This post shows different methods of a DataFrame.
Get the first value in a column
df = some_dataframe_definition
value = df.select("SOME_COLUMN_NAME").first()[0]
Convert Dataframe to JSON
df = some_dataframe_definition result_json = df.toJSON()
Get a Row
df = some_dataframe_definition row = df.collect()[0] #You can switch out 0 for whatever row you want.
Count rows of Dataframe
df = some_dataframe_definition num_rows = df.count()