[GitHub] [arrow-rs] tustvold commented on a diff in pull request #2826: Convert rows to arrays (#2677)

[GitBox <gi...@apache.org>]

tustvold commented on code in PR #2826:
URL: https://github.com/apache/arrow-rs/pull/2826#discussion_r988722284


##########
arrow/src/row/dictionary.rs:
##########
@@ -0,0 +1,296 @@
+// Licensed to the Apache Software Foundation (ASF) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The ASF licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+use crate::compute::SortOptions;
+use crate::row::fixed::{FixedLengthEncoding, FromSlice, RawDecimal};
+use crate::row::interner::{Interned, OrderPreservingInterner};
+use arrow_array::builder::*;
+use arrow_array::cast::*;
+use arrow_array::types::*;
+use arrow_array::*;
+use arrow_buffer::{ArrowNativeType, MutableBuffer, ToByteSlice};
+use arrow_data::{ArrayData, ArrayDataBuilder};
+use arrow_schema::{ArrowError, DataType, IntervalUnit, TimeUnit};
+use std::collections::HashMap;
+
+/// Computes the dictionary mapping for the given dictionary values
+pub fn compute_dictionary_mapping(
+    interner: &mut OrderPreservingInterner,
+    values: &ArrayRef,
+) -> Result<Vec<Option<Interned>>, ArrowError> {
+    Ok(downcast_primitive_array! {
+        values => interner
+            .intern(values.iter().map(|x| x.map(|x| x.encode()))),
+        DataType::Binary => {
+            let iter = as_generic_binary_array::<i64>(values).iter();
+            interner.intern(iter)
+        }
+        DataType::LargeBinary => {
+            let iter = as_generic_binary_array::<i64>(values).iter();
+            interner.intern(iter)
+        }
+        DataType::Utf8 => {
+            let iter = as_string_array(values).iter().map(|x| x.map(|x| x.as_bytes()));
+            interner.intern(iter)
+        }
+        DataType::LargeUtf8 => {
+            let iter = as_largestring_array(values).iter().map(|x| x.map(|x| x.as_bytes()));
+            interner.intern(iter)
+        }
+        t => return Err(ArrowError::NotYetImplemented(format!("dictionary value {} is not supported", t))),
+    })
+}
+
+/// Decodes a string array from `rows` with the provided `options`
+///
+/// # Safety
+///
+/// `interner` must contain valid data for the provided `value_type`
+pub unsafe fn decode_dictionary<K: ArrowDictionaryKeyType>(
+    interner: &OrderPreservingInterner,
+    value_type: &DataType,
+    options: SortOptions,
+    rows: &mut [&[u8]],
+) -> Result<DictionaryArray<K>, ArrowError> {
+    let len = rows.len();
+    let mut dictionary: HashMap<Interned, K::Native> = HashMap::with_capacity(len);
+
+    let null_sentinel = match options.nulls_first {
+        true => 0_u8,
+        false => 0xFF,
+    };
+
+    let null_terminator = match options.descending {
+        true => 0xFF,
+        false => 0_u8,
+    };
+
+    let mut null_builder = BooleanBufferBuilder::new(len);
+    let mut keys = BufferBuilder::<K::Native>::new(len);
+    let mut values = Vec::with_capacity(len);
+    let mut null_count = 0;
+    let mut key_scratch = Vec::new();
+
+    for row in rows {
+        if row[0] == null_sentinel {
+            null_builder.append(false);
+            null_count += 1;
+            *row = &row[1..];
+            keys.append(K::Native::default());
+            continue;
+        }
+
+        let key_offset = row
+            .iter()
+            .skip(1)
+            .position(|x| *x == null_terminator)
+            .unwrap();
+        let key = &row[1..key_offset + 2];
+        *row = &row[key_offset + 2..];
+
+        let interned = match options.descending {
+            true => {
+                key_scratch.clear();
+                key_scratch.extend_from_slice(key);
+                key_scratch.iter_mut().for_each(|o| *o = !*o);
+                interner.lookup(&key_scratch).unwrap()
+            }
+            false => interner.lookup(key).unwrap(),
+        };
+
+        let k = *dictionary.entry(interned).or_insert_with(|| {
+            let k = values.len();
+            values.push(interner.value(interned));
+            K::Native::from_usize(k).unwrap()
+        });
+
+        keys.append(k);
+        null_builder.append(true);
+    }
+
+    let child = match &value_type {
+        DataType::Null => NullArray::new(values.len()).into_data(),
+        DataType::Boolean => decode_bool(&values),
+        DataType::Int8 => decode_primitive::<Int8Type>(&values),
+        DataType::Int16 => decode_primitive::<Int16Type>(&values),
+        DataType::Int32 => decode_primitive::<Int32Type>(&values),
+        DataType::Int64 => decode_primitive::<Int64Type>(&values),
+        DataType::UInt8 => decode_primitive::<UInt8Type>(&values),
+        DataType::UInt16 => decode_primitive::<UInt16Type>(&values),
+        DataType::UInt32 => decode_primitive::<UInt32Type>(&values),
+        DataType::UInt64 => decode_primitive::<UInt64Type>(&values),
+        DataType::Float16 => decode_primitive::<Float16Type>(&values),
+        DataType::Float32 => decode_primitive::<Float32Type>(&values),
+        DataType::Float64 => decode_primitive::<Float64Type>(&values),
+        DataType::Timestamp(TimeUnit::Second, _) => {
+            decode_primitive::<TimestampSecondType>(&values)
+        }
+        DataType::Timestamp(TimeUnit::Millisecond, _) => {
+            decode_primitive::<TimestampMillisecondType>(&values)
+        }
+        DataType::Timestamp(TimeUnit::Microsecond, _) => {
+            decode_primitive::<TimestampMicrosecondType>(&values)
+        }
+        DataType::Timestamp(TimeUnit::Nanosecond, _) => {
+            decode_primitive::<TimestampNanosecondType>(&values)
+        }
+        DataType::Date32 => decode_primitive::<Date32Type>(&values),
+        DataType::Date64 => decode_primitive::<Date64Type>(&values),
+        DataType::Time32(t) => match t {
+            TimeUnit::Second => decode_primitive::<Time32SecondType>(&values),
+            TimeUnit::Millisecond => decode_primitive::<Time32MillisecondType>(&values),
+            _ => unreachable!(),
+        },
+        DataType::Time64(t) => match t {
+            TimeUnit::Microsecond => decode_primitive::<Time64MicrosecondType>(&values),
+            TimeUnit::Nanosecond => decode_primitive::<Time64NanosecondType>(&values),
+            _ => unreachable!(),
+        },
+        DataType::Duration(TimeUnit::Second) => {
+            decode_primitive::<DurationSecondType>(&values)
+        }
+        DataType::Duration(TimeUnit::Millisecond) => {
+            decode_primitive::<DurationMillisecondType>(&values)
+        }
+        DataType::Duration(TimeUnit::Microsecond) => {
+            decode_primitive::<DurationMicrosecondType>(&values)
+        }
+        DataType::Duration(TimeUnit::Nanosecond) => {
+            decode_primitive::<DurationNanosecondType>(&values)
+        }
+        DataType::Interval(IntervalUnit::DayTime) => {
+            decode_primitive::<IntervalDayTimeType>(&values)
+        }
+        DataType::Interval(IntervalUnit::MonthDayNano) => {
+            decode_primitive::<IntervalMonthDayNanoType>(&values)
+        }
+        DataType::Interval(IntervalUnit::YearMonth) => {
+            decode_primitive::<IntervalYearMonthType>(&values)
+        }
+        DataType::Decimal128(p, s) => {
+            decode_decimal::<16, Decimal128Type>(&values, *p, *s)
+        }
+        DataType::Decimal256(p, s) => {
+            decode_decimal::<32, Decimal256Type>(&values, *p, *s)
+        }
+        DataType::Utf8 => decode_string::<i32>(&values),
+        DataType::LargeUtf8 => decode_string::<i64>(&values),
+        DataType::Binary => decode_binary::<i32>(&values),
+        DataType::LargeBinary => decode_binary::<i64>(&values),
+        _ => {
+            return Err(ArrowError::NotYetImplemented(format!(
+                "decoding dictionary values of {}",
+                value_type
+            )))
+        }
+    };
+
+    let data_type =
+        DataType::Dictionary(Box::new(K::DATA_TYPE), Box::new(value_type.clone()));
+
+    let builder = ArrayDataBuilder::new(data_type)
+        .len(len)
+        .null_bit_buffer(Some(null_builder.finish()))
+        .null_count(null_count)
+        .add_buffer(keys.finish())
+        .add_child_data(child);
+
+    Ok(DictionaryArray::from(builder.build_unchecked()))
+}
+
+/// Decodes a binary array from dictionary values
+///
+/// # Safety
+///
+/// Values must be valid UTF-8
+fn decode_binary<O: OffsetSizeTrait>(values: &[&[u8]]) -> ArrayData {
+    let capacity = values.iter().map(|x| x.len()).sum();

Review Comment:
   We aren't copying the values, but references to the values, but yes this potentially could be optimised



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