Github user HyukjinKwon commented on a diff in the pull request: https://github.com/apache/spark/pull/21318#discussion_r187843889 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/functions.scala --- @@ -39,7 +39,21 @@ import org.apache.spark.util.Utils /** - * Functions available for DataFrame operations. + * Commonly used functions available for DataFrame operations. Using functions defined here provides + * a little bit more compile-time safety to make sure the function exists. + * + * Spark also includes more built-in functions that are less common and are not defined here. + * You can still access them (and all the functions defined here) using the [[functions.expr()]] API + * and calling them through a SQL expression string. You can find the entire list of functions for + * the latest version of Spark at [[https://spark.apache.org/docs/latest/api/sql/index.html]]. + * + * As an example, `isnan` is a function that is defined here. You can use `isnan(col("myCol"))` + * to invoke the isnan function. This way the programming language's compiler ensures isnan exists --- End diff -- nit: `isnan` -> `` `isnan` ``
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