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new d04357f72 Create 050-collect-to-list.md
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commit d04357f7263eeed9d433a0f33374e81c4bfca639
Author: Charles S. Givre <[email protected]>
AuthorDate: Thu Mar 16 10:39:40 2023 -0400
Create 050-collect-to-list.md
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+---
+title: "COLLECT_LIST"
+slug: "List Creation Functions"
+parent: "Nested Data Functions"
+---
+Drill has several functions which can create lists/arrays or maps from your
data.
+
+## COLLECT_LIST
+This function takes the values of an expression and converts them into a map
+
+### Syntax
+
+ COLLECT_LIST(<key> <expr>)
+
+Where <key> is a literal containing a map key and <exper> is an expression.
The function can contain many key/value pairs.
+
+### Example
+
+ apache drill> SELECT collect_list('n_nationkey', n_nationkey, 'n_name',
n_name) as newlist
+ FROM (SELECT * from cp.`tpch/nation.parquet` limit 2) group by 'a';
+
+-------------------------------------------------------------------------------+
+ | newlist
|
+
+-------------------------------------------------------------------------------+
+ |
[{"n_nationkey":0,"n_name":"ALGERIA"},{"n_nationkey":1,"n_name":"ARGENTINA"}] |
+
+-------------------------------------------------------------------------------+
+ 1 row selected (0.186 seconds)
+
+
+
+## COLLECT_TO_LIST_VARCHAR
+This function takes the values of an expression and converts it to a
list/array.
+
+### Syntax
+
+ COLLECT_TO_LIST_VARCHAR(*column*)
+
+Where *column* is a column that will be converted to a list (array).
+
+### Example
+The following query takes the `position_title` field and converts that field
into a Drill list. This function does not remove duplicates, so if you use
this on a column
+containing non-unique values, it will simply convert all those values into a
list.
+
+ apache drill> SELECT collect_to_list_varchar(position_title) FROM (SELECT
* FROM cp.`employee.json` LIMIT 5);
+
+----------------------------------------------------------------------------------+
+ | EXPR$0
|
+
+----------------------------------------------------------------------------------+
+ | ["President","VP Country Manager","VP Country Manager","VP Country
Manager","VP Information Systems"] |
+
+----------------------------------------------------------------------------------+
