Load pandas dataframe into Spark cluster - postgresql

Question

I have a postgres database and I want to run a query and load a table into spark dataframe. some columns of my database are array. For example:
=> select id, f_2 from raw limit 1;
will return
id | f_2
---------+-----------
1 | {{140,130},{NULL,NULL},{NULL,NULL}}
what I want is accessing to 140 (first element of inner array) that is easy in postgres using this query:
=> select id, f_2[1][1] from raw limit 1;
id | f_2
---------+-----------
1 | 140
but I want to load it into spark dataframe and here is my code to load data:
df = sqlContext.sql("""
select id as id,
f_2 as A
from raw
""")
and return this error:
Py4JJavaError: An error occurred while calling o560.collectToPython.
: org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 4.0 failed 1 times, most recent failure: Lost task 0.0 in stage 4.0 (TID 4, localhost, executor driver): java.lang.ClassCastException: [Ljava.lang.Integer; cannot be cast to java.lang.Integer
and then I tried this one:
df = sqlContext.sql("""
select id as id,
f_2[0] as A
from raw
""")
and got same error and then tried this one:
df = sqlContext.sql("""
select id as id,
f_2[0][0] as A
from raw
""")
and return this error:
ERROR: An unexpected error occurred while tokenizing input
The following traceback may be corrupted or invalid
The error message is: ('EOF in multi-line string', (1, 0))
AnalysisException: u"Can't extract value from f_2#32685[0];"