Read the schema of a Spark DataFrame.
sdf_schema(x)An object coercable to a Spark DataFrame (typically, a
tbl_spark).
An R list, with each list element describing the
name and type of a column.
The type column returned gives the string representation of the
underlying Spark type for that column; for example, a vector of numeric
values would be returned with the type "DoubleType". Please see the
Spark Scala API Documentation
for information on what types are available and exposed by Spark.