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[GitHub] [arrow-rs] HaoYang670 opened a new pull request, #1529: update the doc of `substring`
HaoYang670 opened a new pull request, #1529:
URL: https://github.com/apache/arrow-rs/pull/1529
Signed-off-by: remzi <13...@gmail.com>
# Which issue does this PR close?
<!---
We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes #123` indicates that this PR will close issue #123.
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Closes #1478.
# Rationale for this change
Tell users the `pitfall` of `substring` function.
# Are there any user-facing changes?
Doc is updated.
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: Improve doc string for `substring` kernel
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846767453
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
Hi @alamb . I have filed as epic issue: #1531 .
Please review.
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[GitHub] [arrow-rs] codecov-commenter commented on pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
codecov-commenter commented on PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#issuecomment-1092819930
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[GitHub] [arrow-rs] alamb commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
alamb commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846377282
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
🤔 Is it worth a ticket to add utf8 validation to this kernel? It should be straightforward, but will likely slow it down.
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
Review Comment:
```suggestion
/// This function **might** return in invalid utf-8 format if the character length falls on a non-utf8 boundary.
```
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846528223
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
By the way, is it necessary to mark `substring` unsafe?
Besides, we could implement a safe version of `substring` and also `substring_by_char`:
| name | Safety | Performance |
|--------------|-----------|------------|
| unsafe substring_unckecked | user should make sure valid utf8 substrings can be gotten with `start` and `length` | fast |
| substring_checked | None | slow |
| substring_by_char | None | slow |
**Users should always make sure all values of the input string array are in valid utf-8 format.**
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846528223
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
By the way, is it necessary to mark `substring` unsafe?
Besides, we could implement a safe version of `substring` and also `substring_by_char`:
| name | Safety | Performance |
|--------------|-----------|------------|
| unsafe substring_unckecked | user should make sure valid utf8 substrings can be gotten with `start` and `length` | fast |
| substring_checked | None | slow |
| substring_by_char | None | slow |
**Users should always make sure all values of the input string array are in valid utf-8 format.**
This will improve the safety of the `substring` kernel, but break the public API.
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846606569
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
Also, Arrow2 has implemented `substring` for binary array. I am not sure whether we need to do it.
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[GitHub] [arrow-rs] alamb merged pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
alamb merged PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846698152
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
We could also add support for `ListArray` and `FixedSizedListArray`
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[GitHub] [arrow-rs] alamb commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
alamb commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846762535
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
@HaoYang670 I think these are all good ideas (making safe / unsafe versions, and adding substring for binary etc). I would be happy to create tickets for them if that would help
If we are going to change the substring kernel, I suggest we do the following to follow Rust's safe-by-defauly mantra:
| name | Safety | Performance | Notes |
|--------------|-----------|------------|---------|
| unsafe substring_bytes_unchecked | unsafe | fast| what is currently called `substring` - user should make sure valid utf8 substrings can be gotten with `start` and `length` | fast |
| substring_bytes | safe | slow | Implement substring by bytes - throws error of invalid utf-8 sequence is created
| substring | safe | slow | Implement substring by char, ensuring all substrings are utf-8
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
@HaoYang670 I think these are all good ideas (making safe / unsafe versions, and adding substring for binary etc). I would be happy to create tickets for them if that would help
If we are going to change the substring kernel, I suggest we do the following to follow Rust's safe-by-default mantra:
| name | Safety | Performance | Notes |
|--------------|-----------|------------|---------|
| unsafe substring_bytes_unchecked | unsafe | fast| what is currently called `substring` - user should make sure valid utf8 substrings can be gotten with `start` and `length` | fast |
| substring_bytes | safe | slow | Implement substring by bytes - throws error of invalid utf-8 sequence is created
| substring | safe | slow | Implement substring by char, ensuring all substrings are utf-8
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846528223
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
By the way, we could add another function called `substring_by_char` which could be safe but slow.
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846525769
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
I am afraid the time complexity will be changed. Currently, the time complexity is `O(length of offset buffer)`. Adding validation might increase the time complexity to `O(length of offset buffer + length of value buffer)` because we have to read every byte in the value buffer in the worst case:
https://github.com/apache/arrow-rs/blob/master/arrow/src/array/data.rs#L1090-L1112
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846525769
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
I am afraid the time complexity will be changed. Currently, the time complexity is `O(length of offset buffer)`. Adding validation might increase the time complexity to `O(length of offset buffer + length of value buffer)` because we have to read every byte in the value buffer in the worst case:
https://github.com/apache/arrow-rs/blob/master/arrow/src/array/data.rs#L925-L968
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846525769
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
I am afraid the time complexity will be changed. Currently, the time complexity is `O(length of offset buffer)`. Adding validation might increase the time complexity to `O(length of offset buffer + length of value buffer)` because we have to read every byte in the value buffer in the worst case.
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846698152
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
We could also add `substring` support for `ListArray`, `FixedSizeListArray` and `FixedSizeBinaryArray`
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[GitHub] [arrow-rs] HaoYang670 commented on a diff in pull request #1529: update the doc of `substring`
Posted by GitBox <gi...@apache.org>.
HaoYang670 commented on code in PR #1529:
URL: https://github.com/apache/arrow-rs/pull/1529#discussion_r846528223
##########
arrow/src/compute/kernels/substring.rs:
##########
@@ -94,8 +94,33 @@ fn generic_substring<OffsetSize: StringOffsetSizeTrait>(
Ok(make_array(data))
}
-/// Returns an ArrayRef with a substring starting from `start` and with optional length `length` of each of the elements in `array`.
-/// `start` can be negative, in which case the start counts from the end of the string.
+/// Returns an ArrayRef with substrings of all the elements in `array`.
+///
+/// # Arguments
+///
+/// * `start` - The start index of all substrings.
+/// If `start >= 0`, then count from the start of the string,
+/// otherwise count from the end of the string.
+///
+/// * `length`(option) - The length of all substrings.
+/// If `length` is `None`, then the substring is from `start` to the end of the string.
+///
+/// Attention: Both `start` and `length` are counted by byte, not by char.
+///
+/// # Warning
+///
+/// This function **might** return in invalid utf-8 format if strings contain chars whose codepoint > `0x007F`.
+/// ## Example of getting an invalid substring
+/// ```
+/// # use arrow::array::StringArray;
+/// # use arrow::compute::kernels::substring::substring;
+/// let array = StringArray::from(vec![Some("E=mc²")]);
+/// let result = substring(&array, -1, &None).unwrap();
+/// let result = result.as_any().downcast_ref::<StringArray>().unwrap();
+/// assert_eq!(result.value(0).as_bytes(), &[0x00B2]); // invalid utf-8 format
Review Comment:
By the way, is it necessary to mark `substring` unsafe?
Besides, we could implement a safe version of `substring` and also `substring_by_char`:
| name | Safety | Performance |
|--------------|-----------|------------|
| unsafe substring_unckecked | user should make sure valid utf8 substrings can be gotten with `start` and `length` | fast |
| substring_checked | None | slow |
| substring_by_char | None | slow |
**Users should always make sure all values of the input array are in valid utf-8 format.**
This will improve the safety of the `substring` kernel, but break the public API.
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