if-statements.qmd

---
title: "Using `if` statements"
---

Conditional statements are fundamental in programming, allowing for decision-making based on different conditions. In R, the primary conditional statement is the `if` statement, which can be used alone or combined with `else` and `else if` for more complex logic.

## Basic If Statement

The basic `if` statement checks a condition and executes a block of code if the condition is true.

**Syntax:**
```r
if (condition) {
  # code to execute if the condition is true
}
```

**Example:**
```r
x <- 10

if (x > 5) {
  print("x is greater than 5")
}
```

## If-Else Statement

To execute a block of code when the condition is false, use an `else` statement.

**Syntax:**
```r
if (condition) {
  # code to execute if the condition is true
} else {
  # code to execute if the condition is false
}
```

**Example:**
```r
x <- 3

if (x > 5) {
  print("x is greater than 5")
} else {
  print("x is not greater than 5")
}
```

### If-Else If-Else Statement

For multiple conditions, use `else if` to check additional conditions.

**Syntax:**
```r
if (condition1) {
  # code to execute if condition1 is true
} else if (condition2) {
  # code to execute if condition2 is true
} else {
  # code to execute if none of the conditions are true
}
```

**Example:**
```r
x <- 7

if (x > 10) {
  print("x is greater than 10")
} else if (x > 5) {
  print("x is greater than 5 but less than or equal to 10")
} else {
  print("x is 5 or less")
}
```

## Nested If Statements

You can also nest if statements inside one another to check multiple levels of conditions.

**Example:**
```r
x <- 15
y <- 20

if (x > 10) {
  if (y > 15) {
    print("x is greater than 10 and y is greater than 15")
  } else {
    print("x is greater than 10 but y is not greater than 15")
  }
} else {
  print("x is 10 or less")
}
```

### Vectorized If Statements

When working with vectors, `ifelse` is a more efficient way to apply conditional logic.

**Syntax:**
```r
ifelse(test, yes, no)
```
- `test`: A logical condition.
- `yes`: The value to return if the condition is true.
- `no`: The value to return if the condition is false.

**Example:**
```r
x <- c(2, 7, 5, 10)

result <- ifelse(x > 5, "Greater than 5", "5 or less")
print(result)
```

## Conclusion

Using if statements in R allows you to execute code based on conditions, making your programs more dynamic and flexible. Whether you're using a simple `if` statement, adding `else` and `else if` for more complex logic, or applying conditional logic to vectors with `ifelse`, mastering these constructs is essential for effective programming in R.