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use std::collections::HashMap;
use std::hash::Hash;
/// Divide a collection into partitions based on a key extracted by a provided function,
/// preserving the order of elements and the order of partitions as they first appear.
///
/// This function takes a slice of items and splits it into multiple partitions. Each partition
/// contains elements that share the same key, as determined by the `iteratee` function.
/// The order of partitions corresponds to the order in which their keys first appear in the collection.
///
/// **Time Complexity:**
/// O(n), where n is the number of elements in the collection.
///
/// # Arguments
///
/// * `collection` - A slice of items to be partitioned.
/// * `iteratee` - A function that takes a reference to an item and returns a key of type `K`.
///
/// # Type Parameters
///
/// * `T` - The type of elements in the collection. Must implement `Clone`.
/// * `K` - The type of the key extracted from each element used to determine partitions. Must implement `Hash`, `Eq`, and `Clone`.
/// * `F` - The type of the iteratee function. Must implement `Fn(&T) -> K`.
///
/// # Returns
///
/// * `Vec<Vec<T>>` - A vector of partitions, where each partition is a vector of elements sharing the same key.
///
/// # Examples
///
/// ```rust
/// use lowdash::partition_by;
///
/// let numbers = vec![1, 2, 2, 3, 4, 3, 5];
/// let partitions = partition_by(&numbers, |x| *x);
/// assert_eq!(
/// partitions,
/// vec![vec![1], vec![2, 2], vec![3, 3], vec![4], vec![5]]
/// );
/// ```
///
/// ```rust
/// use lowdash::partition_by;
///
/// #[derive(Debug, PartialEq, 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 partitions = partition_by(&people, |p| p.age);
/// assert_eq!(
/// partitions,
/// vec![
/// vec![
/// Person { name: "Alice".to_string(), age: 25 },
/// Person { name: "Alice".to_string(), age: 25 },
/// ],
/// vec![
/// Person { name: "Bob".to_string(), age: 30 },
/// ],
/// vec![
/// Person { name: "Carol".to_string(), age: 35 },
/// ],
/// ]
/// );
/// ```
pub fn partition_by<T, K, F>(collection: &[T], iteratee: F) -> Vec<Vec<T>>
where
T: Clone,
K: Eq + Hash + Clone,
F: Fn(&T) -> K,
{
let mut seen: HashMap<K, usize> = HashMap::new();
let mut result: Vec<Vec<T>> = Vec::new();
for item in collection {
let key = iteratee(item);
if let Some(&index) = seen.get(&key) {
result[index].push(item.clone());
} else {
seen.insert(key.clone(), result.len());
result.push(vec![item.clone()]);
}
}
result
}
#[cfg(test)]
mod tests {
use super::*;
#[derive(Debug, PartialEq, Clone)]
struct Person {
name: String,
age: u32,
}
#[derive(Debug, PartialEq, Clone)]
struct Item {
id: u32,
value: String,
}
#[test]
fn test_partition_by_integers() {
let numbers = vec![1, 2, 2, 3, 4, 3, 5];
let partitions = partition_by(&numbers, |x| *x);
assert_eq!(
partitions,
vec![vec![1], vec![2, 2], vec![3, 3], vec![4], vec![5]]
);
}
#[test]
fn test_partition_by_strings() {
let strings = vec!["apple", "banana", "apple", "cherry", "banana"];
let partitions = partition_by(&strings, |s| s.to_string());
assert_eq!(
partitions,
vec![
vec!["apple", "apple"],
vec!["banana", "banana"],
vec!["cherry"]
]
);
}
#[test]
fn test_partition_by_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 partitions = partition_by(&people, |p| p.age);
assert_eq!(
partitions,
vec![
vec![
Person {
name: "Alice".to_string(),
age: 25
},
Person {
name: "Alice".to_string(),
age: 25
},
],
vec![Person {
name: "Bob".to_string(),
age: 30
},],
vec![Person {
name: "Carol".to_string(),
age: 35
},],
]
);
}
#[test]
fn test_partition_by_with_empty_collection() {
let empty: Vec<i32> = vec![];
let partitions = partition_by(&empty, |x| *x);
assert_eq!(partitions, Vec::<Vec<i32>>::new());
}
#[test]
fn test_partition_by_with_no_duplicates() {
let collection = vec![1, 2, 3, 4, 5];
let partitions = partition_by(&collection, |x| *x);
assert_eq!(
partitions,
vec![vec![1], vec![2], vec![3], vec![4], vec![5]]
);
}
#[test]
fn test_partition_by_with_all_duplicates() {
let collection = vec![1, 1, 1, 1, 1];
let partitions = partition_by(&collection, |x| *x);
assert_eq!(partitions, vec![vec![1, 1, 1, 1, 1]]);
}
#[test]
fn test_partition_by_with_floats() {
let float_collection: Vec<f64> = vec![1.1, 2.2, 2.2, 3.3, 4.4, 3.3, 5.5];
let partitions = partition_by(&float_collection, |x| x.to_bits());
assert_eq!(
partitions,
vec![
vec![1.1],
vec![2.2, 2.2],
vec![3.3, 3.3],
vec![4.4],
vec![5.5]
]
);
}
#[test]
fn test_partition_by_with_characters() {
let chars = vec!['a', 'b', 'a', 'c', 'b', 'd'];
let partitions = partition_by(&chars, |c| *c);
assert_eq!(
partitions,
vec![vec!['a', 'a'], vec!['b', 'b'], vec!['c'], vec!['d']]
);
}
#[test]
fn test_partition_by_preserves_order() {
let numbers = vec![3, 1, 2, 3, 2, 4, 1, 5];
let partitions = partition_by(&numbers, |x| *x);
assert_eq!(
partitions,
vec![vec![3, 3], vec![1, 1], vec![2, 2], vec![4], vec![5]]
);
}
#[test]
fn test_partition_by_with_mixed_types() {
let items = vec![
Item {
id: 1,
value: "one".to_string(),
},
Item {
id: 2,
value: "two".to_string(),
},
Item {
id: 1,
value: "one".to_string(),
},
Item {
id: 3,
value: "three".to_string(),
},
];
let partitions = partition_by(&items, |item| item.id);
assert_eq!(
partitions,
vec![
vec![
Item {
id: 1,
value: "one".to_string()
},
Item {
id: 1,
value: "one".to_string()
},
],
vec![Item {
id: 2,
value: "two".to_string()
},],
vec![Item {
id: 3,
value: "three".to_string()
},],
]
);
}
#[test]
fn test_partition_by_with_optionals() {
let collection = vec![Some(1), None, Some(2), Some(1), None, Some(3), Some(2)];
let partitions = partition_by(&collection, |x| x.clone());
assert_eq!(
partitions,
vec![
vec![Some(1), Some(1)],
vec![None, None],
vec![Some(2), Some(2)],
vec![Some(3)],
]
);
}
#[test]
fn test_partition_by_with_nan_floats() {
let float_collection = vec![std::f64::NAN, 2.2, std::f64::NAN, 4.4, std::f64::NAN];
let partitions = partition_by(&float_collection, |x| x.is_nan());
// All NaNs should be grouped under `true` and others under `false`
assert_eq!(partitions.len(), 2);
// Identify which partition is NaNs and which is non-NaNs
let mut nan_partition = false;
let mut non_nan_partition = false;
for partition in partitions {
if partition.iter().all(|x| x.is_nan()) {
assert!(!nan_partition, "NaN group already exists");
nan_partition = true;
assert_eq!(partition.len(), 3);
} else if partition.iter().all(|x| !x.is_nan()) {
assert!(!non_nan_partition, "Non-NaN group already exists");
non_nan_partition = true;
assert_eq!(partition, vec![2.2, 4.4]);
} else {
panic!("Partition contains both NaN and non-NaN values");
}
}
assert!(nan_partition, "NaN group was not found");
assert!(non_nan_partition, "Non-NaN group was not found");
}
}