as.list[] function in R Programming Language is used to convert an object to a list. These objects can be Vectors, Matrices, Factors, and dataframes.
Syntax: as.list[object]
Parameters:
object: Vector, Matrix, factor, or data frame
R – as.list[] Function Example
Example 1: Converting Vector to list using as.list[] function in R Language
Output:
[[1]]
[1] 1
[[2]]
[1] 2
[[3]]
[1] 3
[[4]]
[1] 4
[[5]]
[1] 5
Example 2: Converting data frame to list using as.list[] function in R Language
Output:
Time demand
1 1 8.3
2 2 10.3
3 3 19.0
4 4 16.0
5 5 15.6
6 7 19.8
$Time
[1] 1 2 3 4 5 7
$demand
[1] 8.3 10.3 19.0 16.0 15.6 19.8
attr[, "reference"]
[1] "A1.4, p. 270"
Example 3: Converting matrix to list using as.list[] function in R Language
|
c[1, 2, 3, 4, 5, 6, 7, 8, 9],
rownames[A] = c["a", "b", "c"]
colnames[A] = c["c", "d", "e"]
|
Output:
The 3x3 matrix:
c d e
a 1 2 3
b 4 5 6
c 7 8 9
[[1]]
[1] 1
[[2]]
[1] 4
[[3]]
[1] 7
[[4]]
[1] 2
[[5]]
[1] 5
[[6]]
[1] 8
[[7]]
[1] 3
[[8]]
[1] 6
[[9]]
[1] 9
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Collections.singletonList[object] method returns an immutable list containing only the specified object. The returned list is serializable.
//Assuming that your object is a valid List object, you can use: Collections.singletonList[object] -- Returns an immutable list containing only the specified object.
List list = Collections.singletonList[object];
Stream.collect[Collectors.toList[]] can be used to collect Stream elements into a list. We can leverage this to convert object to a list.
//If you want it in a specific datatype, use Stream.of[object]:
List list = Stream.of[object].map[Object::toString].collect[Collectors.toList[]]
//Similarly, you can change the method in the map to convert to the datatype you need.
//Example
// Accumulate names into a List
List list = people.stream[].map[Person::getName].collect[Collectors.toList[]];
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public:
T Find[Predicate ^ match]; public T Find [Predicate match]; public T? Find [Predicate match]; member this.Find : Predicate x.PartName.Contains["seat"]]];
// Check if an item with Id 1444 exists.
Console.WriteLine["\nExists: Part with Id=1444: {0}",
parts.Exists[x => x.PartId == 1444]];
/*This code example produces the following output:
ID: 1234 Name: crank arm
ID: 1334 Name: chain ring
ID: 1434 Name: regular seat
ID: 1444 Name: banana seat
ID: 1534 Name: cassette
ID: 1634 Name: shift lever
Contains: Part with Id=1734: False
Find: Part where name contains "seat": ID: 1434 Name: regular seat
Exists: Part with Id=1444: True
*/
}
}
Imports System.Collections.Generic
' Simple business object. A PartId is used to identify a part
' but the part name can change.
Public Class Part
Implements IEquatable[Of Part]
Public Property PartName[] As String
Get
Return m_PartName
End Get
Set[value As String]
m_PartName = Value
End Set
End Property
Private m_PartName As String
Public Property PartId[] As Integer
Get
Return m_PartId
End Get
Set[value As Integer]
m_PartId = Value
End Set
End Property
Private m_PartId As Integer
Public Overrides Function ToString[] As String
Return Convert.ToString["ID: " & PartId & " Name: "] & PartName
End Function
Public Overrides Function Equals[obj As Object] As Boolean
If obj Is Nothing Then
Return False
End If
Dim objAsPart As Part = TryCast[obj, Part]
If objAsPart Is Nothing Then
Return False
Else
Return Equals[objAsPart]
End If
End Function
Public Overrides Function GetHashCode[] As Integer
Return PartId
End Function
Public Overloads Function Equals[other As Part] As Boolean _
Implements IEquatable[Of Part].Equals
If other Is Nothing Then
Return False
End If
Return [Me.PartId.Equals[other.PartId]]
End Function
' Should also override == and != operators.
End Class
Public Class Example
Public Shared Sub Main[]
' Create a list of parts.
Dim parts As New List[Of Part][]
' Add parts to the list.
parts.Add[New Part[] With { _
.PartName = "crank arm", _
.PartId = 1234 _
}]
parts.Add[New Part[] With { _
.PartName = "chain ring", _
.PartId = 1334 _
}]
parts.Add[New Part[] With { _
.PartName = "regular seat", _
.PartId = 1434 _
}]
parts.Add[New Part[] With { _
.PartName = "banana seat", _
.PartId = 1444 _
}]
parts.Add[New Part[] With { _
.PartName = "cassette", _
.PartId = 1534 _
}]
parts.Add[New Part[] With { _
.PartName = "shift lever", _
.PartId = 1634 _
}]
' Write out the parts in the list. This will call the overridden ToString method
' in the Part class.
Console.WriteLine[]
For Each aPart As Part In parts
Console.WriteLine[aPart]
Next
' Check the list for part #1734. This calls the IEquatable.Equals method
' of the Part class, which checks the PartId for equality.
Console.WriteLine[vbLf & "Contains: Part with Id=1734: {0}",
parts.Contains[New Part[] With { _
.PartId = 1734, _
.PartName = "" _
}]]
' Find items where name contains "seat".
Console.WriteLine[vbLf & "Find: Part where name contains ""seat"": {0}",
parts.Find[Function[x] x.PartName.Contains["seat"]]]
' Check if an item with Id 1444 exists.
Console.WriteLine[vbLf & "Exists: Part with Id=1444: {0}",
parts.Exists[Function[x] x.PartId = 1444]]
'This code example produces the following output:
'
' ID: 1234 Name: crank arm
' ID: 1334 Name: chain ring
' ID: 1434 Name: regular seat
' ID: 1444 Name: banana seat
' ID: 1534 Name: cassette
' ID: 1634 Name: shift lever
'
' Contains: Part with Id=1734: False
'
' Find: Part where name contains "seat": ID: 1434 Name: regular seat
'
' Exists: Part with Id=1444: True
'
End Sub
End Class
The following example demonstrates the find methods for the List class. The example for the List class contains book objects, of class Book, using the data from the Sample XML File: Books [LINQ to XML]. The FillList method in the example uses LINQ to XML to parse the values from the XML to property values of the book objects.
The following table describes the examples provided for the find methods.
Method
Example
| Find[Predicate] |
Finds a book by an ID using the IDToFind predicate delegate. C# example uses an anonymous delegate. |
| FindAll[Predicate] |
Find all books that whose Genre property is "Computer" using the FindComputer predicate delegate. |
| FindLast[Predicate] |
Finds the last book in the collection that has a publish date before 2001, using the PubBefore2001 predicate delegate. C# example uses an anonymous delegate. |
| FindIndex[Predicate] |
Finds the index of first computer book using the FindComputer predicate delegate. |
| FindLastIndex[Predicate] |
Finds the index of the last computer book using the FindComputer predicate delegate. |
| FindIndex[Int32, Int32, Predicate] |
Finds the index of first computer book in the second half of the collection, using the FindComputer predicate delegate. |
| FindLastIndex[Int32, Int32, Predicate] |
Finds the index of last computer book in the second half of the collection, using the FindComputer predicate delegate. |
using System;
using System.Collections.Generic;
using System.Linq;
using System.Xml.Linq;
namespace Find
{
class Program
{
private static string IDtoFind = "bk109";
private static List Books = new List[];
public static void Main[string[] args]
{
FillList[];
// Find a book by its ID.
Book result = Books.Find[
delegate[Book bk]
{
return bk.ID == IDtoFind;
}
];
if [result != null]
{
DisplayResult[result, "Find by ID: " + IDtoFind];
}
else
{
Console.WriteLine["\nNot found: {0}", IDtoFind];
}
// Find last book in collection published before 2001.
result = Books.FindLast[
delegate[Book bk]
{
DateTime year2001 = new DateTime[2001,01,01];
return bk.Publish_date < year2001;
}];
if [result != null]
{
DisplayResult[result, "Last book in collection published before 2001:"];
}
else
{
Console.WriteLine["\nNot found: {0}", IDtoFind];
}
// Find all computer books.
List results = Books.FindAll[FindComputer];
if [results.Count != 0]
{
DisplayResults[results, "All computer:"];
}
else
{
Console.WriteLine["\nNo books found."];
}
// Find all books under $10.00.
results = Books.FindAll[
delegate[Book bk]
{
return bk.Price < 10.00;
}
];
if [results.Count != 0]
{
DisplayResults[results, "Books under $10:"];
}
else
{
Console.WriteLine["\nNo books found."];
}
// Find index values.
Console.WriteLine[];
int ndx = Books.FindIndex[FindComputer];
Console.WriteLine["Index of first computer book: {0}", ndx];
ndx = Books.FindLastIndex[FindComputer];
Console.WriteLine["Index of last computer book: {0}", ndx];
int mid = Books.Count / 2;
ndx = Books.FindIndex[mid, mid, FindComputer];
Console.WriteLine["Index of first computer book in the second half of the collection: {0}", ndx];
ndx = Books.FindLastIndex[Books.Count - 1, mid, FindComputer];
Console.WriteLine["Index of last computer book in the second half of the collection: {0}", ndx];
}
// Populates the list with sample data.
private static void FillList[]
{
// Create XML elements from a source file.
XElement xTree = XElement.Load[@"c:\temp\books.xml"];
// Create an enumerable collection of the elements.
IEnumerable elements = xTree.Elements[];
// Evaluate each element and set set values in the book object.
foreach [XElement el in elements]
{
Book book = new Book[];
book.ID = el.Attribute["id"].Value;
IEnumerable props = el.Elements[];
foreach [XElement p in props]
{
if [p.Name.ToString[].ToLower[] == "author"]
{
book.Author = p.Value;
}
else if [p.Name.ToString[].ToLower[] == "title"]
{
book.Title = p.Value;
}
else if [p.Name.ToString[].ToLower[] == "genre"]
{
book.Genre = p.Value;
}
else if [p.Name.ToString[].ToLower[] == "price"]
{
book.Price = Convert.ToDouble[p.Value];
}
else if [p.Name.ToString[].ToLower[] == "publish_date"]
{
book.Publish_date = Convert.ToDateTime[p.Value];
}
else if [p.Name.ToString[].ToLower[] == "description"]
{
book.Description = p.Value;
}
}
Books.Add[book];
}
DisplayResults[Books, "All books:"];
}
// Explicit predicate delegate.
private static bool FindComputer[Book bk]
{
if [bk.Genre == "Computer"]
{
return true;
}
else
{
return false;
}
}
private static void DisplayResult[Book result, string title]
{
Console.WriteLine[];
Console.WriteLine[title];
Console.WriteLine["\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", result.ID,
result.Author, result.Title, result.Genre, result.Price,
result.Publish_date.ToShortDateString[]];
Console.WriteLine[];
}
private static void DisplayResults[List results, string title]
{
Console.WriteLine[];
Console.WriteLine[title];
foreach [Book b in results]
{
Console.Write["\n{0}\t{1}\t{2}\t{3}\t{4}\t{5}", b.ID,
b.Author, b.Title, b.Genre, b.Price,
b.Publish_date.ToShortDateString[]];
}
Console.WriteLine[];
}
}
public class Book
{
public string ID { get; set; }
public string Author { get; set; }
public string Title { get; set; }
public string Genre { get; set; }
public double Price { get; set; }
public DateTime Publish_date { get; set; }
public string Description { get; set; }
}
}
Imports System.Collections.Generic
Imports System.Linq
Imports System.Xml.Linq
Module Module1
Private IDToFind As String = "bk109"
Public Books As New List[Of Book]
Sub Main[]
FillList[]
' Find a book by its ID.
Dim result As Book = Books.Find[AddressOf FindID]
If result IsNot Nothing Then
DisplayResult[result, "Find by ID: " & IDToFind]
Else
Console.WriteLine[vbCrLf & "Not found: " & IDToFind]
End If
Console.WriteLine[]
' Find last book in collection that has a publish date before 2001.
result = Books.FindLast[AddressOf PubBefore2001]
If result IsNot Nothing Then
DisplayResult[result, "Last book in collection published before 2001:"]
Else
Console.WriteLine[vbCrLf & "Not found: " & IDToFind]
End If
Console.WriteLine[]
' Find all computer books.
Dim results As List[Of Book] = Books.FindAll[AddressOf FindComputer]
If results.Count 0 Then
DisplayResults[results, "All computer books:"]
Else
Console.WriteLine[vbCrLf & "No books found."]
End If
Console.WriteLine[]
' Find all books under $10.00.
results = Books.FindAll[AddressOf FindUnderTen]
If results.Count 0 Then
DisplayResults[results, "Books under $10:"]
Else
Console.WriteLine[vbCrLf & "No books found."]
End If
Console.WriteLine[]
' Find index values.
Console.WriteLine[]
Dim ndx As Integer = Books.FindIndex[AddressOf FindComputer]
Console.WriteLine["Index of first computer book: " & ndx]
ndx = Books.FindLastIndex[AddressOf FindComputer]
Console.WriteLine["Index of last computer book: " & ndx]
Dim mid As Integer = Books.Count / 2
ndx = Books.FindIndex[mid, mid, AddressOf FindComputer]
Console.WriteLine["Index of first computer book in the second half of the collection: " & ndx]
ndx = Books.FindLastIndex[Books.Count - 1, mid, AddressOf FindComputer]
Console.WriteLine["Index of last computer book in the second half of the collection: " & ndx]
End Sub
Private Sub FillList[]
' Create XML elements from a source file.
Dim xTree As XElement = XElement.Load["c:\temp\books.xml"]
' Create an enumerable collection of the elements.
Dim elements As IEnumerable[Of XElement] = xTree.Elements
' Evaluate each element and set values in the book object.
For Each el As XElement In elements
Dim Book As New Book[]
Book.ID = el.Attribute["id"].Value
Dim props As IEnumerable[Of XElement] = el.Elements
For Each p As XElement In props
If p.Name.ToString.ToLower = "author" Then
Book.Author = p.Value
End If
If p.Name.ToString.ToLower = "title" Then
Book.Title = p.Value
End If
If p.Name.ToString.ToLower = "genre" Then
Book.Genre = p.Value
End If
If p.Name.ToString.ToLower = "price" Then
Book.Price = Convert.ToDouble[p.Value]
End If
If p.Name.ToString.ToLower = "publish_date" Then
Book.Publish_date = Convert.ToDateTime[p.Value]
End If
If p.Name.ToString.ToLower = "description" Then
Book.Description = p.Value
End If
Next
Books.Add[Book]
Next
DisplayResults[Books, "All books:"]
Console.WriteLine[]
End Sub
' Predicate delegates for
' Find and FindAll methods.
Private Function FindID[ByVal bk As Book] As Boolean
If bk.ID = IDToFind Then
Return True
Else
Return False
End If
End Function
Private Function FindComputer[ByVal bk As Book] As Boolean
If bk.Genre = "Computer" Then
Return True
Else
Return False
End If
End Function
Private Function FindUnderTen[ByVal bk As Book] As Boolean
Dim tendollars As Double = 10.0
If bk.Price < tendollars Then
Return True
Else
Return False
End If
End Function
Private Function PubBefore2001[ByVal bk As Book] As Boolean
Dim year2001 As DateTime = New DateTime[2001, 1, 1]
Return bk.Publish_date < year2001
End Function
Private Sub DisplayResult[ByVal result As Book, ByVal title As String]
Console.WriteLine[]
Console.WriteLine[title]
Console.WriteLine[vbLf & result.ID & vbTab & result.Author & _
vbTab & result.Title & vbTab & result.Genre & _
vbTab & result.Publish_date & vbTab & result.Price]
Console.WriteLine[]
End Sub
Private Sub DisplayResults[ByVal results As List[Of Book], ByVal title As String]
Console.WriteLine[]
Console.WriteLine[title]
For Each b As Book In results
Console.Write[vbLf & b.ID & vbTab & b.Author & _
vbTab & b.Title & vbTab & b.Genre & _
vbTab & b.Publish_date & vbTab & b.Price]
Next
Console.WriteLine[]
End Sub
Public Class Book
Public ID As String
Public Author As String
Public Title As String
Public Genre As String
Public Price As Double
Public Publish_date As DateTime
Public Description As String
End Class
End Module
Remarks
The Predicate is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of the current List are individually passed to the Predicate delegate, moving forward in the List, starting with the first element and ending with the last element. Processing is stopped when a match is found.
Important
When searching a list containing value types, make sure the default value for the type does not satisfy the search predicate. Otherwise, there is no way to distinguish between a default value indicating that no match was found and a list element that happens to have the default value for the type. If the default value satisfies the search predicate, use the FindIndex method instead.
This method performs a linear search; therefore, this method is an O[n] operation, where n is Count.
Applies to
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