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use std::collections::HashMap;
use std::hash::Hash;
/// Counts the number of occurrences of each value in a collection.
///
/// This function iterates over a slice of items and returns a `HashMap` where each key is a unique
/// item from the collection, and the corresponding value is the number of times that item appears.
///
/// **Time Complexity:** O(n), where n is the number of elements in the collection.
///
/// # Arguments
///
/// * `collection` - A slice of items to be counted.
///
/// # Type Parameters
///
/// * `T` - The type of elements in the input collection. Must implement `Hash`, `Eq`, and `Clone`.
///
/// # Returns
///
/// * `HashMap<T, usize>` - A map where keys are unique items from the collection and values are their counts.
///
/// # Examples
///
/// ```rust
/// use lowdash::count_values;
/// use std::collections::HashMap;
///
/// let numbers = vec![1, 2, 2, 3, 4, 3, 5];
/// let result = count_values(&numbers);
/// let mut expected = HashMap::new();
/// expected.insert(1, 1);
/// expected.insert(2, 2);
/// expected.insert(3, 2);
/// expected.insert(4, 1);
/// expected.insert(5, 1);
/// assert_eq!(result, expected);
/// ```
///
/// ```rust
/// use lowdash::count_values;
/// use std::collections::HashMap;
///
/// #[derive(Debug, PartialEq, Eq, Hash, 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: "Alice".to_string(), age: 25 },
/// Person { name: "Carol".to_string(), age: 35 },
/// ];
///
/// let result = count_values(&people);
/// let mut expected = HashMap::new();
/// expected.insert(
/// Person { name: "Alice".to_string(), age: 25 },
/// 2
/// );
/// expected.insert(
/// Person { name: "Bob".to_string(), age: 30 },
/// 1
/// );
/// expected.insert(
/// Person { name: "Carol".to_string(), age: 35 },
/// 1
/// );
/// assert_eq!(result, expected);
/// ```
pub fn count_values<T>(collection: &[T]) -> HashMap<T, usize>
where
T: Hash + Eq + Clone,
{
let mut result = HashMap::new();
for item in collection {
*result.entry(item.clone()).or_insert(0) += 1;
}
result
}
#[cfg(test)]
mod tests {
use crate::common;
use super::*;
use std::collections::HashMap;
#[derive(Debug, PartialEq, Eq, Hash, Clone)]
struct Person {
name: String,
age: u32,
}
#[test]
fn test_count_values_integers() {
let numbers = vec![1, 2, 2, 3, 4, 3, 5];
let result = count_values(&numbers);
let mut expected = HashMap::new();
expected.insert(1, 1);
expected.insert(2, 2);
expected.insert(3, 2);
expected.insert(4, 1);
expected.insert(5, 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_strings() {
let strings = vec!["apple", "banana", "apple", "cherry", "banana"];
let result = count_values(&strings);
let mut expected = HashMap::new();
expected.insert("apple", 2);
expected.insert("banana", 2);
expected.insert("cherry", 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_with_structs() {
let people = vec![
Person {
name: "Alice".to_string(),
age: 25,
},
Person {
name: "Bob".to_string(),
age: 30,
},
Person {
name: "Alice".to_string(),
age: 25,
},
Person {
name: "Carol".to_string(),
age: 35,
},
];
let result = count_values(&people);
let mut expected = HashMap::new();
expected.insert(
Person {
name: "Alice".to_string(),
age: 25,
},
2,
);
expected.insert(
Person {
name: "Bob".to_string(),
age: 30,
},
1,
);
expected.insert(
Person {
name: "Carol".to_string(),
age: 35,
},
1,
);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_empty_collection() {
let empty: Vec<i32> = vec![];
let result = count_values(&empty);
let expected: HashMap<i32, usize> = HashMap::new();
assert_eq!(result, expected);
}
#[test]
fn test_count_values_no_duplicates() {
let collection = vec![1, 2, 3, 4, 5];
let result = count_values(&collection);
let mut expected = HashMap::new();
expected.insert(1, 1);
expected.insert(2, 1);
expected.insert(3, 1);
expected.insert(4, 1);
expected.insert(5, 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_all_duplicates() {
let collection = vec![2, 2, 2, 2];
let result = count_values(&collection);
let mut expected = HashMap::new();
expected.insert(2, 4);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_with_optionals() {
let collection = vec![Some(1), None, Some(2), Some(1), None, Some(3), Some(2)];
let result = count_values(&collection);
let mut expected = HashMap::new();
expected.insert(Some(1), 2);
expected.insert(None, 2);
expected.insert(Some(2), 2);
expected.insert(Some(3), 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_with_floats() {
let float_collection = vec![
common::Float(1.1),
common::Float(2.2),
common::Float(2.2),
common::Float(3.3),
common::Float(4.4),
common::Float(3.3),
common::Float(5.5),
];
let result = count_values(&float_collection);
let mut expected = HashMap::new();
expected.insert(common::Float(1.1), 1);
expected.insert(common::Float(2.2), 2);
expected.insert(common::Float(3.3), 2);
expected.insert(common::Float(4.4), 1);
expected.insert(common::Float(5.5), 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_with_characters() {
let chars = vec!['a', 'b', 'a', 'c', 'b', 'd'];
let result = count_values(&chars);
let mut expected = HashMap::new();
expected.insert('a', 2);
expected.insert('b', 2);
expected.insert('c', 1);
expected.insert('d', 1);
assert_eq!(result, expected);
}
#[test]
fn test_count_values_with_nan_floats() {
let float_collection = vec![
common::Float(std::f64::NAN),
common::Float(std::f64::INFINITY),
common::Float(std::f64::NAN),
common::Float(1.0),
];
let result = count_values(&float_collection);
let mut expected = HashMap::new();
expected.insert(common::Float(std::f64::NAN), 2);
expected.insert(common::Float(std::f64::INFINITY), 1);
expected.insert(common::Float(1.0), 1);
// Note: HashMap treats different NaN representations as distinct keys
assert_eq!(result.get(&common::Float(std::f64::NAN)), Some(&2));
assert_eq!(result.get(&common::Float(std::f64::INFINITY)), Some(&1));
assert_eq!(result.get(&common::Float(1.0)), Some(&1));
}
}