Convert an array into a Map - sql

Question

I have a table with a column like
[{"key":"e","value":["253","203","204"]},{"key":"st","value":["mi"]},{"key":"k2","value":["1","2"]}]
Which is of the format array<struct<key:string,value:array<string>>>
I want to convert the column into below format :
{"e":["253","203","204"],"st":["mi"],"k2":["1","2"]}
which is of the type map<string,array<string>>
I have tried exploding the array but that does not work. Any ideas how I can do this in hive.

Answer 1

Without use of external libraries it's impossible. Please refer to brickhouse or create your own UDAF.
Note: further code provides snippets to reproduce the problem and solving the problem that Hive's built-in functions can solve. i.e map<string,string> not map<string, array<string>>.
-- reproducing the problem
CREATE TABLE test_table(id INT, input ARRAY<STRUCT<key:STRING,value:ARRAY<STRING>>>);
INSERT INTO TABLE test_table
SELECT
1 AS id,
ARRAY(
named_struct("key","e", "value", ARRAY("253","203","204")),
named_struct("key","st", "value", ARRAY("mi")),
named_struct("key","k2", "value", ARRAY("1", "2"))
) AS input;
SELECT id, input FROM test_table;
+-----+-------------------------------------------------------------------------------------------------------+--+
| id | input |
+-----+-------------------------------------------------------------------------------------------------------+--+
| 1 | [{"key":"e","value":["253","203","204"]},{"key":"st","value":["mi"]},{"key":"k2","value":["1","2"]}] |
+-----+-------------------------------------------------------------------------------------------------------+--+
With exploding and using STRUCT features, we can split the keys and values.
SELECT id, exploded_input.key, exploded_input.value
FROM (
SELECT id, exploded_input
FROM test_table LATERAL VIEW explode(input) d AS exploded_input
) x;
+-----+------+----------------------+--+
| id | key | value |
+-----+------+----------------------+--+
| 1 | e | ["253","203","204"] |
| 1 | st | ["mi"] |
| 1 | k2 | ["1","2"] |
+-----+------+----------------------+--+
The idea is to use your UDAF to "collect" a map while aggregating on id.
What Hive can solve with built in function is generating map<string,string> by converting rows to strings with a special delimiter, aggregate rows via another special delimiter and use str_to_map built-in function on the delimiters to generate map<string, string>.
SELECT
id,
str_to_map(
-- outputs: e:253,203,204#st:mi#k2:1,2 with delimiters between aggregated rows
concat_ws('#', collect_list(list_to_string)),
'#', -- first delimiter
':' -- second delimiter
) mapped_output
FROM (
SELECT
id,
-- outputs 3 rows: (e:253,203,203), (st:mi), (k2:1,2)
CONCAT(exploded_input.key,':' , CONCAT_WS(',', exploded_input.value)) as list_to_string
FROM (
SELECT id, exploded_input
FROM test_table LATERAL VIEW explode(input) d AS exploded_input
) x
) y
GROUP BY id;
Which outputs a string to string map like:
+-----+-------------------------------------------+--+
| id | mapped_output |
+-----+-------------------------------------------+--+
| 1 | {"e":"253,203,204","st":"mi","k2":"1,2"} |
+-----+-------------------------------------------+--+

Answer 2

with input_set as (
select array(named_struct('key','e','value',array('253','203','204')),named_struct('key','st','value',array('mi')),named_struct('key','k2','value',array('1','2'))) as input_array
), break_input_set as (
select y.col_num as y_col_num,y.col_value as y_col_value from input_set lateral view posexplode(input_set.input_array) y as col_num, col_value
), create_map as (
select map(y_col_value.key,y_col_value.value) as final_map from break_input_set
)
select * from create_map;

Answer 3

var Array = [{"key":"e","value":["253","203","204"]},{"key":"st","value":["mi"]},{"key":"k2","value":["1","2"]}];
var obj = {}
for(var i=0;i<Array.length;i++){
obj[Array[i].key] = Array[i].value
}
obj will be in the required format