## 9.2 Exercise 2. Numeric vector manipulation

### 9.2.1 Exercise 2a.

Create the script “exercise2.R” and save it to the “Rcourse/Module1” directory: you will save all the commands of exercise 2 in that script.

Remember you can comment the code using #.

**1- Go to Rcourse/Module1
First check where you currently are with getwd();
then go to Rcourse/Module1 with setwd()**

**2- Create a numeric vector “y” which contains the numbers from 2 to 11, both included.**

Show y in the console.

## correction

`## [1] 2 3 4 5 6 7 8 9 10 11`

**3- How many elements are in y? I.e what is the length of vector y ?**

**4- Show the 2nd element of y.**

**5- Show the 3rd and the 6th elements of y.**

**6- Remove the 4th element of y: reassign. What is now the length of y ?**

**7- Show all elements of y that are inferior to 7.**

## correction

`## [1] TRUE TRUE TRUE TRUE FALSE FALSE FALSE FALSE FALSE`

`## [1] 2 3 4 6`

**8- Show all elements of y that are superior or equal to 4 and inferior to 9.**

**9- Create the vector x of 1000 random numbers from the normal distribution:**
*First read the help page of the rnorm() function.*

## correction

**10. What are the mean, median, minimum and maximum values of x?**

## correction

`## [1] -0.04611927`

`## [1] -0.04431017`

`## [1] -3.032328`

`## [1] 4.079495`

**11- Run the summary() function on x. What additional information do you obtain ?**

## correction

```
## Min. 1st Qu. Median Mean 3rd Qu. Max.
## -3.03233 -0.74507 -0.04431 -0.04612 0.66838 4.07949
```

**12- Create vector y2 as:**

**13- Which elements of y2 are also present in y ?Note: remember the %in% operator.**

**14- Multiply each element of y2 by 1.5: reassign.**

## correction

**15- Use the function any() to check if the number 3 is present.Check the help page of any()!**

## correction

`## [1] TRUE`

### 9.2.2 Exercise 2b.

**1- Create the vector myvector as:**

**Create the same vector using the rep.int() function (?rep.int)**

## correction

**2- Reassign the 5th, 6th and 7th position of myvector with the values 8, 12 and 32, respectively.**

## correction

**3- Calculate the fraction/percentage of each element of myvector (relative to the sum of all elements of the vector).Note:sum() can be useful…**

## correction

```
# sum of all elements of the vector
mytotal <- sum(myvector)
# divide each element by the sum
myvector / mytotal
```

```
## [1] 0.015625 0.031250 0.046875 0.015625 0.125000 0.187500 0.500000 0.031250
## [9] 0.046875
```

`## [1] 1.5625 3.1250 4.6875 1.5625 12.5000 18.7500 50.0000 3.1250 4.6875`

**4- Add vector c(2, 4, 6, 7) to myvector (combining both vectors): reassign!**

## correction

```
# create the new vector
newvector <- c(2, 4, 6, 7)
# combine both myvector and newvector
c(myvector, newvector)
```

`## [1] 1 2 3 1 8 12 32 2 3 2 4 6 7`