Extracting List Elements
Good. Now let's find out how to extract certain elements of a list. The indexing of lists is the same as the indexing of vectors, i.e., the first element has index 1, the second has index 2, and so on. For example, let's extract the second element of the test list from the previous chapter.
1234# Creating a list test <- list(text = "Text", number = 42, logical = TRUE) # Extracting the second element test[2]
As you might notice, we extracted the element of list as list itself! It follows that for the example above, you can not perform any arithmetical operations with the extracted element since it is a list, not a number. To output an element from the list with its type, place its index inside double square brackets. For the example above, this will look like this:
123test <- list(text = "Text", number = 42, logical = TRUE) # Extract the second element as numerical test[[2]]
If the list has namings, you can use the dollar $ sign to access the value with its type straightaway.
Also, you can pass the element's name to access its value within both single or double square brackets (like, test$text, test['text'], or test[['text']]).
Swipe to start coding
Given list info from the previous chapter. You need to complete the following tasks:
- Extract the first element as a list.
- Output class of the element from task 1 using
class()function. - Extract the fourth element as a numeric type.
- Output class of the element from task 3 using
class()function.
Lösung
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Can you explain the difference between using single and double square brackets with lists in R?
How do I extract multiple elements from a list at once?
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Good. Now let's find out how to extract certain elements of a list. The indexing of lists is the same as the indexing of vectors, i.e., the first element has index 1, the second has index 2, and so on. For example, let's extract the second element of the test list from the previous chapter.
1234# Creating a list test <- list(text = "Text", number = 42, logical = TRUE) # Extracting the second element test[2]
As you might notice, we extracted the element of list as list itself! It follows that for the example above, you can not perform any arithmetical operations with the extracted element since it is a list, not a number. To output an element from the list with its type, place its index inside double square brackets. For the example above, this will look like this:
123test <- list(text = "Text", number = 42, logical = TRUE) # Extract the second element as numerical test[[2]]
If the list has namings, you can use the dollar $ sign to access the value with its type straightaway.
Also, you can pass the element's name to access its value within both single or double square brackets (like, test$text, test['text'], or test[['text']]).
Swipe to start coding
Given list info from the previous chapter. You need to complete the following tasks:
- Extract the first element as a list.
- Output class of the element from task 1 using
class()function. - Extract the fourth element as a numeric type.
- Output class of the element from task 3 using
class()function.
Lösung
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