ferray_strings/
concat.rs

1// ferray-strings: Concatenation and repetition operations (REQ-3, REQ-4)
2//
3// Implements add (elementwise concat with broadcasting) and multiply (repeat).
4
5use ferray_core::dimension::{Dimension, IxDyn};
6use ferray_core::error::FerrayResult;
7
8use crate::string_array::{StringArray, broadcast_binary};
9
10/// Elementwise string concatenation with broadcasting.
11///
12/// Concatenates corresponding elements of `a` and `b`. If shapes differ,
13/// NumPy-style broadcasting is applied (e.g., a scalar string is broadcast
14/// against an array).
15///
16/// The result is always a dynamic-rank `StringArray<IxDyn>`.
17///
18/// # Errors
19/// Returns `FerrayError::BroadcastFailure` if shapes are incompatible.
20pub fn add<Da: Dimension, Db: Dimension>(
21    a: &StringArray<Da>,
22    b: &StringArray<Db>,
23) -> FerrayResult<StringArray<IxDyn>> {
24    let (out_shape, pairs) = broadcast_binary(a, b)?;
25    let a_data = a.as_slice();
26    let b_data = b.as_slice();
27
28    let data: Vec<String> = pairs
29        .iter()
30        .map(|&(ia, ib)| format!("{}{}", a_data[ia], b_data[ib]))
31        .collect();
32
33    StringArray::from_vec(IxDyn::new(&out_shape), data)
34}
35
36/// Repeat each string element `n` times.
37///
38/// # Errors
39/// Returns an error if the internal array construction fails.
40pub fn multiply<D: Dimension>(a: &StringArray<D>, n: usize) -> FerrayResult<StringArray<D>> {
41    a.map(|s| s.repeat(n))
42}
43
44#[cfg(test)]
45mod tests {
46    use super::*;
47    use crate::string_array::array;
48
49    #[test]
50    fn test_add_same_shape() {
51        let a = array(&["hello", "foo"]).unwrap();
52        let b = array(&[" world", " bar"]).unwrap();
53        let c = add(&a, &b).unwrap();
54        assert_eq!(c.as_slice(), &["hello world", "foo bar"]);
55    }
56
57    #[test]
58    fn test_add_broadcast_scalar() {
59        // AC-2: strings::add broadcasts a scalar string against an array correctly
60        let a = array(&["hello", "world"]).unwrap();
61        let b = array(&["!"]).unwrap();
62        let c = add(&a, &b).unwrap();
63        assert_eq!(c.as_slice(), &["hello!", "world!"]);
64    }
65
66    #[test]
67    fn test_add_broadcast_scalar_left() {
68        let a = array(&[">> "]).unwrap();
69        let b = array(&["hello", "world"]).unwrap();
70        let c = add(&a, &b).unwrap();
71        assert_eq!(c.as_slice(), &[">> hello", ">> world"]);
72    }
73
74    #[test]
75    fn test_add_incompatible_shapes() {
76        let a = array(&["a", "b", "c"]).unwrap();
77        let b = array(&["x", "y"]).unwrap();
78        assert!(add(&a, &b).is_err());
79    }
80
81    #[test]
82    fn test_multiply() {
83        let a = array(&["ab", "cd"]).unwrap();
84        let b = multiply(&a, 3).unwrap();
85        assert_eq!(b.as_slice(), &["ababab", "cdcdcd"]);
86    }
87
88    #[test]
89    fn test_multiply_zero() {
90        let a = array(&["hello"]).unwrap();
91        let b = multiply(&a, 0).unwrap();
92        assert_eq!(b.as_slice(), &[""]);
93    }
94
95    #[test]
96    fn test_multiply_one() {
97        let a = array(&["hello"]).unwrap();
98        let b = multiply(&a, 1).unwrap();
99        assert_eq!(b.as_slice(), &["hello"]);
100    }
101}
ferray_strings/concat.rs

ferray_strings/
concat.rs
