October 1st, 2018

There are two ideas here:

- Separate important from secondary things
- Content is important
- Structure is important
- Style is not important

- Tell to the computer what is the role of each part
- Later you can decide the style
- You can even change it later

- Group of values, all with the same type
- Basic types are
- Character
- Numeric
- Logic
- Factor

Vectors are so useful that we have several ways to create them

For example, the function `c(3,1,4)`

will give us a vector

We can also make vectors with incrementing numbers or repeating numbers

A vector with numbers between 4 and 9

4:9

[1] 4 5 6 7 8 9

seq(4, 9)

[1] 4 5 6 7 8 9

The two commands are equivalent. The first is easier to write

We can go from 4 to 10 incrementing by 2

seq(4, 10, 2)

[1] 4 6 8 10

We can say *how many* numbers we want, instead of the last value

seq(from=4, by=2, length=4)

[1] 4 6 8 10

rep(1, 3)

[1] 1 1 1

rep(c(7, 9, 13), 3)

[1] 7 9 13 7 9 13 7 9 13

rep(c(7, 9, 13), 1:3)

[1] 7 9 9 13 13 13

rep(1:2, c(10, 5))

[1] 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2

rep(c(TRUE, FALSE), 3)

[1] TRUE FALSE TRUE FALSE TRUE FALSE

rep(c(TRUE, FALSE), c(3, 3))

[1] TRUE TRUE TRUE FALSE FALSE FALSE

- In practice there are cases when a datum is not present
- It is not a good idea to use a fictitious value
- The symbol NA is used in that case
- You can use it on any vector, regardless of type

c(NA, TRUE, FALSE)

[1] NA TRUE FALSE

c(NA, 1, 2)

[1] NA 1 2

To get the *i*-th element of a vector `v`

we use `v[i]`

weight <- c(60, 72, 57, 90, 95, 72) weight

[1] 60 72 57 90 95 72

weight[3]

[1] 57

The value inside `[]`

is called *index* (plural: *indices*)

weight[c(1,3,5)]

[1] 60 57 95

weight[2:4]

[1] 72 57 90

Used to indicate omitted elements

weight

[1] 60 72 57 90 95 72

weight[c(-1,-3,-5)]

[1] 72 90 72

Useful when you need almost all elements

Vectors can be indexed by a logical vector

Must be of the same length of the vector

weight>72

[1] FALSE FALSE FALSE TRUE TRUE FALSE

weight[weight>72]

[1] 90 95

**This is very useful**

Every element of a vector can have a name

names(weight) <- c("Ali", "Deniz", "Fatma", "Emre", "Volkan", "Onur") weight

Ali Deniz Fatma Emre Volkan Onur 60 72 57 90 95 72

We can assign names to the elements when we create the vector

height <- c(Ali=1.75, Deniz=1.80, Fatma=1.65, Emre=1.90, Volkan=1.74, Onur=1.91) height

Ali Deniz Fatma Emre Volkan Onur 1.75 1.80 1.65 1.90 1.74 1.91

If a vector has names, we can use them as indices:

weight[c("Deniz", "Volkan", "Fatma")]

Deniz Volkan Fatma 72 95 57

- How do we know if a vector has names?

names(vector)

NULL

- Indices allow us to see
**and modify**parts of a vector - Indices can be
- positive integer vectors
- negative integer vectors
- logic vectors
- character vectors

- Index vectors can be of length 1 or longer
- except logic indices, which have to be of the
**same size**as the original vector

- except logic indices, which have to be of the