, 4, 6, 8, 10, 12 };
foreach(new int [5] in firstArray)
{
int newArray1= firstArray.Length * 2;
Console.WriteLine(newArray1);
}
i want it to print out the first new array as "2, 4, 10, 12, 18" in the console but when i run it, i get the error type and identifier are both required in a foreach statement.
any help would be greatly appreciated!
Do this with Linq
int[] resultFirstArray = firstArray.Select(r=> r * 2).ToArray();
int[] resultSecondArray = secondArray.Select(r=> r * 2).ToArray();
int[] resultThirdArray = thirdArray.Select(r=> r * 2).ToArray();
Or you can use Array.ConvertAll
Array.ConvertAll converts an entire array. It converts all elements in one array to another type.
var resultFirstArray = Array.ConvertAll(firstArray, x => 2 * x);
var resultSecondArray = Array.ConvertAll(secondArray, x => 2 * x);
var resultThirdArray = Array.ConvertAll(thirdArray, x => 2 * x);
If you just want to show the doubled values:
foreach(int value in firstArray)
{
Console.WriteLine(2 * value);
}
If you want to double the values in the array, then:
for(int i = 0 ; i < firstArray.Length ; i++)
{
firstArray[i] *= 2;
}
Then perhaps to show those values:
foreach(int value in firstArray)
{
Console.WriteLine(value);
}
If you want to create a new array with the values doubled:
var doubledArray = Array.ConvertAll(firstArray, x => 2 * x);
And to output those values:
foreach(int value in doubledArray)
{
Console.WriteLine(value);
}
i want to generate random number from two list. i want to create a function where i pass how much random number from two list.
List<int> integers = new List<int>() { 54, 23, 76, 123, 93, 7, 3489 };
List<int> value2 = new List<int>() { 1, 3, 4, 6, 8, 17, 40 };
i want my result = List<int> result = {54,40,123,17,3,1,3489,76...etc}
When i run again the set of result will be change.
Presently i am using this function that return List
public static List<int> GenerateRandom(int count)
{
// generate count random values.
HashSet<int> candidates = new HashSet<int>();
while (candidates.Count < count)
{
// May strike a duplicate.
candidates.Add(random.Next(1,30));
}
// load them in to a list.
List<int> result = new List<int>();
result.AddRange(candidates);
// shuffle the results:
int i = result.Count;
while (i > 1)
{
i--;
int k = random.Next(i + 1);
int value = result[k];
result[k] = result[i];
result[i] = value;
}
return result;
}
i am calling the function
List<int> vals = GenerateRandom(20);
But i want that the random number from two List<> List<int> integers and List<int> value2 . so how can i do this .
You can do something like this:
var result =
integers.Concat(value2)
.OrderBy(x => random.Next())
.Take(count)
.ToList();
You could write a general-purpose function to give you a random ordering of any number of sequences, like so:
public static IReadOnlyCollection<T> InRandomOrder<T>(Random rng, params IEnumerable<T>[] lists)
{
return lists
.SelectMany(x => x)
.OrderBy(y => rng.Next())
.ToList();
}
You can then pass as many lists as you like and get the contents back in a fully randomised order:
var list1 = new[] {1, 2, 3, 4, 5};
var list2 = new[] {6, 7, 8};
var list3 = new[] {9, 0};
Random rng = new Random();
for (int i = 0; i < 10; ++i)
{
var randomisedFirst5 = InRandomOrder(rng, list1, list2, list3).Take(5);
Console.WriteLine(string.Join(", ", randomisedFirst5));
}
There's a less efficient approach you can use that avoids the need for an instance of Random, but you should only use this for short lists or where you really don't care about performance. It uses Guid.NewGuid() to generate random numbers:
public static IReadOnlyCollection<T> InRandomOrder<T>(params IEnumerable<T>[] lists)
{
return lists
.SelectMany(x => x)
.OrderBy(y => Guid.NewGuid())
.ToList();
}
Even the more efficient approach isn't the fastest. A faster way would be to use reservoir sampling to take the first N items that you want, and put them into an array which you shuffle using Knuth. That would make it a lot faster, at the expense of more complicated code - meaning you should only do it the fast way if it's really needed.
If what you want is to select a number that exists either in list A or B, randomly, you can do:
List<int> integers = new List<int>() { 54, 23, 76, 123, 93, 7, 3489 };
List<int> value2 = new List<int>() { 1, 3, 4, 6, 8, 17, 40 };
List<int> allInOne = new List<int>(integers.Concat(value2));
Random r = new Random(DateTime.Now.Millisecond);
/********************************
For demonstration purposes
********************************/
for(int i = 0; i < 5; i++)
{
var randomListIndex = r.Next(0, allInOne.Count - 1);
Console.WriteLine(allInOne[randomListIndex]);
}
Use KeyValuePair
static void Main(string[] args)
{
List<KeyValuePair<int, int>> results = GenerateRandom(100);
}
static List<int> integers = new List<int>() { 54, 23, 76, 123, 93, 7, 3489 };
static List<int> value2 = new List<int>() { 1, 3, 4, 6, 8, 17, 40 };
static Random random = new Random();
public static List<KeyValuePair<int,int>> GenerateRandom(int count)
{
List<KeyValuePair<int,int>> result = new List<KeyValuePair<int,int>>();
for(int i = 0; i < count; i++)
{
int firstValue = integers[random.Next(0, integers.Count - 1)];
int seconValue = value2[random.Next(0, value2.Count - 1)];
result.Add(new KeyValuePair<int,int>(firstValue,seconValue));
}
return result;
}
I actually made a library a while back that handles some of this stuff : Underscore.cs
It's a nuget package so easy to install, the code to shuffle or take a sample randomly of two lists is :
var ls1 = GenerateRandom(10);
var ls2 = GenerateRandom(20);
var mixer = ls1.Concat(ls2).ToList();
//if you want all of the items shuffled use shuffle
var result = _.List.Shuffle(mixer);
//or if you want a subset randomly sorted use sample
result = _.List.Sample(mixer);
I have two sorted lists as below:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
I want the output to be: {1, 1, 2}
How to do this in C#?
Is there a way using Linq?
Use Intersect:
var commonElements = list1.Intersect(list2).ToList();
The extra 1 means you can't use Intersect because it returns a set.
Here's some code that does what you need:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var grouped1 =
from n in list1
group n by n
into g
select new {g.Key, Count = g.Count()};
var grouped2 =
from n in list2
group n by n
into g
select new {g.Key, Count = g.Count()};
var joined =
from b in grouped2
join a in grouped1 on b.Key equals a.Key
select new {b.Key, Count = Math.Min(b.Count, a.Count)};
var result = joined.SelectMany(a => Enumerable.Repeat(a.Key, a.Count));
CollectionAssert.AreEquivalent(new[] {1, 1, 2}, result);
This works nicely:
var list1 = new List<int>() { 1, 1, 1, 2, 3 };
var list2 = new List<int>() { 1, 1, 2, 2, 4 };
var lookup1 = list1.ToLookup(x => x);
var lookup2 = list2.ToLookup(x => x);
var results = lookup1.SelectMany(l1s => lookup2[l1s.Key].Zip(l1s, (l2, l1) => l1));
While both #Austin Salonen's solution and #Enigmativity's solution work for any given lists, neither take advantage of OP's condition that the lists are sorted.
Given that both lists will be ordered we can do a search in O(n + m) time where n and m are the length of each list. Not entirely sure what the previous solutions big o performance is, but it's definitely slower then O(n + m).
Basically we just walk both lists, moving one or both enumerators based on a comparison check.
var results = new List<int>();
var e1 = list1.GetEnumerator();
var e2 = list2.GetEnumerator();
var hasNext = e1.MoveNext() && e2.MoveNext();
while (hasNext) {
var value1 = e1.Current;
var value2 = e2.Current;
if (value1 == value2) {
results.Add(value1);
hasNext = e1.MoveNext() && e2.MoveNext();
} else if (value1 < value2) {
hasNext = e1.MoveNext();
} else if (value1 > value2) {
hasNext = e2.MoveNext();
}
}
That's it! results will be an empty list if no matches are found.
Note this assumes both lists are in ascending order. If it's descending, just flip the < and > operators.
I am late in answering this question, this might help future visitors.
List<int> p = new List<int> { 1, 1, 1, 2, 3 };
List<int> q = new List<int> { 1, 1, 2, 2, 4 };
List<int> x = new List<int>();
for (int i = 0; i < p.Count; i++ )
{
if (p[i] == q[i])
{
x.Add(p[i]);
}
}
I have an array of five numbers and an array of 2 numbers. How would I find out the largest number among these 7 numbers? Is there a method that can make things easier?
int[] array1 = { 0, 1, 5, 2, 8 };
int[] array2 = { 9, 4 };
int max = array1.Concat(array2).Max();
// max == 9
You can try
decimal max = Math.Max(arr1.Max(), arr2.Max());
Straightforward way:
Math.Max(Math.Max(a,b), c)//on and on for the number of numbers you have
using LINQ:
int[] arr1;
int[] arr2;
int highest = (from number in new List<int>(arr1).AddRange(arr2)
orderby number descending
select number).First();
If you're using 3.5 you could use Linq:
using System.Linq;
var values = new int[] { 1,2,3,4,5 };
var maxValue = values.Max();
Lets say I have this array,
int[] numbers = {1, 3, 4, 9, 2};
How can I delete an element by "name"? , lets say number 4?
Even ArrayList didn't help to delete?
string strNumbers = " 1, 3, 4, 9, 2";
ArrayList numbers = new ArrayList(strNumbers.Split(new char[] { ',' }));
numbers.RemoveAt(numbers.IndexOf(4));
foreach (var n in numbers)
{
Response.Write(n);
}
If you want to remove all instances of 4 without needing to know the index:
LINQ: (.NET Framework 3.5)
int[] numbers = { 1, 3, 4, 9, 2 };
int numToRemove = 4;
numbers = numbers.Where(val => val != numToRemove).ToArray();
Non-LINQ: (.NET Framework 2.0)
static bool isNotFour(int n)
{
return n != 4;
}
int[] numbers = { 1, 3, 4, 9, 2 };
numbers = Array.FindAll(numbers, isNotFour).ToArray();
If you want to remove just the first instance:
LINQ: (.NET Framework 3.5)
int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int numIndex = Array.IndexOf(numbers, numToRemove);
numbers = numbers.Where((val, idx) => idx != numIndex).ToArray();
Non-LINQ: (.NET Framework 2.0)
int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int numIdx = Array.IndexOf(numbers, numToRemove);
List<int> tmp = new List<int>(numbers);
tmp.RemoveAt(numIdx);
numbers = tmp.ToArray();
Edit: Just in case you hadn't already figured it out, as Malfist pointed out, you need to be targetting the .NET Framework 3.5 in order for the LINQ code examples to work. If you're targetting 2.0 you need to reference the Non-LINQ examples.
int[] numbers = { 1, 3, 4, 9, 2 };
numbers = numbers.Except(new int[]{4}).ToArray();
You can also convert your array to a list and call remove on the list. You can then convert back to your array.
int[] numbers = {1, 3, 4, 9, 2};
var numbersList = numbers.ToList();
numbersList.Remove(4);
The code that is written in the question has a bug in it
Your arraylist contains strings of " 1" " 3" " 4" " 9" and " 2" (note the spaces)
So IndexOf(4) will find nothing because 4 is an int, and even "tostring" would convert it to of "4" and not " 4", and nothing will get removed.
An arraylist is the correct way to go to do what you want.
I posted my solution here.
This is a way to delete an array element without copying to another array - just in frame of the same array instance:
public static void RemoveAt<T>(ref T[] arr, int index)
{
for (int a = index; a < arr.Length - 1; a++)
{
// moving elements downwards, to fill the gap at [index]
arr[a] = arr[a + 1];
}
// finally, let's decrement Array's size by one
Array.Resize(ref arr, arr.Length - 1);
}
Removing from an array itself is not simple, as you then have to deal with resizing. This is one of the great advantages of using something like a List<int> instead. It provides Remove/RemoveAt in 2.0, and lots of LINQ extensions for 3.0.
If you can, refactor to use a List<> or similar.
Balabaster's answer is correct if you want to remove all instances of the element. If you want to remove only the first one, you would do something like this:
int[] numbers = { 1, 3, 4, 9, 2, 4 };
int numToRemove = 4;
int firstFoundIndex = Array.IndexOf(numbers, numToRemove);
if (numbers >= 0)
{
numbers = numbers.Take(firstFoundIndex).Concat(numbers.Skip(firstFoundIndex + 1)).ToArray();
}
As a generic extension, 2.0-compatible:
using System.Collections.Generic;
public static class Extensions {
//=========================================================================
// Removes all instances of [itemToRemove] from array [original]
// Returns the new array, without modifying [original] directly
// .Net2.0-compatible
public static T[] RemoveFromArray<T> (this T[] original, T itemToRemove) {
int numIdx = System.Array.IndexOf(original, itemToRemove);
if (numIdx == -1) return original;
List<T> tmp = new List<T>(original);
tmp.RemoveAt(numIdx);
return tmp.ToArray();
}
}
Usage:
int[] numbers = {1, 3, 4, 9, 2};
numbers = numbers.RemoveFromArray(4);
You can do in this way:
int[] numbers= {1,3,4,9,2};
List<int> lst_numbers = new List<int>(numbers);
int required_number = 4;
int i = 0;
foreach (int number in lst_numbers)
{
if(number == required_number)
{
break;
}
i++;
}
lst_numbers.RemoveAt(i);
numbers = lst_numbers.ToArray();
' To remove items from string based on Dictionary key values.
' VB.net code
Dim stringArr As String() = "file1,file2,file3,file4,file5,file6".Split(","c)
Dim test As Dictionary(Of String, String) = New Dictionary(Of String, String)
test.Add("file3", "description")
test.Add("file5", "description")
stringArr = stringArr.Except(test.Keys).ToArray()
public int[] DeletePart(int position, params int[] numbers)
{
int[] result = new int[numbers.Length - 1];
int z=0;
for (int i = 0; i < numbers.Length; i++)
{
if (position - 1 != i)
{
result[z] = numbers[i];
z++;
}
}
return result;
}
We can delete array elements by using for loops and continue statements:
string[] cars = {"volvo", "benz", "ford", "bmw"};
for (int i = 0; i < cars.Length; i++)
{
if (cars[i] == "benz")
{
continue;
}
Console.WriteLine(cars[i]);
}