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Course Notes: Intermediate R

Intermediate R

Chapter 1: Conditionals and Control Flow

Relational Operators

Equality

  • TRUE == TRUE # returns TRUE
  • TRUE == FALSE # returns FALSE
  • "hello" == "goodbye" # FALSE
  • 3 == 2 # FALSE

Inequality !=

  • TRUE != TRUE # FALSE
  • TRUE != FALSE # returns TRUE
  • "hello" != "goodbye" # TRUE
  • 3 != 2 # TRUE

< and >

  • 3 < 5 # TRUE
  • 3 > 5 # FALSE
# Alphabetical Order!
"Hello" > "Goodbye" # TRUE

# TRUE coerces to 1
# FALSE coerces to 0
TRUE < FALSE # FALSE

<= and >=

  • 5 >= 3 # TRUE
  • 3 >= 3 # TRUE

Relational Operators & Vectors

linkedin <- c(16, 9, 13, 5, 2, 17, 14)
linkedin # 16, 9, 13, 5, 2, 17, 14

linkedin > 10 # TRUE, FALSE, TRUE, FALSE, FALSE, TRUE, TRUE

Logical Operators

  • AND &
  • OR |
  • NOT !

AND operator &

  • TRUE & TRUE # TRUE
  • FALSE & TRUE # FALSE
  • TRUE & FALSE # FALSE
  • FALSE & FALSE # FALSE
x <- 12
x > 5 & x < 15 # TRUE

x <- 17
x > 5 & x < 15 # FALSE

OR operator |

y <- 4
y < 5 | y > 15 # TRUE

y <- 14
y < 5 | y > 15 # FALSE

NOT operator !

  • !TRUE # FALSE
  • !FALSE # TRUE
  • !(X<5) # x >= 5
  • is.numeric(5) # TRUE
  • !is.numeric(5) # FALSE
  • is.numeric("hello") # FALSE
  • !is.numeric("hello") # TRUE

Logical Operators and Vectors

  • c(TRUE, TRUE, FALSE) & c(TRUE, FALSE, FALSE) # TRUE FALSE FALSE
  • c(TRUE, TRUE, FALSE) | c(TRUE, FALSE, FALSE) # TRUE TRUE FALSE
  • !c(TRUE, TRUE, FALSE) # FALSE FALSE TRUE

& vs &&, | vs. ||

  • c(TRUE, TRUE, FALSE) & c(TRUE, FALSE, FALSE) # TRUE FALSE FALSE
  • c(TRUE, TRUE, FALSE) && c(TRUE, FALSE, FALSE) # TRUE
  • c(TRUE, TRUE, FALSE) | c(TRUE, FALSE, FALSE) # TRUE TRUE FALSE
  • c(TRUE, TRUE, FALSE) || c(TRUE, FALSE, FALSE) # TRUE

Conditional Statements

if statement

if(condition) {  
	expr
}

x <- -3

if(x < 0) {
	print("x is a negative number")
} # "x is a negative number"

else statement

if(condition) {  
	expr1
} 	else 	{ 
	expr2
}

x <- 3

if(x < 0) {
	print("x is a negative number")
}	else {
	print("x is either a positive number or zero")
} # "x is a negative number"

x <- 5
if(x < 0) {  
	print("x is a negative number")
} 	else {  
	print("x is either a positive number or zero")
}	# "x is either a positive number or zero"

else if statement

if(condition1) {  
	expr1
} 	elseif(condition2) {  
	expr2
} 	else {  
	expr3
}

x <- 3

if(x < 0) {  
	print("x is a negative number")
} 	elseif(x == 0) {  
	print("x is zero")
} 	else {  
	print("x is a positive number")
}	# "x is a negative number"

x <- 0

if(x < 0) {  
	print("x is a negative number")
} 	elseif(x == 0) {  
	print("x is zero")
} 	else {  
	print("x is a positive number")
}	# "x is a zero"

x <- 5

if(x < 0) {  
	print("x is a negative number")
} 	elseif(x == 0) {  
	print("x is zero")
} 	else {  
	print("x is a positive number")
} 	# "x is a positive number"

if, else if, else

x <- 6

if(x %% 2 == 0) {  
	print("divisible by 2")
} 	elseif(x %% 3 == 0) {  
	print("divisible by 3")
} 	else {  
	print("not divisible by 2 nor by 3...")
}	# "divisible by 2"

Chapter 2: Loops

While loop

while(condition) {
	expr
}

while(ctr <= 7) {
	print(paste("ctr is set to", ctr))
	ctr <- ctr + 1
} # "ctr is set to 1"

while(ctr <= 7) {  
	print(paste("ctr is set to", ctr))  
	ctr <- ctr + 1
}	# "ctr is set to 2"

while(ctr <= 7) {  
	print(paste("ctr is set to", ctr)) 
	ctr <- ctr + 1
}	# "ctr is set to 7"

ctr <- 1
while(ctr <= 7) {  
	print(paste("ctr is set to", ctr))  
	ctr <- ctr + 1
} 
# "ctr is set to 1""ctr is set to 2"..."ctr is set to 7"

ctr
# 8

Infinite while loop

ctr <- 1
while(ctr <= 7) {  
	print(paste("ctr is set to", ctr))
} # "ctr is set to 1""ctr is set to 1""ctr is set to 1""ctr is set to 1""ctr is set to 1""ctr is set # to 1""ctr is set to 1"...

break statement

ctr <- 1
while(ctr <= 7) {
	if(ctr %% 5 == 0) {
		break
	}
	print(paste("ctr is set to", ctr))
	ctr <- ctr + 1
}
# "ctr is set to 1"
# "ctr is set to 2"
# "ctr is set to 3"
# "ctr is set to 4"

for loop

for(var in seq) {  
	expr
}
cities <- c("New York", "Paris", "London", "Tokyo",              
			"Rio de Janeiro", "Cape Town")
cities
# "New York"   "Paris"  ...  "Cape Town"

for(city in cities) {
	print(city)
} # "New York"

for loop over list

cities <- list("New York", "Paris", "London", 
				"Tokyo","Rio de Janeiro", "Cape Town")
for(city in cities) {  
	print(city)
}
# "New York"
# "Paris"
# "London"
# "Tokyo"
# "Rio de Janeiro"
# "Cape Town"

break statement

for(city in cities) {
	if(nchar(city) == 6) {
		break
	}
	print(city)
}
# "New York"
# "Paris"

next statement

for (city in cities) {
	if(nchar(city) == 6) {
		next
	}
	print(city)
}
# "New York"
# "Paris"
# "Tokyo"
# "Rio de Janeiro"
# "Cape Town"

for loop: v2

for(i in 1:length(cities)) {
	print(cities[i], "is on position"
			i, "in the cities vector.")
}
# "New York is on position 1 in the cities vector."
# "Paris is on position 2 in the cities vector."
# "London is on position 3 in the cities vector."
# "Tokyo is on position 4 in the cities vector."
# "Rio de Janeiro is on position 5 in the cities vector."
# "Cape Town is on position 6 in the cities vector."

for loop: wrap-up

# Concise, easy to read, but no access to looping index
for(city in cities) {  
	print(city)
}

#Harder to read and write, but more versatile
	for(i in 1:length(cities)) {  
	print(cities[i], "is on position",
			i, "in the cities vector."))
}

Chapter 3: Functions

  • You already know 'em!
  • Create a list: list()
  • Display a variable: print()
sd(c(1, 5, 6, 7))
values <- c(1, 5, 6, 7)
sd(values)
my_sd <- sd(values)
my_sd

Function Documentation

help(sd)
?sd

Argument Matching

sd(x, na.rm = FALSE)
By Position
sd(values)
By name
sd(x = values)

na.rm argument

values <- c(1, 5, 6, NA)
sd(values) # returns NA

sd(values, TRUE)
sd(values, na.rm = TRUE)

Useful trick

args(sd)
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