Online Test Banks
Score higher
See Online Test Banks
Learning anything is easy
Browse Online Courses
Mobile Apps
Learning on the go
Explore Mobile Apps
Dummies Store
Shop for books and more
Start Shopping

How to Create Subsets of Your Data in R

Often the first task in data processing is to create subsets of your data in R for further analysis. You’re already familiar with the three subset operators:

  • $: The dollar-sign operator selects a single element of your data (and drops the dimensions of the returned object). When you use this operator with a data frame, the result is always a vector; when you use it with a named list, you get that element.

  • [[: The double-square-brackets operator also returns a single element, but it offers you the flexibility of referring to the elements by position, rather than by name. You use it for data frames and lists.

  • [: The single-square-brackets operator can return multiple elements of your data.

This summary is simplified.

When you use the single-square-brackets operator, you return multiple elements of your data. This means that you need a way of specifying exactly which elements you need.

In this paragraph, you can try subsetting with the built-in dataset islands, a named numeric vector with 48 elements.

> str(islands)
 Named num [1:48] 11506 5500 16988 2968 16 ...
 - attr(*, "names")= chr [1:48] "Africa" "Antarctica" "Asia" "Australia" ...
Subset Effect Example
Blank Returns all your data islands[]
Positive numerical values Extracts the elements at these locations islands[c(8, 1, 1, 42)]
Negative numerical values Extract all but these elements; in other words, excludes these elements islands[-(3:46)]
Logical values A logical value of TRUE includes element; FALSE excludes element islands[islands < 20]
Text strings Includes elements where the names match islands[c("Madagascar", "Cuba")]
  • Add a Comment
  • Print
  • Share
blog comments powered by Disqus

Inside Sweepstakes

Win $500. Easy.