R Cookbook

1. Performing Vector Arithmetic
   
2. 
   
3. Problem
   
4. You want to operate on an entire vector at once.
   
5. 
   
6. Solution
   
7. The usual arithmetic operators can perform element-wise operations on entire vectors. Many functions operate on entire vectors, too, and return a vector result.
   
8. 
   
9. Discussion
   
10. Vector operations are one of R’s great strengths. All the basic arithmetic operators can be applied to pairs of vectors. They operate in an element-wise manner; that is, the operator is applied to corresponding elements from both vectors:
    
11. 
    
12. > v <- c(11,12,13,14,15)
    
13. > w <- c(1,2,3,4,5)
    
14. > v + w
    
15. [1] 12 14 16 18 20
    
16. > v - w
    
17. [1] 10 10 10 10 10
    
18. > v * w
    
19. [1] 11 24 39 56 75
    
20. > v / w
    
21. [1] 11.000000  6.000000  4.333333  3.500000  3.000000
    
22. > w ^ v
    
23. [1]           1        4096     1594323   268435456 30517578125

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1. Getting and Setting the Working Directory
   
2. 
   
3. Problem
   
4. You want to change your working directory. Or you just want to know what it is.
   
5. 
   
6. Solution
   
7. Command line
   
8. Use getwd to report the working directory, and use setwd to change it:
   
9. 
   
10. > getwd()
    
11. [1] "/home/paul/research"
    
12. > setwd("Bayes")
    
13. > getwd()
    
14. [1] "/home/paul/research/Bayes"

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1. Saving Your Workspace
   
2. 
   
3. Problem
   
4. You want to save your workspace without exiting from R.
   
5. 
   
6. Solution
   
7. Call the save.image function:
   
8. 
   
9. > save.image()

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1. Saving Your Workspace
   
2. 
   
3. Problem
   
4. You want to save your workspace without exiting from R.
   
5. 
   
6. Solution
   
7. Call the save.image function:
   
8. 
   
9. > save.image()

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1. Viewing Your Command History
   
2. 
   
3. Problem
   
4. You want to see your recent sequence of commands.
   
5. 
   
6. Solution
   
7. Scroll backward by pressing the up arrow or Ctrl-P. Or use the history function to view your most recent input:
   
8. 
   
9. > history()

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1. Saving the Result of the Previous Command
   
2. 
   
3. Problem
   
4. You typed an expression into R that calculated the value, but you forgot to save the result in a variable.
   
5. 
   
6. Solution
   
7. A special variable called .Last.value saves the value of the most recently evaluated expression. Save it to a variable before you type anything else.
   
8. 
   
9. Discussion
   
10. It is frustrating to type a long expression or call a long-running function but then forget to save the result. Fortunately, you needn’t retype the expression nor invoke the function again—the result was saved in the .Last.value variable:
    
11. 
    
12. > aVeryLongRunningFunction()     # Oops! Forgot to save the result!
    
13. [1] 147.6549
    
14. > x <- .Last.value               # Capture the result now
    
15. > x
    
16. [1] 147.6549

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just a look

1. Displaying the Search Path
   
2. 
   
3. Problem
   
4. You want to see the list of packages currently loaded into R.
   
5. 
   
6. Solution
   
7. Use the search function with no arguments:
   
8. 
   
9. > search()

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1. ccessing the Functions in a Package
   
2. 
   
3. Problem
   
4. A package installed on your computer is either a standard package or a package downloaded by you. When you try using functions in the package, however, R cannot find them.
   
5. 
   
6. Solution
   
7. Use either the library function or the require function to load the package into R:
   
8. 
   
9. > library(packagename)

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1. Accessing Built-in Datasets
   
2. 
   
3. Problem
   
4. You want to use one of R’s built-in datasets.
   
5. 
   
6. Solution
   
7. The standard datasets distributed with R are already available to you, since the datasets package is in your search path.
   
8. 
   
9. To access datasets in other packages, use the data function while giving the dataset name and package name:
   
10. 
    
11. > data(dsname, package="pkgname")

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