使用scala或pyspark读取hadoop中存储的Parquet文件时，出现错误：

# scala

var dff = spark.read.parquet("/super/important/df")
    org.apache.spark.sql.AnalysisException: Unable to infer schema for Parquet. It must be specified manually.;
      at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$8.apply(DataSource.scala:189)
      at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$8.apply(DataSource.scala:189)
      at scala.Option.getOrElse(Option.scala:121)
      at org.apache.spark.sql.execution.datasources.DataSource.org$apache$spark$sql$execution$datasources$DataSource$$getOrInferFileFormatSchema(DataSource.scala:188)
  at org.apache.spark.sql.execution.datasources.DataSource.resolveRelation(DataSource.scala:387)
  at org.apache.spark.sql.DataFrameReader.load(DataFrameReader.scala:152)
  at org.apache.spark.sql.DataFrameReader.parquet(DataFrameReader.scala:441)
  at org.apache.spark.sql.DataFrameReader.parquet(DataFrameReader.scala:425)
  ... 52 elided

或

sql_context.read.parquet(output_file)

导致相同的错误。
错误消息非常清楚必须做什么：无法推断Parquet地板的模式。必须手动指定。；。但我在哪能具体说明呢？
spark2.1.1、hadoop2.5、dataframes是在pyspark的帮助下创建的。文件被分成10个部分。