arrow_ord/
partition.rs

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4// regarding copyright ownership.  The ASF licenses this file
5// to you under the Apache License, Version 2.0 (the
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8//
9//   http://www.apache.org/licenses/LICENSE-2.0
10//
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14// KIND, either express or implied.  See the License for the
15// specific language governing permissions and limitations
16// under the License.
17
18//! Defines partition kernel for `ArrayRef`
19
20use std::ops::Range;
21
22use arrow_array::{Array, ArrayRef};
23use arrow_buffer::BooleanBuffer;
24use arrow_schema::{ArrowError, SortOptions};
25
26use crate::cmp::{distinct, supports_distinct};
27use crate::ord::make_comparator;
28
29/// A computed set of partitions, see [`partition`]
30#[derive(Debug, Clone)]
31pub struct Partitions(Option<BooleanBuffer>);
32
33impl Partitions {
34    /// Returns the range of each partition
35    ///
36    /// Consecutive ranges will be contiguous: i.e [`(a, b)` and `(b, c)`], and
37    /// `start = 0` and `end = self.len()` for the first and last range respectively
38    pub fn ranges(&self) -> Vec<Range<usize>> {
39        let Some(boundaries) = &self.0 else {
40            return vec![];
41        };
42
43        let mut out = vec![];
44        let mut current = 0;
45        for idx in boundaries.set_indices() {
46            let t = current;
47            current = idx + 1;
48            out.push(t..current)
49        }
50        let last = boundaries.len() + 1;
51        if current != last {
52            out.push(current..last)
53        }
54        out
55    }
56
57    /// Returns the number of partitions
58    pub fn len(&self) -> usize {
59        match &self.0 {
60            Some(b) => b.count_set_bits() + 1,
61            None => 0,
62        }
63    }
64
65    /// Returns true if this contains no partitions
66    pub fn is_empty(&self) -> bool {
67        self.0.is_none()
68    }
69}
70
71/// Given a list of lexicographically sorted columns, computes the [`Partitions`],
72/// where a partition consists of the set of consecutive rows with equal values
73///
74/// Returns an error if no columns are specified or all columns do not
75/// have the same number of rows.
76///
77/// # Example:
78///
79/// For example, given columns `x`, `y` and `z`, calling
80/// [`partition`]`(values, (x, y))` will divide the
81/// rows into ranges where the values of `(x, y)` are equal:
82///
83/// ```text
84/// ┌ ─ ┬───┬ ─ ─┌───┐─ ─ ┬───┬ ─ ─ ┐
85///     │ 1 │    │ 1 │    │ A │        Range: 0..1 (x=1, y=1)
86/// ├ ─ ┼───┼ ─ ─├───┤─ ─ ┼───┼ ─ ─ ┤
87///     │ 1 │    │ 2 │    │ B │
88/// │   ├───┤    ├───┤    ├───┤     │
89///     │ 1 │    │ 2 │    │ C │        Range: 1..4 (x=1, y=2)
90/// │   ├───┤    ├───┤    ├───┤     │
91///     │ 1 │    │ 2 │    │ D │
92/// ├ ─ ┼───┼ ─ ─├───┤─ ─ ┼───┼ ─ ─ ┤
93///     │ 2 │    │ 1 │    │ E │        Range: 4..5 (x=2, y=1)
94/// ├ ─ ┼───┼ ─ ─├───┤─ ─ ┼───┼ ─ ─ ┤
95///     │ 3 │    │ 1 │    │ F │        Range: 5..6 (x=3, y=1)
96/// └ ─ ┴───┴ ─ ─└───┘─ ─ ┴───┴ ─ ─ ┘
97///
98///       x        y        z     partition(&[x, y])
99/// ```
100///
101/// # Example Code
102///
103/// ```
104/// # use std::{sync::Arc, ops::Range};
105/// # use arrow_array::{RecordBatch, Int64Array, StringArray, ArrayRef};
106/// # use arrow_ord::sort::{SortColumn, SortOptions};
107/// # use arrow_ord::partition::partition;
108/// let batch = RecordBatch::try_from_iter(vec![
109///     ("x", Arc::new(Int64Array::from(vec![1, 1, 1, 1, 2, 3])) as ArrayRef),
110///     ("y", Arc::new(Int64Array::from(vec![1, 2, 2, 2, 1, 1])) as ArrayRef),
111///     ("z", Arc::new(StringArray::from(vec!["A", "B", "C", "D", "E", "F"])) as ArrayRef),
112/// ]).unwrap();
113///
114/// // Partition on first two columns
115/// let ranges = partition(&batch.columns()[..2]).unwrap().ranges();
116///
117/// let expected = vec![
118///     (0..1),
119///     (1..4),
120///     (4..5),
121///     (5..6),
122/// ];
123///
124/// assert_eq!(ranges, expected);
125/// ```
126pub fn partition(columns: &[ArrayRef]) -> Result<Partitions, ArrowError> {
127    if columns.is_empty() {
128        return Err(ArrowError::InvalidArgumentError(
129            "Partition requires at least one column".to_string(),
130        ));
131    }
132    let num_rows = columns[0].len();
133    if columns.iter().any(|item| item.len() != num_rows) {
134        return Err(ArrowError::InvalidArgumentError(
135            "Partition columns have different row counts".to_string(),
136        ));
137    }
138
139    match num_rows {
140        0 => return Ok(Partitions(None)),
141        1 => return Ok(Partitions(Some(BooleanBuffer::new_unset(0)))),
142        _ => {}
143    }
144
145    let acc = find_boundaries(&columns[0])?;
146    let acc = columns
147        .iter()
148        .skip(1)
149        .try_fold(acc, |acc, c| find_boundaries(c.as_ref()).map(|b| &acc | &b))?;
150
151    Ok(Partitions(Some(acc)))
152}
153
154/// Returns a mask with bits set whenever the value or nullability changes
155fn find_boundaries(v: &dyn Array) -> Result<BooleanBuffer, ArrowError> {
156    let slice_len = v.len() - 1;
157    let v1 = v.slice(0, slice_len);
158    let v2 = v.slice(1, slice_len);
159
160    if supports_distinct(v.data_type()) {
161        return Ok(distinct(&v1, &v2)?.values().clone());
162    }
163    // Given that we're only comparing values, null ordering in the input or
164    // sort options do not matter.
165    let cmp = make_comparator(&v1, &v2, SortOptions::default())?;
166    Ok((0..slice_len).map(|i| !cmp(i, i).is_eq()).collect())
167}
168
169#[cfg(test)]
170mod tests {
171    use std::sync::Arc;
172
173    use super::*;
174    use arrow_array::*;
175    use arrow_schema::DataType;
176
177    #[test]
178    fn test_partition_empty() {
179        let err = partition(&[]).unwrap_err();
180        assert_eq!(
181            err.to_string(),
182            "Invalid argument error: Partition requires at least one column"
183        );
184    }
185
186    #[test]
187    fn test_partition_unaligned_rows() {
188        let input = vec![
189            Arc::new(Int64Array::from(vec![None, Some(-1)])) as _,
190            Arc::new(StringArray::from(vec![Some("foo")])) as _,
191        ];
192        let err = partition(&input).unwrap_err();
193        assert_eq!(
194            err.to_string(),
195            "Invalid argument error: Partition columns have different row counts"
196        )
197    }
198
199    #[test]
200    fn test_partition_small() {
201        let results = partition(&[
202            Arc::new(Int32Array::new(vec![].into(), None)) as _,
203            Arc::new(Int32Array::new(vec![].into(), None)) as _,
204            Arc::new(Int32Array::new(vec![].into(), None)) as _,
205        ])
206        .unwrap();
207        assert_eq!(results.len(), 0);
208        assert!(results.is_empty());
209
210        let results = partition(&[
211            Arc::new(Int32Array::from(vec![1])) as _,
212            Arc::new(Int32Array::from(vec![1])) as _,
213        ])
214        .unwrap()
215        .ranges();
216        assert_eq!(results.len(), 1);
217        assert_eq!(results[0], 0..1);
218    }
219
220    #[test]
221    fn test_partition_single_column() {
222        let a = Int64Array::from(vec![1, 2, 2, 2, 2, 2, 2, 2, 9]);
223        let input = vec![Arc::new(a) as _];
224        assert_eq!(
225            partition(&input).unwrap().ranges(),
226            vec![(0..1), (1..8), (8..9)],
227        );
228    }
229
230    #[test]
231    fn test_partition_all_equal_values() {
232        let a = Int64Array::from_value(1, 1000);
233        let input = vec![Arc::new(a) as _];
234        assert_eq!(partition(&input).unwrap().ranges(), vec![(0..1000)]);
235    }
236
237    #[test]
238    fn test_partition_all_null_values() {
239        let input = vec![
240            new_null_array(&DataType::Int8, 1000),
241            new_null_array(&DataType::UInt16, 1000),
242        ];
243        assert_eq!(partition(&input).unwrap().ranges(), vec![(0..1000)]);
244    }
245
246    #[test]
247    fn test_partition_unique_column_1() {
248        let input = vec![
249            Arc::new(Int64Array::from(vec![None, Some(-1)])) as _,
250            Arc::new(StringArray::from(vec![Some("foo"), Some("bar")])) as _,
251        ];
252        assert_eq!(partition(&input).unwrap().ranges(), vec![(0..1), (1..2)],);
253    }
254
255    #[test]
256    fn test_partition_unique_column_2() {
257        let input = vec![
258            Arc::new(Int64Array::from(vec![None, Some(-1), Some(-1)])) as _,
259            Arc::new(StringArray::from(vec![
260                Some("foo"),
261                Some("bar"),
262                Some("apple"),
263            ])) as _,
264        ];
265        assert_eq!(
266            partition(&input).unwrap().ranges(),
267            vec![(0..1), (1..2), (2..3),],
268        );
269    }
270
271    #[test]
272    fn test_partition_non_unique_column_1() {
273        let input = vec![
274            Arc::new(Int64Array::from(vec![None, Some(-1), Some(-1), Some(1)])) as _,
275            Arc::new(StringArray::from(vec![
276                Some("foo"),
277                Some("bar"),
278                Some("bar"),
279                Some("bar"),
280            ])) as _,
281        ];
282        assert_eq!(
283            partition(&input).unwrap().ranges(),
284            vec![(0..1), (1..3), (3..4),],
285        );
286    }
287
288    #[test]
289    fn test_partition_masked_nulls() {
290        let input = vec![
291            Arc::new(Int64Array::new(vec![1; 9].into(), None)) as _,
292            Arc::new(Int64Array::new(
293                vec![1, 1, 2, 2, 2, 3, 3, 3, 3].into(),
294                Some(vec![false, true, true, true, true, false, false, true, false].into()),
295            )) as _,
296            Arc::new(Int64Array::new(
297                vec![1, 1, 2, 2, 2, 2, 2, 3, 7].into(),
298                Some(vec![true, true, true, true, false, true, true, true, false].into()),
299            )) as _,
300        ];
301
302        assert_eq!(
303            partition(&input).unwrap().ranges(),
304            vec![(0..1), (1..2), (2..4), (4..5), (5..7), (7..8), (8..9)],
305        );
306    }
307
308    #[test]
309    fn test_partition_run_end_encoded() {
310        let run_ends = Int32Array::from(vec![2, 3, 5]);
311        let values = StringArray::from(vec!["x", "y", "x"]);
312        let ree = RunArray::try_new(&run_ends, &values).unwrap();
313        // logical: ["x", "x", "y", "x", "x"]
314        let input = vec![Arc::new(ree) as _];
315        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5],);
316    }
317
318    #[test]
319    fn test_partition_nested_run_end_encoded() {
320        // Inner REE (values of the outer): run_ends [1, 2, 3], values ["x", "y", "x"]
321        // logical length 3: ["x", "y", "x"]
322        let inner_run_ends = Int32Array::from(vec![1, 2, 3]);
323        let inner_values = StringArray::from(vec!["x", "y", "x"]);
324        let inner_ree = RunArray::try_new(&inner_run_ends, &inner_values).unwrap();
325
326        // Outer REE: run_ends [2, 3, 5], values = inner_ree (length 3)
327        // logical: rows 0,1 → inner[0]="x", row 2 → inner[1]="y", rows 3,4 → inner[2]="x"
328        // = ["x", "x", "y", "x", "x"]
329        let outer_run_ends = Int32Array::from(vec![2, 3, 5]);
330        let outer_ree = RunArray::try_new(&outer_run_ends, &inner_ree).unwrap();
331
332        let input = vec![Arc::new(outer_ree) as ArrayRef];
333        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5]);
334    }
335
336    #[test]
337    fn test_partition_ree_with_dictionary_values() {
338        // Dictionary values: keys [0, 1, 0], dict ["x", "y"] → logical ["x", "y", "x"]
339        let dict_values = StringArray::from(vec!["x", "y"]);
340        let keys = Int32Array::from(vec![0, 1, 0]);
341        let dict = DictionaryArray::try_new(keys, Arc::new(dict_values)).unwrap();
342
343        // REE wrapping dict: run_ends [2, 3, 5] → logical [dict[0], dict[0], dict[1], dict[2], dict[2]]
344        // = ["x", "x", "y", "x", "x"]
345        let run_ends = Int32Array::from(vec![2, 3, 5]);
346        let ree = RunArray::try_new(&run_ends, &dict).unwrap();
347        let input = vec![Arc::new(ree) as ArrayRef];
348        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5],);
349    }
350
351    #[test]
352    fn test_partition_dictionary() {
353        let values = StringArray::from(vec!["x", "y"]);
354        let keys = Int32Array::from(vec![0, 0, 1, 0, 0]);
355        let dict = DictionaryArray::try_new(keys, Arc::new(values)).unwrap();
356        // logical: ["x", "x", "y", "x", "x"]
357        let input = vec![Arc::new(dict) as _];
358        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5],);
359    }
360
361    #[test]
362    fn test_partition_nested_dictionary() {
363        let inner_values = StringArray::from(vec!["x", "y"]);
364        let inner_keys = Int32Array::from(vec![0, 1, 0]);
365        let inner_dict = DictionaryArray::try_new(inner_keys, Arc::new(inner_values)).unwrap();
366
367        // Outer dict keys index into inner dict's logical values: ["x", "y", "x"]
368        // keys [0, 0, 1, 2, 2] → logical ["x", "x", "y", "x", "x"]
369        let outer_keys = Int32Array::from(vec![0, 0, 1, 2, 2]);
370        let outer_dict = DictionaryArray::try_new(outer_keys, Arc::new(inner_dict)).unwrap();
371        let input = vec![Arc::new(outer_dict) as ArrayRef];
372        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5],);
373    }
374
375    #[test]
376    fn test_partition_dictionary_with_ree_values() {
377        // REE values: run_ends [2, 3], values ["x", "y"] → logical ["x", "x", "y"]
378        let run_ends = Int32Array::from(vec![2, 3]);
379        let str_values = StringArray::from(vec!["x", "y"]);
380        let ree = RunArray::try_new(&run_ends, &str_values).unwrap();
381
382        // Dictionary keys index into the REE's logical values
383        // keys [0, 0, 2, 0, 0] → logical ["x", "x", "y", "x", "x"]
384        let keys = Int32Array::from(vec![0, 0, 2, 0, 0]);
385        let dict = DictionaryArray::try_new(keys, Arc::new(ree)).unwrap();
386        let input = vec![Arc::new(dict) as ArrayRef];
387        assert_eq!(partition(&input).unwrap().ranges(), vec![0..2, 2..3, 3..5],);
388    }
389
390    #[test]
391    fn test_partition_nested() {
392        let input = vec![
393            Arc::new(
394                StructArray::try_from(vec![(
395                    "f1",
396                    Arc::new(Int64Array::from(vec![
397                        None,
398                        None,
399                        Some(1),
400                        Some(2),
401                        Some(2),
402                        Some(2),
403                        Some(3),
404                        Some(4),
405                    ])) as _,
406                )])
407                .unwrap(),
408            ) as _,
409            Arc::new(Int64Array::from(vec![1, 1, 1, 2, 3, 3, 3, 4])) as _,
410        ];
411        assert_eq!(
412            partition(&input).unwrap().ranges(),
413            vec![0..2, 2..3, 3..4, 4..6, 6..7, 7..8]
414        )
415    }
416}
arrow_ord/partition.rs

arrow_ord/
partition.rs
