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#![allow(clippy::eq_op)]
use crate::common;
/// Find the maximum element in a collection.
/// If the collection is empty, returns `None`.
///
/// # Arguments
/// * `collection` - A slice of items.
///
/// # Returns
/// * `Option<T>` - The maximum item in the collection, or `None` if the collection is empty.
///
/// # Examples
/// ```rust
/// use lowdash::max;
/// let numbers = vec![5, 3, 8, 1, 4];
/// let result = max(&numbers);
/// assert_eq!(result, Some(8));
/// ```
///
/// ```rust
/// use lowdash::max;
/// let strings = vec!["apple", "banana", "cherry"];
/// let result = max(&strings);
/// assert_eq!(result, Some("cherry"));
/// ```
///
/// ```rust
/// use lowdash::max;
///
/// #[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
/// struct Person {
/// name: String,
/// age: u32,
/// }
///
/// let people = vec![
/// Person { name: "Alice".to_string(), age: 25 },
/// Person { name: "Bob".to_string(), age: 30 },
/// Person { name: "Cia".to_string(), age: 20 },
/// ];
///
/// let result = max(&people);
/// assert_eq!(
/// result,
/// Some(Person { name: "Cia".to_string(), age: 20 })
/// );
/// ```
///
/// ```rust
/// use lowdash::max;
/// let collection = vec![3.14, 2.71, -1.0, 0.0];
/// let result = max(&collection);
/// assert_eq!(result, Some(3.14));
/// ```
pub fn max<T>(collection: &[T]) -> Option<T>
where
T: PartialOrd + Clone + 'static,
{
if collection.is_empty() {
None
} else if common::is_collection_float(
&collection
.iter()
.map(|item| Box::new(item.clone()) as Box<dyn std::any::Any>)
.collect::<Vec<_>>(),
) {
let mut max = collection[0].clone();
for item in &collection[1..] {
if item > &max || max != max {
// note: NaN != NaN is true because NaN is not equal to itself
max = item.clone();
}
}
Some(max)
} else {
let mut max = collection[0].clone();
for item in &collection[1..] {
if item > &max {
max = item.clone();
}
}
Some(max)
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_max_numbers() {
let collection = vec![5, 3, 8, 1, 4];
let result = max(&collection);
assert_eq!(result, Some(8));
}
#[test]
fn test_max_strings() {
let collection = vec!["apple", "banana", "cherry"];
let result = max(&collection);
assert_eq!(result, Some("cherry"));
}
#[test]
fn test_max_empty_collection() {
let collection: Vec<i32> = vec![];
let result = max(&collection);
assert_eq!(result, None); // No maximum in an empty collection
}
#[test]
fn test_max_single_element() {
let collection = vec![42];
let result = max(&collection);
assert_eq!(result, Some(42));
}
#[test]
fn test_max_with_struct() {
#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Clone)]
struct Person {
age: u32,
name: String,
}
let people = vec![
Person {
age: 25,
name: "Alice".to_string(),
},
Person {
age: 30,
name: "Bob".to_string(),
},
Person {
age: 20,
name: "Cia".to_string(),
},
];
let result = max(&people);
assert_eq!(
result,
Some(Person {
age: 30,
name: "Bob".to_string()
})
);
}
#[test]
fn test_max_with_floating_points() {
let collection = vec![3.14, 2.71, -1.0, 0.0];
let result = max(&collection);
assert_eq!(result, Some(3.14));
}
#[test]
fn test_max_with_f32() {
let collection = vec![3.14f32, 2.71, -1.0, 0.0];
let result = max(&collection);
assert_eq!(result, Some(3.14f32));
}
#[test]
fn test_max_with_f64() {
let collection = vec![3.14f64, 2.71, -1.0, 0.0];
let result = max(&collection);
assert_eq!(result, Some(3.14f64));
}
#[test]
fn test_max_with_characters() {
let collection = vec!['z', 'a', 'm', 'b'];
let result = max(&collection);
assert_eq!(result, Some('z'));
}
#[test]
fn test_max_collection_with_nan() {
let collection = vec![std::f64::NAN, 2.0, 3.0];
let result = max(&collection);
// Since NaN comparisons are always false, the maximum should be 3.0
assert_eq!(result, Some(3.0));
}
#[test]
fn test_max_all_nan() {
let collection = vec![std::f64::NAN, std::f64::NAN];
let result = max(&collection);
assert!(result.unwrap().is_nan());
}
}