vectors3_answer.R

# Vectors 3 Answers

# run this, then do tasks below
x1 <- c(-1.2,  0.27,  1.08, -2.34,  0.42)
x2 <- c(18, 20, 21, 20, 24, 26, 27, 25, 24, 26, 26, 24, 23, 22, 40, 30)

# Refresher/mini-lession:

# You can use %in% to test if a value is present in a vector:
3 %in% c(1, 2, 3)
3 %in% c(4, 5, 6)
3 %in% c(3, 3, NA, 4)

# Use %in% to determine whether the value 20 is in x2
30 %in% x2


# To get the index position that value first occurs in a vector, use match()
match(3, c(1, 2, 3))
match(3, c(4, 5, 6))
match(3, c(3, 3, NA, 4))

# Find the first index of the value 24 in x2
match(24, x2)


# to get all index positions of a value in a vector, use which() with a boolean vector
which(3 == c(1, 2, 3))
which(3 == c(4, 5, 6))  
which(3 == c(3, 3, NA, 4))

# At what index positions does the value 20 appear in x2?
which(20 == x2)


# Change all values of 20 in x2 to 100; 
# hint: use the expression above to select the elements you want (put the expression inside the []), 
# then set the value to 100
x2[which(20 == x2)] <- 100
x2  # just to check


# set the third value in x1 to 5
x1[3] <- 5


# set the first and second values in x1 to 1 and 2 respectively
x1[1:2] <- c(1, 2)


# replace all values of 24 in x2 with 0
x2[x2 == 24] <- 0