#Example 1
f1 <- function(x, y) {
  x+y
}

f1( 3, 4)

#Example 2
f.bad <- function(x, y) {
 z1 <- 2*x + y
 z2 <- x + 2*y
 z3 <- 2*x + 2*y
 z4 <- x/y
}

f.bad(1, 2)

f.good <- function(x, y) {
 z1 <- 2*x + y
 z2 <- x + 2*y
 z3 <- 2*x + 2*y
 z4 <- x/y
 return( z1, z2, z3, z4)
}

f.good(1, 2)

#Example 3
f2 <- function(x, y) {
  z1 <- x + y
  z2 <- x + 2*y
  list(z1, z2) 
}

f2(2, 5)
f2(2, 5)[[1]]
f2(2, 5)[[2]]
f2(2, 5)$z1

#Example 4
f3 <- function(x, y) {
  z1 <- x + y
  z2 <- x + 2*y
  list(result1=z1, result2=z2)
}

f3(2, 5)
f3(2, 5)$result1
f3(2, 5)$result2


#Example 5
y <- f3( 1, 4)
names(y)
y$result2
y[[2]]

#Example 6
v1 <- seq(1, 6, 1)
v1
v2 <- seq(2, 12, 2)
v2
f3(v1, v2)

mat1 <- matrix( c(1, 2, 3, 4, 5, 6), ncol=2)
mat1
mat2 <- matrix( c(2, 4, 6, 8, 10, 12), ncol=2)
mat2
f3(mat1, mat2)

#Example 7
f4 <- function(x=3, y=2) {
  z1 <- x + y
  z2 <- x + 2*y
  list(result1=z1, result2=z2)
}

f4()

#using the default value for the y argument
f4(1, )$result1
f4(x=1)$result1

#using the default value for the x argument
f4( , 1)$result1
f4(y=1)$result1

#switching the order of the arguments
f4(y=1, x=	2)$result2

#Example 8
for(i in 2:4) {
    print(i)
}
	
#Example 9:
for(i in c(1, 3, 6, 9)) {
    z <- i + 1
}
z

#using the print statement to see result at each iteration
for(i in 3:5) {
    z <- i + 1
    print(z)
}


#The list does not have to contain numbers
cars <- c("Toyota", "Ford", "Chevy")
for(j in cars) { print(j) }

#Example 10:
f5 <- function(x) {
  for(i in 1:x) {
      y <- i*2
      print(y)
  }
  return(y*2)
}	

f5(3)	

#Example 11
names1 <- c("Dave", "John", "Ann", "Roger", "Bill")
f.names <- function(x) {
	for(name in x){
		if(name=="Roger")
			break
		print(name)
	}
}
f.names(names1)

#Example 12
i <- 2 
while(i <= 4) {
	i <- i+1
   print(i)
}

#Example 13
f6 <- function(x) {
	i <- 0 
  while(i < x) {
	i <- i+1
   y <- i*2
   print(y)
  }
  return(y*2)
}	 
f6(3)

#Example 14
names1 <- c("Dave", "John", "Ann", "Roger", "Bill")
f.names.while <- function(x) {
	i <- 1
	while( x[i] != "Roger"){
		print(x[i])
		i <- i+1
	}
}

f.names.while(names1)

#Example 15
i <- 2 
repeat {
	print(i)
	i <- i+1
	if(i > 4)
		break
}

#Example 16
names1 <- c("Dave", "John", "Ann", "Roger", "Bill")
f.names.repeat <- function(x)  {
	i <- 1
	repeat {
		print(x[i])
		i <- i+1
		if(x[i] == "Roger")
			break
	}
}

f.names.repeat(names1)

#Example 17
random.sample1 <- function(epsilon) {
	i <- 0
	repeat {
		i = i+1
       mean.test <- abs( mean( rnorm(100) ) )
       if (mean.test < epsilon )
			break
		}
		list(mean=mean.test, number.iterations=i)
	}

random.sample1(0.0001)

#Example 18
x <- seq(1:5)
ifelse(x < 3, "T", "F")

#Example 19	
norm2 <- rnorm(10, mean=2)
norm2
log.normal <- ifelse(norm2<0, 0 , log(norm2) )
log.normal

#Example 20
f1 <- function(x, ...) {
	y <- x+2
	return(y)
	#other commands
}

f2 <- function( ... , x) {
	y <- x+2
	return(y)
	#other commands
}

f1(3)
f1(x=3)
#f2(3)
f2(x=3)

#Example 21:
x <- rnorm(100)
y <- x + rnorm(100)

windows(5,5)
plot(x, y)

windows(5,5)
my.plot <- function(..., pch.new=15) {
	plot(..., pch=pch.new)
}

my.plot(x, y)