To add or append an element to the list in R use append() function. This function takes 3 parameters input list, the string or list you wanted to append, and position.
The list.append() function from the rlist package can also use to append one list with another in R.
1. Quick Examples of Add element to List
Following are quick examples of how to add or append elements to the list in R.
# Quick examples
# Using R base append()
li = list('java','python')
li2 <- append(li,'r')
print(li2)
# Add element to list at specified position
li = list('java','python')
li2 <- append(li,'r',after=1)
print(li2)
# Using list.append()
library('rlist')
li2 <- list.append(li,'r')
print(li2)
# Named List
library('rlist')
li = list(id=11,name='python')
li2 <- list.append(li,pages=34)
print(li2)
# Append list with another list
li = list('java','python')
li2 = list('r','php')
li3 <- append(li,li2)
print(li3)
2. R Base append() Syntax
Following is the syntax of the R base append() function
# Syntax of append()
append(x, values, after = length(x))
Parameters
x– Input listvalues– string, list or vector.after– Position to add. Optional. When not specified the element is added at the end of the list.
3. Append Element to List
By using the append() function let’s add an element to the existing list in R. By default, it adds an element at the end of the list. The following example adds an element r to the list.
# Add element to list
li = list('java','python')
li2 <- append(li,'r')
print(li2)
Yields below output. Note that we have added item r to the list.
# Output
[[1]]
[1] "java"
[[2]]
[1] "python"
[[3]]
[1] "r"
4. Add Element to List at Specified Position
Use the after parameter to specify the position where you wanted to add the element. The following example adds elements after the first position.
# Add element to list at specified position
li = list('java','python')
li2 <- append(li,'r',after=1)
print(li2)
Yields below output
# Output
[[1]]
[1] "java"
[[2]]
[1] "r"
[[3]]
[1] "python"
5. Add Multiple Elements to List
Package rlist provides a list.append() function to add multiple elements to the list in R. In order to use this function first, you need to install R package by using install.packages("rlist") and load it using the library("rlist").
# Add multiple elements to list
library('rlist')
li2 <- list.append(li,'r','50')
print(li2)
Yields below output.
# Output
[[1]]
[1] "java"
[[2]]
[1] "python"
[[3]]
[1] "r"
[[4]]
[1] "50"
Using this function we can also append elements to the named list.
# Named List
library('rlist')
li = list(id=11,name='python')
li2 <- list.append(li,pages=34)
print(li2)
6. Append List with Another List
To append one list with another list pass both lists to the append() function, this adds a second list to the end of the first list and returns a single list.
# Append list with another list
li = list('java','python')
li2 = list('r','php')
li3 <- append(li,li2)
print(li3)
7. Using c() to Append List
If you are not aware c() is a combined function that is used to merge the list, vector e.t.c. The following example uses c() to append two lists.
# using c()
li3 = c(li,li2)
print(li3)
Conclusion
In this article, you have learned how to add or append an element to the list by using R base append(), list.append() from the rlist package. You can find the complete example from this article at Github R Programming Examples Project.
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