# Conditional Statement
## `if` statement
An "`if` statement" is written with the `if` keyword, and it is used to specify a block of code to be executed if a condition is `TRUE`:
{% tabs %}
{% tab title="Syntax" %}
```r
if (condition){
# Statements
}
```
{% endtab %}
{% tab title="Example" %}
```
# Age of two people
adam <- 33
bob <- 45
# Run the if statement
if (bob > adam){
print("bob is older than adam")
}
```
{% endtab %}
{% endtabs %}
### `else if` Statement
The `else if` keyword is R's way of saying "if the previous conditions were not true, then try this condition".
NOTE: We can add as many `else if` condition as we need.
{% tabs %}
{% tab title="Syntax" %}
```r
if (condition){
# Statements
} else if (condition_2){
# Statements_2
} else if (condition_3){
# Statements_3
} ## Add as much "else if" as you need.
```
{% endtab %}
{% tab title="Example" %}
```r
# Age of two people
adam <- 33
bob <- 33
# Run the if statement
if (bob > adam){
print("bob is older than adam")
} else if (bob == adam){
print("They are both same age")
}
```
{% endtab %}
{% endtabs %}
### `else` Statement
The `else` keyword catches anything that isn't caught by the preceding conditions:
{% tabs %}
{% tab title="Syntax" %}
```r
if (condition){
# Statements
} else if (condition_2){
# Statements_2
} else {
# Last Statement
}
```
You can also use `else` without `else if`:
```r
if (condition){
# Statements
} else {
# Last Statement
}
```
{% endtab %}
{% tab title="Example" %}
```r
a <- 200
b <- 33
if (b > a) {
print("b is greater than a")
} else if (a == b) {
print("a and b are equal")
} else {
print("a is greater than b")
}
```
**Code Breakdown**:
In this example, **`a`** is greater than **`b`**, so the first condition is not true, also the `else if` condition is not true, so we go to the `else` condition and print to screen that "**a is greater than b**".
{% endtab %}
{% endtabs %}
### Nested `if` Statement
You can also have `if` statements inside `if` statements, this is called ***nested*** `if` statements.
{% tabs %}
{% tab title="Syntax" %}
```r
if (condition){
if (condition2){
# Statement
}
else {
# Statement2
}
}
else {
# Statement3
}
```
{% endtab %}
{% tab title="Example" %}
```r
x <- 40
if (x > 20) {
print("Larger than 20")
if (x %% 20 == 0) {
print("and also an even number")
} else {
print("but odd number")
}
} else {
print("below 20.")
}
```
{% endtab %}
{% endtabs %}
## `switch case` Statement
**Switch case** statements are a substitute for long if statements that compare a variable to several integral values. `switch case` in R is a multiway branch statement. It allows a variable to be tested for equality against a list of values.
The `switch` statement follows the approach of mapping and searching over a list of values. If there is more than one match for a specific value, then the switch statement will return the first match found of the value matched with the expression.
{% tabs %}
{% tab title="Syntax" %}
```r
# Simple syntax
switch(expression, case1, case2, case3....)
# Syntax in Details
switch (expression,
"case 1" = Execute when the expression result matches case 1,
"case 2" = Execute when the expression result matches case 2,
"case 3" = When the expression result matches case 3, Execute these,
....
....
"case N" = When the expression result matches case N, Execute these lines,
Default Statements
)
```
Here, the expression is matched with the list of values and the corresponding value is returned.
* The expression value should be either integer or characters (We can write the expression as n/2 also, but the result should be an integer or convertible integer).
* An R Switch statement allows us to add a default statement. The default statements will be executed if the Expression value or the Index\_Position does not match any of the cases.
* The first matching statement will be returned if there is more than one match.
{% endtab %}
{% tab title="Example\_1" %}
```r
weekDay <- 3
switch(weekDay,
'1' = print("Saturday"),
'2' = print("Sunday"),
'3' = print("Monday"),
'4' = print("Tuesday"),
'5' = print("Wednesday"),
'6' = print("Thursday"),
'7' = print("Friday"),
print("Not a valid input")
)
```
**Code Breakdown****:** Here,
* `weekDay` : is the expression that takes the input.
* Our code will show output based on the input, when input matches with a **case** inside the code, it will print related output.
* If the input doesn't match with any **case** inside the code, it will print the **default case**. In this code default **case** is `print("Not a valid input")`.
{% endtab %}
{% tab title="Example\_2" %}
```r
cal1 = 6
cal2 = 7
cal3 = "p"
switch(cal3,
"a"= cat("Addition =", cal1 + cal2),
"d"= cat("Subtraction =", cal1 - cal2),
"r"= cat("Division = ", cal1 / cal2),
"s"= cat("Multiplication =", cal1 * cal2),
"m"= cat("Modulus =", cal1 %% cal2),
"p"= cat("Power =", cal1 ^ cal2)
)
```
**Code Breakdown****:** Here,
The `cat()` function in R is used to concatenate objects and print them to the console or a file. The basic syntax of the function is `cat(..., file = "", sep = " ", append = FALSE)`, where `...` represents the objects to concatenate, `file` is the file name to send output to, `sep` is the separator to use between objects, and `append` is a logical value indicating whether to append output to an existing file or create a new file. The function can be used in different ways, such as concatenating strings with a specified separator, outputting results to a file, and printing character strings in a readable format. To save the output of the `cat()` function as a value in R, it is recommended to use the `paste()` function instead.
{% endtab %}
{% endtabs %}
## Sources
The sources of the contents on this page are:
1.
2.
3.
4.
5. [R for Data Science Full Course | Data Science Training | Edureka](https://youtu.be/ckdHNu4kfL0?t=2605)
