In R, you can use indexing operators to access, modify, or extract elements from a list. R has main 3 indexing operators. They are as follows :
- [ ] always returns a list with a single element.
- [[ ]] returns a object of the class of item contained in the list.
- $ returns elements from list that have names associated with it, not necessarily same class
Examples: Extracting Elements from List
To access a specific element in a list, you can use the [ ] operator with the index of the element you want to extract. The first element has an index of 1. It returns data in the form of list.
dat <- list( str='R', vec=c(1,2,3), bool=TRUE ) a = dat["str"]
class(a) returns "list". It means "a" is a list.
b = dat[["str"]]
class(b) returns "character". It means "b" is a character vector.
c = dat$str
class(c) returns "character". It means "c" is a character vector.
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| R Indexing Operators |
Both $ and [[ ]] works same. But it is advisable to use [[ ]] in functions and loops.
How to Extract Multiple Elements from List
You can extract multiple elements from the list using a vector of indices within the [ ] operator.
# Creating a list
my_list <- list("apple", "banana", "orange", "grape")
# Extracting elements at index 1 and 3
selected_elements <- my_list[c(1, 3)]
print(selected_elements)
Output:
[[1]] [1] "apple" [[2]] [1] "orange"
How to Modify Elements in a List
You can also use indexing operators to modify elements within a list.
# Creating a list
my_list <- list("apple", "banana", "orange", "grape")
# Modifying the element at index 2
my_list[2] <- "pear"
print(my_list)
Output:
[[1]] [1] "apple" [[2]] [1] "pear" [[3]] [1] "orange" [[4]] [1] "grape
How to extract a list of list
dat1 <- list(
Bal02 = list(
ivtable = data.frame(x=1, y=2, z=3),
ivscore = 0.1
)
)
dat1$Bal02$ivtable
dat1$Bal02: This part of the code extracts the element with the name "Bal02" from the list dat1. It assumes that dat1 is a list, and within that list, there is an element named "Bal02", which is also a list.
$ivtable: After extracting the sublist "Bal02" using $Bal02, we further extract the element "ivtable" from this sublist using the $ operator. It assumes that the sublist "Bal02" contains an element named "ivtable".
You can also use the following command to extract a list of lists (sublist) in R.
dat1[[c("Bal02","ivtable")]]
Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. He has over 10 years of experience in data science. During his tenure, he worked with global clients in various domains like Banking, Insurance, Private Equity, Telecom and HR.
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