Spark’s User Defined Functions in Java

In this article we will find the answer for questions: How to change the column in Spark? How to modify column in Spark? In other words: how to create a user defined function (UDF) and apply it.

For example, let’s have a look to UDF, that takes a String and returns a String.

For Spark < 2.3:

// for Spark < 2.3
UDF1<String, String> myUdf = param -> {
    String result = param + "hello_from_udf";
    return result;

Consider the function declaration: UDF1<String, String> partitionKey

The first String is the type of the param parameter. The second String is the return type of result.

For Spark >= 2.3:

// for Spark >= 2.3
UserDefinedFunction myUdf = udf(
        (String param) -> {
            String result = param + "hello_from_udf";
            return result;
        }, DataTypes.StringType

After we have declared and described the function, it needs to be registered:

sqlContext.udf().register("myUdfRegisteredName", myUdf, DataTypes.StringType);

Then it can be used by calling callUDF:

Dataset<?> df = sqlContext.parquetFile(taskSource);
df.withColumn("calculatedColumn", callUDF("myUdfRegisteredName", col("sourceColumn")))

Thus, we will apply myUdf to each value of the sourceColumn, and make the calculatedColumn from that values.

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