R - Sampling Data

• sample function
• sample takes a sample of the specified size from the elements of x using either with or without replacement.

 > sample(1:6, 4, replace = TRUE)  
 [1] 5 3 3 2  # duplicated number could be generated with replace option

• sample without duplicated number

 > sample(1:20, 10)  
  [1] 16 15 2 20 12 1 13 5 18 11  

• predefined English alphabet variable in R - LETTERS

 > LETTERS  
  [1] "A" "B" "C" "D" "E" "F" "G" "H" "I" "J" "K" "L" "M" "N" "O" "P" "Q" "R" "S" "T" "U" "V" "W" "X" "Y" "Z"  

• sample 10 characters with "a" and "b" with probability of 50% respectively

 > sample(c("a","b"), 10, replace = TRUE, prob = c(0.5, 0.5))  
  [1] "b" "a" "a" "b" "a" "a" "a" "a" "a" "a"  

• if we would like to generate 10 numbers with binominal data (0 or 1), we could use rbinom()

 > rbinom(n = 10, size = 1, prob = 0.7)  
  [1] 1 0 1 1 0 0 0 1 1 1  

• replicate() creates matrix, (replicate the function for n times)

 > replicate(10,rbinom(n = 10, size = 1, prob = 0.7))  
    [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]  
  [1,]  0  1  1  1  0  0  1  1  1   1  
  [2,]  1  1  1  1  1  1  1  1  1   1  
  [3,]  0  1  1  1  1  0  1  1  1   1  
  [4,]  1  0  1  1  0  1  1  1  0   1  
  [5,]  0  0  1  1  1  1  0  1  0   0  
  [6,]  1  0  1  0  1  1  0  1  1   0  
  [7,]  1  0  0  1  1  0  1  1  1   0  
  [8,]  0  1  1  0  1  1  1  1  1   0  
  [9,]  0  0  1  1  1  1  1  1  1   1  
 [10,]  1  0  1  1  1  1  0  0  0   1  

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