orc

Syntax

extractORCSchema(fileName)

Details

The method parses the structure of the dataset in the specified ORC file and returns a table with two columns: name and type, representing the column names and data types respectively.

Parameters

• fileName: A STRING scalar indicating the ORC file name.

Examples

orc::extractORCSchema("userdata1.orc")

Syntax

loadORC(fileName,[schema],[column],[rowStart],[rowNum])

Details

The method loads ORC file data into a DolphinDB in-memory table and returns it. For supported ORC data types and conversion rules, refer to Data Type Mappings below.

Parameters

• fileName: A STRING scalar indicating the name of the ORC file.
• schema: A table containing column names and data types. To change a column's data type, modify the data type in the schema table.
• column (optional): An INT vector indicating the indices of the columns to read. If not specified, all columns are read.
• rowStart (optional): An INT scalar indicating the starting row from which to read the ORC file. If not specified, reading starts from the beginning of the file.
• rowNum (optional): An INT scalar indicating the number of rows to read. If not specified, reading continues until the end of the file.

Examples

orc::loadORC("userdata1.orc")

Note: Column names starting with underscores are not supported. If the ORC file contains such column names, the system automatically adds the letter "Z" as a prefix.

Syntax

loadORCEx(dbHandle,tableName,[partitionColumns],fileName,[schema],[column],[rowStart],[rowNum],[transform])

Details

The method converts ORC file data into a DolphinDB DFS table, then returns a table object containing the distributed table's metadata. For supported ORC data types and conversion rules, refer to Data Type Mappings below.

Parameters

• dbHandle: The handle of database.
• tableName: The name of the table.
• partitionColumns: A STRING scalar or vector indicating the partitioning columns. For non-SEQ partitioned databases, specify the partitioning columns. In composite partitions, partitionColumns is a STRING vector.
• fileName: A STRING scalar indicating the name of the ORC file.
• schema: A table containing column names and data types. To change a column's data type, modify the data type in the schema table.
• column (optional): An INT vector indicating the indices of the columns to read. If not specified, all columns are read.
• rowStart (optional): An INT scalar indicating the starting row from which to read the ORC file. If not specified, reading starts from the beginning of the file.
• rowNum (optional): An INT scalar indicating the number of rows to read. If not specified, reading continues until the end of the file.
• transform (optional): A unary function that accepts a table as its parameter. If specified, the partitioned table is created first, and then data is loaded. The specified transform function is applied to the data from the file, and the result is saved to the database.

Examples

• Without specifying transform, data is directly imported into the database without processing.

db = database("dfs://db1", RANGE, 0 500 1000)
orc::loadORCEx(db,`tb,`id,"userdata1.orc")

• Specifying transform to convert numerically represented dates and times (e.g., 20200101) to specific temporal types.

dbPath="dfs://db2"
db=database(dbPath,VALUE,2020.01.01..2020.01.30)
dataFilePath="userdata1.orc"
schemaTB=orc::extractORCSchema(dataFilePath)
update schemaTB set type="DATE" where name="date"
tb=table(1:0,schemaTB.name,schemaTB.type)
tb1=db.createPartitionedTable(tb,`tb1,`date);
def i2d(mutable t){
    return t.replaceColumn!(`date,datetimeParse(t.date),"yyyy.MM.dd"))
}
t = orc::loadORCEx(db,`tb1,`date,dataFilePath,datasetName,,,,i2d)

Syntax

orcDS(fileName,chunkSize,[schema],[skipRows])

Details

The method creates a vector of data sources based on the input file name. The number of sources is determined by the number of rows in the file and the chunkSize.

Parameters

• fileName: A STRING scalar indicating the ORC file name.
• chunkSize: An INT scalar indicating the number of rows each data source contains.
• schema: A table containing column names and data types. To change the data type of a column automatically determined by the system, modify the data type in the schema table and pass it the loadORC function as an argument.
• skipRows: An INT scalar indicating the number of rows to skip from the beginning of the file. The default value is 0.

Examples

>ds = orc::orcDS("userdata1.orc", 1000)
>size ds;
1
>ds[0];
DataSource<loadORC("userdata1.orc", , 0, 1000) >

Syntax

saveORC(table, fileName)

Details

The method saves a DolphinDB in-memory table as an ORC format file. Note that saving table data to an existing ORC file will overwrite the original content of the ORC file.

Parameters

• table: The in-memory table object to be saved.
• fileName: A STRING scalar indicating the name of the ORC file to save to.

Examples

orc::saveORC(tb, "example.orc")