--Managing Vectors

A vector is a sequence of data elements of the same basic type: numeric, character, logical, factors, or dates (exclude: two additional vector types - complex and raw)

#Creating Vectors

Four main ways to create a vector: :, c(), seq(), rep()

# integer vector
w <- 8:17
w
##  [1]  8  9 10 11 12 13 14 15 16 17

# double precision floating point (number with decimals) vector
x <- c(0.5, 0.6, 0.2)
x
## [1] 0.5 0.6 0.2

# logical vector
y <- c(TRUE, FALSE, FALSE)
y
## [1]  TRUE FALSE FALSE

# Character vector
z <- c("a", "b", "c") 
z
## [1] "a" "b" "c"

# generate a sequence of numbers from 1 to 21 by increments of 2
seq(from = 1, to = 21, by = 2)             
##  [1]  1  3  5  7  9 11 13 15 17 19 21

# generate a sequence of numbers from 1 to 21 that has 15 equal 
# incremented 
# numbers
seq(0, 21, length.out = 15)    
##  [1]  0.0  1.5  3.0  4.5  6.0  7.5  9.0 10.5 12.0 13.5 15.0 16.5 
# 18.0 19.5
## [15] 21.0


# replicates the values in x a specified number of times in a 
# collated fashion
rep(1:4, times = 2)   
## [1] 1 2 3 4 1 2 3 4

# replicates the values in x in an uncollated fashion
rep(1:4, each = 2)    
## [1] 1 1 2 2 3 3 4 4

#Coercing Vectors

When you attempt to combine different types of elements (i.e. character and numeric) they will be coerced to the most flexible type possible:

# numerics are turned to characters
str(c("a", "b", "c", 1, 2, 3))
##  chr [1:6] "a" "b" "c" "1" "2" "3"

# logical are turned to numerics...
str(c(1, 2, 3, TRUE, FALSE))
##  num [1:5] 1 2 3 1 0

# or character
str(c("A", "B", "C", TRUE, FALSE))
##  chr [1:5] "A" "B" "C" "TRUE" "FALSE"

class(state.region)
## [1] "factor"

state.region2 <- as.character(state.region)
class(state.region2)
## [1] "character"

#Adding on to Vectors

v1 <- 8:17

c(v1, 18:22)
##  [1]  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22

# same as
c(v1, c(18, c(19, c(20, c(21:22)))))
##  [1]  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22

#Adding Attributes to Vectors

attributes(v1)
## NULL

# assigning names to a pre-existing vector
names(v1) <- letters[1:length(v1)]
v1
##  a  b  c  d  e  f  g  h  i  j 
##  8  9 10 11 12 13 14 15 16 17
attributes(v1)
## $names
##  [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"

# adding names when creating vectors
v2 <- c(name1 = 1, name2 = 2, name3 = 3)
v2
## name1 name2 name3 
##     1     2     3
attributes(v2)
## $names
## [1] "name1" "name2" "name3"

comment(v1) <- "This is a comment on a vector"
v1
##  a  b  c  d  e  f  g  h  i  j 
##  8  9 10 11 12 13 14 15 16 17
attributes(v1)
## $names
##  [1] "a" "b" "c" "d" "e" "f" "g" "h" "i" "j"
## 
## $comment
## [1] "This is a comment on a vector"

#Subsetting Vectors

• Positive integers

• Negative integers

• Logical values

• Names

Subsetting with positive integers:

v1
##  a  b  c  d  e  f  g  h  i  j 
##  8  9 10 11 12 13 14 15 16 17

v1[2]
## b 
## 9

v1[2:4]
##  b  c  d 
##  9 10 11

v1[c(2, 4, 6, 8)]
##  b  d  f  h 
##  9 11 13 15

# note that you can duplicate index positions
v1[c(2, 2, 4)]
##  b  b  d 
##  9  9 11

Subsetting with negative integers:

v1[-1]
##  b  c  d  e  f  g  h  i  j 
##  9 10 11 12 13 14 15 16 17

v1[-c(2, 4, 6, 8)]
##  a  c  e  g  i  j 
##  8 10 12 14 16 17

Subsetting with logical values:

v1[c(TRUE, FALSE, TRUE, FALSE, TRUE, TRUE, TRUE, FALSE, FALSE, TRUE)]
##  a  c  e  f  g  j 
##  8 10 12 13 14 17

v1[v1 < 12]
##  a  b  c  d 
##  8  9 10 11

v1[v1 < 12 | v1 > 15]
##  a  b  c  d  i  j 
##  8  9 10 11 16 17

# if logical vector is shorter than the length of the vector being
# subsetted, it will be recycled to be the same length
v1[c(TRUE, FALSE)]
##  a  c  e  g  i 
##  8 10 12 14 16

Subsetting with names:

v1["b"]
## b 
## 9

v1[c("a", "c", "h")]
##  a  c  h 
##  8 10 15

Simplifying vs. Preserving:

Simplifying subsets returns the simplest possible data structure that can represent the output. Preserving subsets keeps the structure of the output the same as the input.

v1[1]
## a 
## 8

v1[[1]]
## [1] 8

#Exercises

1. Check out the built-in character vector state.name.

2. How many elements are in this vector?

3. What attributes does this vector have?

4. Can you name each vector element with “V1”, “V2”, …, “V50” (shortcut: paste0("v", 1:50))?

5. Now what attributes does this vector have?

6. Subset state.name for those elements with the following names: V35, V17, V14, V38.