C# List Remove ExamplesUse Remove, RemoveRange and RemoveAt on Lists. Delete elements by value and index.
Remove, List. For a C# List, the Remove[] method eliminates elements. We remove by index, value, or by condition [a lambda]. Each approach has its proper use.
List
Method notes. The Remove method is effective for removing by value. But we may also use RemoveAt to remove an element at an index.
Remove example. We can remove based on the element value [with Remove], or based on the index [with RemoveAt]. This is not equivalent to assigning an element to null.
Step 1 We create a List and add several strings to it. This List is used to demonstrate how Remove methods work.
Step 2 We call Remove to remove an element by its value. So the element with the value "BB" is removed.
Step 3 The example shows RemoveAt. It removes the element at index 1, which is the second element, "BB."
C# program that uses Remove, RemoveAt on List
using System; using System.Collections.Generic; class Program { static void Main[] { // Step 1: create List. List values = new List[]; values.Add["AA"]; values.Add["BB"]; values.Add["CC"]; // Step 2: remove by value. values.Remove["BB"]; Console.WriteLine[string.Join[";", values]]; // Step 3: remove by index. values.RemoveAt[1]; Console.WriteLine[string.Join[";", values]]; } }AA;CC AARemoveRange. This can remove elements in a certain series of indexes. One useful way to use this method is to remove the first or last several elements at once.
Next We remove all elements except the last two. The code is robust because it uses Math.Max to avoid negative parameters.
Math.Max, Min
C# program that uses RemoveRange method
using System; using System.Collections.Generic; class Program { static void Main[] { List list = new List[]; list.Add[1]; list.Add[2]; list.Add[3]; list.Add[4]; list.Add[5]; // Remove all except last 2 int remove = Math.Max[0, list.Count - 2]; list.RemoveRange[0, remove]; foreach [int i in list] { Console.Write[i]; } } }45RemoveRange, example 2. Here we use RemoveRange to remove the first N elements in a List. We also use Math.Min here to avoid arguments that are too large and would raise an exception.
C# program that uses RemoveRange on first elements
using System; using System.Collections.Generic; class Program { static void Main[] { List list = new List[]; list.Add[1]; list.Add[2]; list.Add[3]; list.Add[4]; list.Add[5]; // Remove first 2 elements int remove = Math.Min[list.Count, 2]; list.RemoveRange[0, remove]; foreach [int i in list] { Console.Write[i]; } } }345RemoveAt. The RemoveAt[] method removes one element. How is this method on the List type implemented in .NET? It requires an index argument.
Example In this program we specify that a List be instantiated with three strings [the words in the name of this website].
Next We remove the string at index 1, which is the second string. The List now contains only two strings: "dot" and "perls."
Var
String Literal
C# program that uses RemoveAt
using System; using System.Collections.Generic; class Program { static void Main[] { var list = new List[]; list.Add["dot"]; list.Add["net"]; list.Add["perls"]; list.RemoveAt[1]; foreach [string element in list] { Console.WriteLine[element]; } } }dot perlsNotes, performance. Methods on List that remove elements require linear time. It could be faster to assign null to elements you want to erase, rather than removing them.
Note RemoveAt is faster than Remove. It doesn't need to iterate through the number of elements equal to index.
RemoveAll You can use RemoveAll to remove all elements in the List that match a certain predicate expression.
Tip It is often easiest to use the lambda expression syntax with the RemoveAll method, which can reduce line count.
RemoveAll
Discussion. When you call RemoveAt, all the element following the index you remove will be copied and shifted forward. This is not efficient.
However If you want to remove an element but eliminate copying, you could simply assign it to null or a default[] expression.
Null
Default
Also The Insert method on List suffers from a similar performance drawback. It causes excessive element copying.
List Insert
A review. We invoked the Remove, RemoveAt, RemoveAll and RemoveRange methods. We found out how to remove the first and last elements, and reviewed algorithmic complexity.
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Lists are containers used in C++ to store data in a non contiguous fashion, Normally, Arrays and Vectors are contiguous in nature, therefore the insertion and deletion operations are costlier as compared to the insertion and deletion option in Lists.
list::remove[]
remove[] function is used to remove all the values from the list that correspond to the value given as parameter to the function
Syntax :
Examples:
Errors and Exceptions
- Shows error if the value passed doesn’t match the list type.
- Shows no exception throw guarantee if the comparison between value and elements of the list feature doesn’t throw any exception.
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list mylist{ 1, 2, 2, 2, 5, 6, 7 }; for [auto it = mylist.begin[]; it != mylist.end[]; ++it] |
Output:
list::remove_if[]
remove_if[] function is used to remove all the values from the list that correspond true to the predicate or condition given as parameter to the function. The function iterates through every member of the list container and removes all the element that return true for the predicate.
Syntax :
Examples:
Errors and Exceptions
- Shows no exception throw guarantee if the predicate function feature doesn’t throw any exception.
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bool even[const int& value] { return [value % 2] == 0; } list mylist{ 1, 2, 2, 2, 5, 6, 7 }; for [auto it = mylist.begin[]; it != mylist.end[]; ++it] |
Output:
Application : Given a list of integers, remove all the prime numbers from the list and print the list.
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bool prime[const int& value] for [i = 2; i < value; i++] { list mylist{ 2, 4, 6, 7, 9, 11, 13 }; for [auto it = mylist.begin[]; it != mylist.end[]; ++it] |
Output:
Article Tags :
The list::remove[] is a built-in function in C++ STL which is used to remove elements from a list container. It removes elements comparing to a value. It takes a value as the parameter and removes all the elements from the list container whose value is equal to the value passed in the parameter of the function.
Syntax:
list_name.remove[val]Parameters: This function accepts a single parameter val which refers to the value of elements needed to be removed from the list. The remove[] function will remove all the elements from the list whose value is equal to val.
Return Value: This function does not returns any value.
Below program illustrates the list::remove[] function.
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#include using namespace std; int main[] { list demoList; demoList.push_back[10]; demoList.push_back[20]; demoList.push_back[20]; demoList.push_back[30]; demoList.push_back[40]; cout Chủ Đề |