r_vectors

Question 1

What are 2 ways to do the following?

Create a vector named “codes” with the following characteristics:

• Three regions with corresponding values
  
  • italy = 380
  • canada = 124
  • egypt = 818

Answer 1

Way 1: codes <- c(“italy”=380, “canada”=124, “egypt”=818)

Way 2:

• > codes <- ‘a’
• > codes <- c(380,124,818)
• > country <- c(“italy”,”canada”,”egypt”)
• > names(codes) <- country
• > codes

Question 2

Create a sequence from 1 to 10

Create a sequency from 1 to 10, in intervals of 2

Answer 2

seq(1,10)

seq(1,10,2)

Question 3

How do you get the second element of the vector “codes”

Answer 3

codes[2]

Question 4

How do you get the first and third elements of the vector “codes”

Answer 4

codes[c(1,3)]

Question 5

How do you access the first thru the third elements of the vector “codes”

Answer 5

codes[1:3]

Question 6

How do you access the element named “canada” within the vector “codes”

Answer 6

codes[“canada”]

Question 7

• How do you access the elements named “egypt” and “italy” within the vector “temp”?
  
  • Way 1: names
  • Way 2: index values 3 and 5

Answer 7

• Way 1: temp[“egypt”,”italy”]
• Way 2: temp[c(3,5)]

Question 8

What is “coercion” in R

Answer 8

• When R attempts to coerce a value into a data type it “thinks” it should be, when incomplete or contradicting information is provided.

Question 9

As an example of coercion:

• What happens if you type the following:
• x <- c(1, “canada”, 3)

Answer 9

• R will create a vector of three character strings (converting 1 and 3 to strings)
• Output of x: “1” “canada” “3”

Question 10

How would you convert the vector 1:5 into characters

Answer 10

• x < 1:5
• y < as.character(x)

Question 11

What would happen if you type the following code:

• x <- c(“1”, “b”, “3”)
• as.numeric(x)

Answer 11

• R tries coercion
• Output:
  
  • 1 NA 3
  • Warning message: NAs introduced by coercion

Question 12

Associate the “city” vector to the “temp” vector

Answer 12

names(temp) <- city

Question 13

Get the first three cities in the temp vector

Answer 13

temp[1:3]