{"key": { "defaultWeights":"1" }, "measures": { "m1":-0.01, "m2":-0.5.....}}

val flattened = dff.withColumn("default_weights", json_tuple(col("key"), "defaultWeights")).show

org.apache.spark.sql.AnalysisException: cannot resolve 'json_tuple(`key`, 'defaultWeights')' due to data type mismatch: json_tuple requires that all arguments are strings;;
'Project [key#6, measures#7, json_tuple(key#6, defaultWeights) AS default_weights#13]
+- Relation[key#6,measures#7] json

<console>:25: error: type mismatch;
 found   : String
 required: org.apache.spark.sql.Column
       val flattened = dff.withColumn("default_weights", json_tuple("key", "defaultWeights")).show