The ls() Function in R
Basic Usage
The ls() function retrieves the names of objects in a given environment. By default, it lists objects in the global environment.
# Define some variables a <- 1 b <- 2 c <- 3 # List objects in the global environment ls() # Returns "a" "b" "c"
Arguments of ls()
- name: Specifies the environment from which to list objects. By default, ls() uses the global environment.
# List objects in a specific environment
my_env <- new.env()
assign("x", 10, envir = my_env)
ls(envir = my_env) # Returns "x"
- pattern: A regular expression to filter the names of objects. Only objects with names matching the pattern are returned.
# Define more variables apple <- 1 orange <- 2 # List objects with names containing "ap" ls(pattern = "ap") # Returns "apple"
- all.names: Logical value indicating whether to include objects starting with a dot (hidden objects). The default is FALSE.
# Define a hidden variable .hidden <- 100 # List objects including hidden ones ls(all.names = TRUE) # Returns ".hidden" "a" "b" "c"
Environments and ls()
ls() can be used to list objects in different environments, not just the global environment.
# Create a new environment
my_env <- new.env()
assign("foo", 42, envir = my_env)
assign("bar", 99, envir = my_env)
# List objects in the new environment
ls(envir = my_env) # Returns "foo" "bar"
Using ls() with Packages
You can also use ls() to list objects in the environments of packages that are currently loaded.
# Load the dplyr package
library(dplyr)
# List objects in the dplyr package environment
ls("package:dplyr") # Lists functions and objects in the dplyr package
Examples
Listing Objects in a Specific Environment
# Define a new environment local_env <- new.env() local_env$a <- 1 local_env$b <- 2 # List objects in the local environment ls(envir = local_env) # Returns "a" "b"
Filtering Object Names
# Define variables data1 <- 10 data2 <- 20 other <- 30 # List objects whose names start with "data" ls(pattern = "^data") # Returns "data1" "data2"
Practical Use Cases
- Debugging: Quickly identify which objects are available in the current environment or a specific environment.
- Package Exploration: Explore functions and datasets within a loaded package.
- Clean-up: Determine which objects are present before performing environment clean-up.
Summary
- Basic Functionality: Lists object names in the specified environment.
- Arguments: name (environment), pattern (regex filter), all.names (include hidden objects).
- Environments: Works with global, custom, and package environments.
- Use Cases: Debugging, package exploration, and environment management.