Read and write to CSV files
This article provides examples for reading and writing to CSV files with Azure Databricks using Python, Scala, R, and SQL.
Databricks recommends the read_files table-valued function for SQL users to read CSV files.
read_files is available in Databricks Runtime 13.1 and later.
You can also use a temporary view. If you use SQL to read CSV data directly without using temporary views or
read_files, the following limitations apply:
You can configure several options for CSV file data sources. See the following Apache Spark reference articles for supported read and write options.
When reading CSV files with a specified schema, it is possible that the data in the files does not match the schema. For example, a field containing name of the city will not parse as an integer. The consequences depend on the mode that the parser runs in:
PERMISSIVE(default): nulls are inserted for fields that could not be parsed correctly
DROPMALFORMED: drops lines that contain fields that could not be parsed
FAILFAST: aborts the reading if any malformed data is found
To set the mode, use the
diamonds_df = (spark.read .format("csv") .option("mode", "PERMISSIVE") .load("/databricks-datasets/Rdatasets/data-001/csv/ggplot2/diamonds.csv") )
PERMISSIVE mode it is possible to inspect the rows that could not be parsed correctly using one of the following methods:
- You can provide a custom path to the option
badRecordsPathto record corrupt records to a file.
- You can add the column
_corrupt_recordto the schema provided to the DataFrameReader to review corrupt records in the resultant DataFrame.
badRecordsPath option takes precedence over
_corrupt_record, meaning that malformed rows written to the provided path do not appear in the resultant DataFrame.
Default behavior for malformed records changes when using the rescued data column.
Find malformed rows notebook
This feature is supported in Databricks Runtime 8.3 (unsupported) and above.
When using the
PERMISSIVE mode, you can enable the rescued data column to capture any data that wasn’t parsed because one or more fields in a record have one of the following issues:
- Absent from the provided schema.
- Does not match the data type of the provided schema.
- Has a case mismatch with the field names in the provided schema.
The rescued data column is returned as a JSON document containing the columns that were rescued, and the source file path of the record. To remove the source file path from the rescued data column, you can set the SQL configuration
spark.conf.set("spark.databricks.sql.rescuedDataColumn.filePath.enabled", "false"). You can enable the rescued data column by setting the option
rescuedDataColumn to a column name when reading data, such as
The CSV parser supports three modes when parsing records:
FAILFAST. When used together with
rescuedDataColumn, data type mismatches do not cause records to be dropped in
DROPMALFORMED mode or throw an error in
FAILFAST mode. Only corrupt records—that is, incomplete or malformed CSV—are dropped or throw errors.
rescuedDataColumn is used in
PERMISSIVE mode, the following rules apply to corrupt records:
- The first row of the file (either a header row or a data row) sets the expected row length.
- A row with a different number of columns is considered incomplete.
- Data type mismatches are not considered corrupt records.
- Only incomplete and malformed CSV records are considered corrupt and recorded to the
SQL example: Read CSV file
The following SQL example reads a CSV file using
-- mode "FAILFAST" aborts file parsing with a RuntimeException if malformed lines are encountered SELECT * FROM read_files( 's3://<bucket>/<path>/<file>.csv', format => 'csv', header => true, mode => 'FAILFAST')
Scala, R, and Python examples: Read CSV file
The following notebook shows how to read a file, display sample data, and print the data schema using Scala, R, and Python. The examples in this section use the diamonds dataset. Specify the path to the dataset as well as any options that you would like.
Read CSV files notebook
When the schema of the CSV file is known, you can specify the desired schema to the CSV reader with the
Read CSV files with schema notebook
SQL example using
SELECT * FROM read_files( 's3://<bucket>/<path>/<file>.csv', format => 'csv', header => false, schema => 'id string, date date, event_time timestamp')
Example: Pitfalls of reading a subset of columns
The behavior of the CSV parser depends on the set of columns that are read. If the specified schema is incorrect, the results might differ considerably depending on the subset of columns that is accessed. The following notebook presents the most common pitfalls.