1 Getting Started

Author

Affiliation

Md Rasel Biswas

ISRT, University of Dhaka

1 Getting Started with R

When you type something into the console, R will give you a reply. For example:
```
2+4
#> [1] 6
```
As expected, R returned 6.

Note:

You can ignore the [1] you see in the output. It simply means that 6 is the “first element of the line.”

R can also be used as a calculator.

(59 + 73 + 2) / 3
#> [1] 44.66667
10^(3+1)
#> [1] 10000

Note:

Arithmetic operators in R are the same as in most other computer applications.

2 Arithmetic Operators

Description	Operator
Addition	`+`
Subtraction	`-`
Multiplication	`*`
Division	`/`
Exponentiation	`^` or `**`
Integer division	`x %/% y` (e.g., `10%/%3` is 3)
Modulus (remainder)	`x %% y` (e.g., `10%%3` is 1)

3 Exercise 1.1

Use R to calculate the following:
- \(5^2\)
- Add 8 to 22 and then multiply the result by 3
- Divide 8 by 2.5 and then divide the result by 3

Notice

These calculations do not create objects that are remembered by R.

4 Creating Objects

To store calculations in R, we assign them to objects.
Assignment operators <- or = can be used, but <- is preferred because = has other uses.
```
my_obj <- 48
```
Now that we’ve created this object, R will remember it during the current session.
All created objects are stored in the current workspace. In RStudio, you can see them under the Environment tab (top right pane).

If you switch from ‘List’ to ‘Grid’ view in the Environment tab, RStudio will show:
- the type (e.g., numeric)
- the length (number of values)
- the size in memory
- and the stored value

Objects can hold different types of values. For example:
```
my_obj2 <- "R is cool"
```
Here we created my_obj2, which stores a character string "R is cool".

Note

Strings must be in quotes.

If you forget, R will return an error.

my_obj2 <- R is cool
#> Error in parse(text = input): <text>:1:14: unexpected symbol
#> 1: my_obj2 <- R is
#>                  ^

Our workspace now contains both my_obj and my_obj2.

To change the value of an existing object, reassign it:
```
my_obj2 <- 1024
```
Now my_obj2 holds a numeric value instead of a string.

You can perform operations using objects. For example:
```
my_obj3 <- my_obj + my_obj2
my_obj3
#> [1] 1072
```
This creates my_obj3 with value \(48 + 1024 = 1072\).

If you try adding two character strings:

char_obj <- "hello"
char_obj2 <- "world!"
char_obj3 <- char_obj + char_obj2
#> Error in char_obj + char_obj2: non-numeric argument to binary operator

R will return an error because strings cannot be added.

Another common error is object * not found.

my_obj <- 48
my_obj4 <- my_obj + no_obj
#> Error: object 'no_obj' not found

Here, no_obj has not been created, so the operation fails.

5 Naming Objects

In R, object names are case sensitive.
Valid object names can include:
- letters (a-z, A-Z)
- digits (0-9)
- dot . and underscore _
Rules:
- Names cannot start with a number, hyphen -, or underscore _.
- Names can start with a dot, but only if followed by a letter.
- Non-syntactic names must be enclosed in backticks.
Good practice: use meaningful names for readability.
Avoid using names of existing R functions or keywords (mean, log, exp, TRUE, c, etc.).

6 Exercise 1.2

Create an object x1 with value 73.
Create x2 as the result of \(101+36\).
Multiply x1 and x2 and store it in x3.
Subtract 1 from x3 and calculate its 4th root.
The answer should be 10.

7 Use of Brackets

Parentheses ( ) are used to group expressions. They must be matched.
```
((3 + 12)/3 + 8)
#> [1] 13
```
Curly braces { } do not cause errors in expressions but have special uses (e.g., functions).
```
{10 + 2} + 5
#> [1] 17
```

Square brackets [ ] are used for indexing, not arithmetic:

[2 + 7]/3
#> Error in parse(text = input): <text>:1:1: unexpected '['
#> 1: [
#>     ^

8 R Functions

Functions are pre-written pieces of code.
Some examples:

Description	Function	Example
Square root	`sqrt`	`sqrt(225)`
Natural log	`log`	`log(50)`
Exponential	`exp`	`exp(3)`
Absolute value	`abs`	`abs(-10)`
Factorial	`factorial`	`factorial(6)`
Sine function	`sin`	`sin(25)`
Inverse cosine	`acos`	`acos(-1)`

General function structure:

function_name(arg1 = val1, arg2 = val2, ...)

Example:
```
sqrt(25)
#> [1] 5
sqrt(x = 25)
#> [1] 5
```

Both return 5.

Note

Inputs (called arguments) go inside parentheses ( ).
Multiple arguments are separated by commas.

9 Some Useful Built-in Functions

round(3.567, digits=2)
#> [1] 3.57
floor(3.567)
#> [1] 3
ceiling(3.567)
#> [1] 4
pi   # Not a function, but useful
#> [1] 3.141593

10 R Ignores Extra Spaces

(1+2)     ^     3
#> [1] 27
    ( 1+  2)    ^ 3
#> [1] 27

You can add spaces freely between elements.

But spaces inside a value cause errors:

3   .14
#> Error in parse(text = input): <text>:1:5: unexpected numeric constant
#> 1: 3   .14
#>         ^

11 Commenting Code

Use # to write comments. R ignores everything after #.

# Calculating BMI
weight <- 70   # in kg
height <- 1.7  # in meters
bmi <- weight / height ^ 2
bmi
#> [1] 24.22145

12 Running R Scripts

Instead of typing code line by line, you can save it in a script (.R file).

12.1 From R Console:

source("my_script.R")

Note

Make sure the script file is saved in your current working directory.
If it’s in another folder, provide the full file path.
Example: source("C:/Users/Rasel/Documents/my_script.R")

12.2 From Terminal:

Rscript my_script.R

Tip

source() runs inside your current R session (objects remain).
Rscript runs in a fresh session (objects do not remain).

13 Exercise 1.3

Why does this code not work?

my_variable <- 10
my_varıable
#> Error: object 'my_varıable' not found

14 Exercise 1.4

Create an object myObject with a value between 1 and 100.
Add 13 to myObject and update the object.
Check if myObject is divisible by 2, 3, 13, or 21.
How many times can 5 fit into myObject?

15 Exercise 1.5

Save this code into practice.R:
```
x <- 5
y <- 10
print(x + y)
```
Run it with source("practice.R") (R Console).
Run it with Rscript practice.R (Terminal).