R中的列表是一个由有序的对象集合组成的通用对象。列表是一维的、异质的数据结构。列表可以是一个向量的列表，一个矩阵的列表，一个字符的列表和一个函数的列表，等等。
列表是一个向量，但有异质的数据元素。R中的列表是通过使用 list() 函数来创建的。R允许通过使用索引值来访问列表中的元素。在 R 中，列表的索引从 1 开始，而不是像其他编程语言那样从 0 开始。
创建一个列表要在R中创建一个列表，你需要使用名为 “list() “的函数。换句话说，一个列表是一个包含其他对象的通用向量。为了说明列表的样子，我们在这里举一个例子。我们想建立一个带有细节的雇员列表。因此，我们希望得到诸如ID、雇员姓名和雇员人数等属性。
例子
# R program to create a List # The first attributes is a numeric vector# containing the employee IDs which is created# using the command hereempId = c(1, 2, 3, 4) # The second attribute is the employee name# which is created using this line of code here# which is the character vectorempName = c("Debi", "Sandeep", "Subham", "Shiba") # The third attribute is the number of employees# which is a single numeric variable.numberOfEmp = 4 # We can combine all these three different# data types into a list# containing the details of employees# which can be done using a list commandempList = list(empId, empName, numberOfEmp) print(empList)输出
[[1]][1] 1 2 3 4[[2]][1] "Debi" "Sandeep" "Subham" "Shiba" [[3]][1] 4访问列表中的组件我们可以通过两种方式访问列表中的组件。
通过名字访问组件： 一个列表中的所有组件都可以被命名，我们可以用这些名字来访问列表中的组件，使用 dollar 命令。例子
# R program to access# components of a list # Creating a list by naming all its componentsempId = c(1, 2, 3, 4)empName = c("Debi", "Sandeep", "Subham", "Shiba")numberOfEmp = 4empList = list( "ID" = empId, "Names" = empName, "Total Staff" = numberOfEmp )print(empList) # Accessing components by namescat("Accessing name components using command ")print(empListNames)输出
$ID[1] 1 2 3 4$Names[1] "Debi" "Sandeep" "Subham" "Shiba" $`Total Staff`[1] 4Accessing name components using $ command[1] "Debi" "Sandeep" "Subham" "Shiba" 通过索引访问组件： 我们也可以使用索引来访问列表的组件。要访问列表的顶层组件，我们必须使用双切分运算符”[ []]” ，也就是两个方括号，如果我们想访问列表的低层或内层组件，我们必须使用另一个方括号 “[]” 和双切分运算符”[[ ] “。例子
# R program to access# components of a list # Creating a list by naming all its componentsempId = c(1, 2, 3, 4)empName = c("Debi", "Sandeep", "Subham", "Shiba")numberOfEmp = 4empList = list( "ID" = empId, "Names" = empName, "Total Staff" = numberOfEmp )print(empList) # Accessing a top level components by indicescat("Accessing name components using indices ")print(empList[[2]]) # Accessing a inner level components by indicescat("Accessing Sandeep from name using indices ")print(empList[[2]][2]) # Accessing another inner level components by indicescat("Accessing 4 from ID using indices ")print(empList[[1]][4])输出
$ID[1] 1 2 3 4$Names[1] "Debi" "Sandeep" "Subham" "Shiba" $`Total Staff`[1] 4Accessing name components using indices[1] "Debi" "Sandeep" "Subham" "Shiba" Accessing Sandeep from name using indices[1] "Sandeep"Accessing 4 from ID using indices[1] 4修改列表中的组件列表也可以通过访问组件并将其替换为你想要的组件来进行修改。
例子
# R program to edit# components of a list # Creating a list by naming all its componentsempId = c(1, 2, 3, 4)empName = c("Debi", "Sandeep", "Subham", "Shiba")numberOfEmp = 4empList = list( "ID" = empId, "Names" = empName, "Total Staff" = numberOfEmp)cat("Before modifying the list ")print(empList) # Modifying the top-level componentempList$`Total Staff` = 5 # Modifying inner level componentempList[[1]][5] = 5empList[[2]][5] = "Kamala" cat("After modified the list ")print(empList)输出
Before modifying the listID[1] 1 2 3 4Names[1] "Debi" "Sandeep" "Subham" "Shiba" `Total Staff`[1] 4After modified the listID[1] 1 2 3 4 5Names[1] "Debi" "Sandeep" "Subham" "Shiba" "Kamala"`Total Staff`[1] 5列表的连接两个列表可以使用连接函数进行连接。因此，当我们要连接两个列表时，必须使用连接运算符。
语法
list = c(list, list1)
list = 原始列表
list1 = 新列表
例子
# R program to edit# components of a list # Creating a list by naming all its componentsempId = c(1, 2, 3, 4)empName = c("Debi", "Sandeep", "Subham", "Shiba")numberOfEmp = 4empList = list( "ID" = empId, "Names" = empName, "Total Staff" = numberOfEmp)cat("Before concatenation of the new list ")print(empList) # Creating another listempAge = c(34, 23, 18, 45)empAgeList = list( "Age" = empAge) # Concatenation of list using concatenation operatorempList = c(empList, empAgeList) cat("After concatenation of the new list ")print(empList)输出
Before concatenation of the new listID[1] 1 2 3 4Names[1] "Debi" "Sandeep" "Subham" "Shiba" `Total Staff`[1] 4After concatenation of the new listID[1] 1 2 3 4Names[1] "Debi" "Sandeep" "Subham" "Shiba"`Total Staff`[1] 4$Age[1] 34 23 18 45删除列表中的组件要删除列表中的组件，首先，我们需要访问这些组件，然后在这些组件前插入一个负号。它表示我们必须删除该组件。
例子
# R program to access# components of a list # Creating a list by naming all its componentsempId = c(1, 2, 3, 4)empName = c("Debi", "Sandeep", "Subham", "Shiba")numberOfEmp = 4empList = list( "ID" = empId, "Names" = empName, "Total Staff" = numberOfEmp)cat("Before deletion the list is ")print(empList) # Deleting a top level componentscat("After Deleting Total staff components ")print(empList[-3]) # Deleting a inner level componentscat("After Deleting sandeep from name ")print(empList[[2]][-2])输出
Before deletion the list isID[1] 1 2 3 4Names[1] "Debi" "Sandeep" "Subham" "Shiba" `Total Staff`[1] 4After Deleting Total staff componentsID[1] 1 2 3 4$Names[1] "Debi" "Sandeep" "Subham" "Shiba" After Deleting sandeep from name[1] "Debi" "Subham" "Shiba" 合并列表我们可以通过将所有的列表放入一个单一的列表来合并列表。
# Create two lists.lst1