Generating random numbers

Problem

You want to generate random numbers.

Solution

For uniformly distributed (flat) random numbers, use runif(). By default, its range is from 0 to 1.

  1. runif(1)
  2. #> [1] 0.09006613
  4. # Get a vector of 4 numbers
  5. runif(4)
  6. #> [1] 0.6972299 0.9505426 0.8297167 0.9779939
  8. # Get a vector of 3 numbers from 0 to 100
  9. runif(3, min=0, max=100)
  10. #> [1] 83.702278  3.062253  5.388360
  12. # Get 3 integers from 0 to 100
  13. # Use max=101 because it will never actually equal 101
  14. floor(runif(3, min=0, max=101))
  15. #> [1] 11 67  1
  17. # This will do the same thing
  18. sample(1:100, 3, replace=TRUE)
  19. #> [1]  8 63 64
  21. # To generate integers WITHOUT replacement:
  22. sample(1:100, 3, replace=FALSE)
  23. #> [1] 76 25 52

To generate numbers from a normal distribution, use rnorm(). By default the mean is 0 and the standard deviation is 1.

  1. rnorm(4)
  2. #> [1] -2.3308287 -0.9073857 -0.7638332 -0.2193786
  4. # Use a different mean and standard deviation
  5. rnorm(4, mean=50, sd=10)
  6. #> [1] 59.20927 40.12440 44.58840 41.97056
  8. # To check that the distribution looks right, make a histogram of the numbers
  9. x <- rnorm(400, mean=50, sd=10)
  10. hist(x)

plot of chunk unnamed-chunk-3

Notes

If you want to your sequences of random numbers to be repeatable, see ../Generating repeatable sequences of random numbers.