Information about variables

Problem

You want to find information about variables.

Solution

Here are some sample variables to work with in the examples below:

  1. x <- 6
  2. n <- 1:4
  3. let <- LETTERS[1:4]
  4. df <- data.frame(n, let)

Information about existence

  1. # List currently defined variables
  2. ls()
  3. #> [1] "df"       "filename" "let"      "n"        "old_dir"  "x"
  6. # Check if a variable named "x" exists
  7. exists("x")
  8. #> [1] TRUE
  10. # Check if "y" exists
  11. exists("y")
  12. #> [1] FALSE
  15. # Delete variable x
  16. rm(x)
  17. x
  18. #> Error in eval(expr, envir, enclos): object 'x' not found

Information about size/structure

  1. # Get information about structure
  2. str(n)
  3. #>  int [1:4] 1 2 3 4
  5. str(df)
  6. #> 'data.frame':    4 obs. of  2 variables:
  7. #>  $ n  : int  1 2 3 4
  8. #>  $ let: Factor w/ 4 levels "A","B","C","D": 1 2 3 4
  11. # Get the length of a vector
  12. length(n)
  13. #> [1] 4
  15. # Length probably doesn't give us what we want here:
  16. length(df)
  17. #> [1] 2
  19. # Number of rows
  20. nrow(df)
  21. #> [1] 4
  23. # Number of columns
  24. ncol(df)
  25. #> [1] 2
  27. # Get rows and columns
  28. dim(df)
  29. #> [1] 4 2