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Add support for negative range indexing on tensors #783

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Add support for negative range indexing on tensors #783

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59 changes: 51 additions & 8 deletions src/tensor/index.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -304,22 +304,65 @@ impl Tensor {
curr_idx, // not advanced because select() squeezes dimension
),
Narrow(start, end) => {

let positive_index = |i: &i64, dim_len| {
if *i < 0 { dim_len + *i } else { *i }
};

if let Some((start, length)) = match (start, end) {
(Unbounded, Unbounded) => None,
(Included(start), Unbounded) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
Some((*start, dim_len - *start))
let start = positive_index(start, dim_len);

Some((start, dim_len - start))
}
(Excluded(start), Unbounded) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
Some((*start + 1, dim_len - *start - 1))
let start = positive_index(start, dim_len);

Some((start + 1, dim_len - start - 1))
}
(Unbounded, Included(end)) => Some((0, *end + 1)),
(Unbounded, Excluded(end)) => Some((0, *end)),
(Included(start), Included(end)) => Some((*start, *end - *start + 1)),
(Included(start), Excluded(end)) => Some((*start, *end - *start)),
(Excluded(start), Included(end)) => Some((*start + 1, *end - *start)),
(Excluded(start), Excluded(end)) => Some((*start + 1, *end - *start - 1)),
(Unbounded, Included(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let end = positive_index(end, dim_len);

Some((0, end + 1))
},
(Unbounded, Excluded(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let end = positive_index(end, dim_len);

Some((0, end))
},
(Included(start), Included(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let start = positive_index(start, dim_len);
let end = positive_index(end, dim_len);

Some((start, end - start + 1))
},
(Included(start), Excluded(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let start = positive_index(start, dim_len);
let end = positive_index(end, dim_len);

Some((start, end - start))
},
(Excluded(start), Included(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let start = positive_index(start, dim_len);
let end = positive_index(end, dim_len);

Some((start + 1, end - start))
},
(Excluded(start), Excluded(end)) => {
let dim_len = curr_tensor.size()[curr_idx as usize];
let start = positive_index(start, dim_len);
let end = positive_index(end, dim_len);

Some((start + 1, end - start - 1))
},
} {
(curr_tensor.narrow(curr_idx, start, length.max(0)), curr_idx + 1)
} else {
Expand Down
21 changes: 21 additions & 0 deletions tests/tensor_indexing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,10 @@ fn range_index() {
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[3, 4, 5, 6, 7, 8]);

let result = tensor.i(-4..-2);
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[0, 1, 2, 3, 4, 5]);

// RangeFull
let tensor = Tensor::arange_start(0, 2 * 3, opt).view([2, 3]);
let result = tensor.i(..);
Expand All @@ -45,18 +49,31 @@ fn range_index() {
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[6, 7, 8, 9, 10, 11]);

let result = tensor.i(-1..);
assert_eq!(result.size(), &[1, 3]);
assert_eq!(vec_i64_from(&result), &[9, 10, 11]);

// RangeTo
let tensor = Tensor::arange_start(0, 4 * 3, opt).view([4, 3]);
let result = tensor.i(..2);
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[0, 1, 2, 3, 4, 5]);

let result = tensor.i(..-3);
assert_eq!(result.size(), &[1, 3]);
assert_eq!(vec_i64_from(&result), &[0, 1, 2]);

// RangeInclusive
let tensor = Tensor::arange_start(0, 4 * 3, opt).view([4, 3]);
let result = tensor.i(1..=2);
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[3, 4, 5, 6, 7, 8]);

let (start, end) = (1, -2);
let result = tensor.i(start..=end);
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[3, 4, 5, 6, 7, 8]);

// RangeTo
let tensor = Tensor::arange_start(0, 4 * 3, opt).view([4, 3]);
let result = tensor.i(..1);
Expand All @@ -69,6 +86,10 @@ fn range_index() {
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[0, 1, 2, 3, 4, 5]);

let result = tensor.i(..=-3);
assert_eq!(result.size(), &[2, 3]);
assert_eq!(vec_i64_from(&result), &[0, 1, 2, 3, 4, 5]);

// Negative Cases
//
// Rust considers both `0..0` and `1..0` to be valid, empty ranges.
Expand Down