Convert rich types

src/column.js

@@ -1,7 +1,7 @@
-import { CompressionCodec, Encoding, PageType } from './constants.js'
+import { CompressionCodec, ConvertedType, Encoding, PageType } from './constants.js'
 import { assembleObjects, readDataPage, readDictionaryPage } from './datapage.js'
 import { parquetHeader } from './header.js'
-import { getMaxDefinitionLevel, isRequired } from './schema.js'
+import { getMaxDefinitionLevel, isRequired, schemaElement } from './schema.js'
 import { snappyUncompress } from './snappy.js'
 
 /**
@@ -11,6 +11,8 @@ import { snappyUncompress } from './snappy.js'
  * @typedef {import('./types.js').RowGroup} RowGroup
  */
 
+const dayMillis = 86400000000000 // 1 day in milliseconds
+
 /**
  * Read a column from the file.
  *
@@ -113,11 +115,16 @@ export function readColumn(arrayBuffer, rowGroup, columnMetadata, schema) {
       } else {
         if (dictionaryEncoding && dictionary !== undefined && Array.isArray(dataPage)) {
           // dereference dictionary values
+          values = []
           for (let i = 0; i < dataPage.length; i++) {
-            dataPage[i] = dictionary[dataPage[i]]
+            values[i] = dictionary[dataPage[i]]
           }
+        } else if (Array.isArray(dataPage)) {
+          // convert primitive types to rich types
+          values = convert(dataPage, schemaElement(schema, columnMetadata.path_in_schema))
+        } else {
+          values = dataPage // TODO: data page shouldn't be a fixed byte array?
         }
-        values = dataPage
       }
 
       // TODO: check that we are at the end of the page
@@ -155,3 +162,44 @@ export function getColumnOffset(columnMetadata) {
   }
   return Number(columnOffset)
 }
+
+/**
+ * Convert known types from primitive to rich.
+ *
+ * @param {any[]} data series of primitive types
+ * @param {SchemaElement} schemaElement schema element for the data
+ * @returns {any[]} series of rich types
+ */
+function convert(data, schemaElement) {
+  const ctype = schemaElement.converted_type
+  if (!ctype) return data
+  if (ctype === ConvertedType.UTF8) {
+    const decoder = new TextDecoder()
+    return data.map(v => decoder.decode(v))
+  }
+  if (ctype === ConvertedType.DECIMAL) {
+    const scaleFactor = Math.pow(10, schemaElement.scale || 0)
+    if (typeof data[0] === 'number') {
+      return data.map(v => v * scaleFactor)
+    } else {
+      // TODO: parse byte string
+      throw new Error('parquet decimal byte string not supported')
+    }
+  }
+  if (ctype === ConvertedType.DATE) {
+    return data.map(v => new Date(v * dayMillis))
+  }
+  if (ctype === ConvertedType.TIME_MILLIS) {
+    return data.map(v => new Date(v))
+  }
+  if (ctype === ConvertedType.JSON) {
+    return data.map(v => JSON.parse(v))
+  }
+  if (ctype === ConvertedType.BSON) {
+    throw new Error('parquet bson not supported')
+  }
+  if (ctype === ConvertedType.INTERVAL) {
+    throw new Error('parquet interval not supported')
+  }
+  return data
+}

src/constants.js

@@ -27,6 +27,31 @@ export const FieldRepetitionType = {
   REPEATED: 2,
 }
 
+export const ConvertedType = {
+  UTF8: 0,
+  MAP: 1,
+  MAP_KEY_VALUE: 2,
+  LIST: 3,
+  ENUM: 4,
+  DECIMAL: 5,
+  DATE: 6,
+  TIME_MILLIS: 7,
+  TIME_MICROS: 8,
+  TIMESTAMP_MILLIS: 9,
+  TIMESTAMP_MICROS: 10,
+  UINT_8: 11,
+  UINT_16: 12,
+  UINT_32: 13,
+  UINT_64: 14,
+  INT_8: 15,
+  INT_16: 16,
+  INT_32: 17,
+  INT_64: 18,
+  JSON: 19,
+  BSON: 20,
+  INTERVAL: 21,
+}
+
 export const CompressionCodec = {
   UNCOMPRESSED: 0,
   SNAPPY: 1,

src/types.d.ts

@@ -81,6 +81,17 @@ export enum ConvertedType {
   TIME_MICROS = 8,
   TIMESTAMP_MILLIS = 9,
   TIMESTAMP_MICROS = 10,
+  UINT_8 = 11,
+  UINT_16 = 12,
+  UINT_32 = 13,
+  UINT_64 = 14,
+  INT_8 = 15,
+  INT_16 = 16,
+  INT_32 = 17,
+  INT_64 = 18,
+  JSON = 19,
+  BSON = 20,
+  INTERVAL = 21,
 }
 
 export interface RowGroup {