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/// Apply a function to each item in a collection, filtering and transforming items based on a callback.
///
/// This function iterates over a collection and applies the provided `callback` function
/// to each item along with its index. If the callback returns `(R, true)`, the transformed
/// value `R` is included in the resulting vector.
///
/// # Arguments
/// * `collection` - A slice of items.
/// * `callback` - A function that takes a reference to an item and its index, returning a tuple `(R, bool)`
/// where `R` is the transformed value and `bool` indicates whether to include it.
///
/// # Returns
/// * `Vec<R>` - A vector containing the transformed items that passed the callback's predicate.
///
/// # Examples
/// ```rust
/// use lowdash::filter_map;
/// let numbers = vec![1, 2, 3, 4, 5];
/// // Double even numbers
/// let result = filter_map(&numbers, |x, _| {
/// if *x % 2 == 0 {
/// (x * 2, true)
/// } else {
/// (0, false)
/// }
/// });
/// assert_eq!(result, vec![4, 8]);
/// ```
///
/// ```rust
/// use lowdash::filter_map;
///
/// #[derive(Debug, PartialEq)]
/// 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: "Carol".to_string(), age: 35 },
/// ];
///
/// // Extract names of people older than 28
/// let names: Vec<String> = filter_map(&people, |p, _| {
/// if p.age > 28 {
/// (p.name.clone(), true)
/// } else {
/// (String::new(), false)
/// }
/// });
/// assert_eq!(names, vec!["Bob".to_string(), "Carol".to_string()]);
/// ```
pub fn filter_map<T, R, F>(collection: &[T], callback: F) -> Vec<R>
where
F: Fn(&T, usize) -> (R, bool),
{
let mut result = Vec::new();
for (index, item) in collection.iter().enumerate() {
let (mapped, include) = callback(item, index);
if include {
result.push(mapped);
}
}
result
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_filter_map_double_evens() {
let numbers = vec![1, 2, 3, 4, 5];
let result = filter_map(&numbers, |x, _| {
if *x % 2 == 0 {
(*x * 2, true)
} else {
(0, false)
}
});
assert_eq!(result, vec![4, 8]);
}
#[test]
fn test_filter_map_with_index() {
let numbers = vec![10, 20, 30, 40];
let result = filter_map(&numbers, |x, index| {
if index % 2 == 0 {
(*x + index as i32 * 10, true)
} else {
(0, false)
}
});
let expected = vec![10, 50]; // Corrected expected values
assert_eq!(result, expected);
}
#[test]
fn test_filter_map_strings_to_lengths() {
let strings = vec!["apple", "banana", "cherry", "date"];
let lengths = filter_map(&strings, |s, _| {
if s.len() > 5 {
(s.len(), true)
} else {
(0, false)
}
});
assert_eq!(lengths, vec![6, 6]);
}
#[test]
fn test_filter_map_structs() {
#[derive(Debug, PartialEq)]
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: "Carol".to_string(),
age: 35,
},
];
let ages: Vec<u32> = filter_map(&people, |p, _| {
if p.age > 28 {
(p.age, true)
} else {
(0, false)
}
});
assert_eq!(ages, vec![30, 35]);
}
#[test]
fn test_filter_map_empty_collection() {
let empty: Vec<i32> = vec![];
let result = filter_map(&empty, |x, _| (*x * 2, true));
let expected: Vec<i32> = vec![];
assert_eq!(result, expected);
}
#[test]
fn test_filter_map_with_floats() {
let float_collection = vec![1.1, 2.2, 3.3, 4.4];
let result = filter_map(&float_collection, |x, _| {
if *x > 2.2 {
(*x * 1.5, true)
} else {
(0.0, false)
}
});
let expected: Vec<f64> = vec![4.95, 6.6];
let epsilon: f64 = 1e-10;
// Ensure both vectors have the same length
assert_eq!(
result.len(),
expected.len(),
"Result and expected vectors have different lengths"
);
// Iterate through both vectors and compare each pair of elements within the tolerance
for (res, exp) in result.iter().zip(expected.iter()) {
assert!(
(*res - *exp).abs() < epsilon,
"Expected {}, but got {}",
exp,
res
);
}
}
#[test]
fn test_filter_map_with_negative_numbers() {
let numbers: Vec<i32> = vec![-1, -2, -3];
let result: Vec<i32> =
filter_map(
&numbers,
|x, _| {
if *x < 0 {
(x.abs(), true)
} else {
(0, false)
}
},
);
assert_eq!(result, vec![1, 2, 3]);
}
#[test]
fn test_filter_map_with_complex_logic() {
let numbers = vec![1, 2, 3, 4, 5];
let result = filter_map(&numbers, |x, index| {
if *x % 2 != 0 {
(x * (index + 1) as i32, true)
} else {
(0, false)
}
});
assert_eq!(result, vec![1, 9, 25]);
}
#[test]
fn test_filter_map_all_included() {
let numbers = vec![1, 2, 3];
let result = filter_map(&numbers, |x, _| (*x, true));
assert_eq!(result, vec![1, 2, 3]);
}
#[test]
fn test_filter_map_all_excluded() {
let numbers = vec![1, 2, 3];
let result = filter_map(&numbers, |_, _| (0, false));
let expected: Vec<i32> = vec![];
assert_eq!(result, expected);
}
}