Add utility method to iterate a shape by column #21
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Sometimes it is required that we iterate over the same elements of different arrays. An example of this is pointwise operations where the views of the two operands might be different, and we can't simply use the same index on the underlying storages.
ag14774
reviewed
Dec 9, 2021
mathoxide-lib/src/utils.rs
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| fn next(&mut self) -> Option<Self::Item> { | ||
| if self.current >= self.numel { | ||
| None | ||
| } else { | ||
| let v = inverse_translate(self.current, &self.shape); | ||
| self.current += 1; | ||
| Some(v) | ||
| } | ||
| } |
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Suggested change
| fn next(&mut self) -> Option<Self::Item> { | |
| if self.current >= self.numel { | |
| None | |
| } else { | |
| let v = inverse_translate(self.current, &self.shape); | |
| self.current += 1; | |
| Some(v) | |
| } | |
| } | |
| fn next(&mut self) -> Option<Self::Item> { | |
| let ndim = self.shape.len(); | |
| let mut carry: usize = 1; | |
| let mut pointer: usize = 0; | |
| while carry == 1 && pointer < ndim { | |
| self.current[ndim - pointer - 1] += carry; | |
| carry = self.current[ndim - pointer - 1] / self.shape[ndim - pointer - 1]; | |
| self.current[ndim - pointer - 1] %= self.shape[ndim - pointer - 1]; | |
| pointer += 1; | |
| } | |
| if carry == 1 { | |
| None | |
| } | |
| else { | |
| Some(self.current.clone()) | |
| } | |
| } |
This is another way to do it. self.current here is also a Vec and numel is not required. Keep whichever you think is easier to read/more idiomatic for rust. Disclaimer: the code above is not tested
mathoxide-lib/src/utils.rs
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| fn inverse_translate<Shape: AsRef<[usize]>>(idx: usize, shape: Shape) -> Vec<usize> { | ||
| shape.as_ref().iter().rev().scan((1, 0), |(divisor, remainder), e| { | ||
| let prev_div = *divisor; | ||
| *divisor *= e; | ||
| let res = ((idx - *remainder) % *divisor) / prev_div; | ||
| *remainder += res; | ||
| Some(res) | ||
| }).collect() | ||
| } |
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If I were to keep the current approach I would precompute the the products of the shape during the construction of the iterator e.g if shape=[1,2,3], precompute suffix_product=[6,6,3]. Then you don't actually need to iterate here in reverse once you have the suffix_product precomputed
mathoxide-lib/src/utils.rs
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| } | ||
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| pub fn iterate_by_column<Shape: AsRef<[usize]>>(shape: &Shape) -> ByRowIterator { |
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Maybe the name could be iterate_row_major. By column could be confused as going over the whole columns one by one in a column major order
ag14774
reviewed
Dec 10, 2021
mathoxide-lib/src/utils.rs
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| } | ||
| } | ||
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| pub fn by_column<Shape>(shape: &'a Shape) -> Self |
ag14774
approved these changes
Dec 10, 2021
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Sometimes it is required that we iterate over the same elements of different
arrays. An example of this is pointwise operations where the views of
the two operands might be different, and we can't simply use the same index
on the underlying storages.
This PR is needed to resolve #2