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     new d04357f72 Create 050-collect-to-list.md
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commit d04357f7263eeed9d433a0f33374e81c4bfca639
Author: Charles S. Givre <cgi...@apache.org>
AuthorDate: Thu Mar 16 10:39:40 2023 -0400

    Create 050-collect-to-list.md
---
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 1 file changed, 48 insertions(+)

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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"] |
+    
+----------------------------------------------------------------------------------+

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