13  R tutorial*

Variables

a = 5
b <- 5
c <- "Hello"

Assignment

a <- a + 1 # assignment
a == a + 1 # math equal

Vectors

u <- c(1,2,3,4,5)
v <- 6:10
b <- c('good', 'night', '😊')

Matrices

A <- matrix(c(1,2,3,4), nrow = 2, ncol = 2)
B <- matrix(c(5,6,7,8), nrow = 2, ncol = 2)

Linear algebra

u * v   # element-wise 
u %*% v # dot product
A * B   # element-wise
A %*% B # matrix multiplication
t(A)    # transpose
det(A)  # determinant 

Random numbers

# a random number from 0 to 100
runif(1, 0, 100)

# generate 10 random numbers
runif(10, 0, 100)

# random sampling
sample(1:100, 10)

Conditional statement

# draw a random integer
x <- sample(1:100, 1)

# if the remainder divided by 2 is 0
if (x %% 2 == 0) {
  
  # display it is an even number
  print("even number")

  } else {
  
    # otherwise, it is an odd number
    cat("odd number")

}

Loop

# for-loop
# loop for a given number of times
for (k in 1:10) {
  
  # the code to be repeated
  print("Hello!")
  
}

# while-loop
# loop on condition
k <- 0
while (k < 10) {
  
  # the code to be repeated
  print("Hello!")
  
  # keep track of the 
  k <- k + 1
}

# 1+2+...+100=?
s = 0;
k = 1;
while (k <= 100) {
  s <- s + k;
  k <- k + 1;
}

Functions

# built-in functions
sin(pi/2)
log(100)
exp(2.3)

# custom functions
square <- function(a) {
  a * a
}

# call the function
square(10)

# function as a reusable code block
seqsum <- function(begin, end) {
  s = 0;
  k = begin;
  while (k <= end) {
    s <- s + k;
    k <- k + 1;
  }
  return(s)
}

# function call
seqsum(1, 100)