regexp_replace(string, pattern, replacement)

Query

presto:default> SELECT regexp_replace('1a 2b 3c 6f', '(\d+)([abc]) ', 'aa$2 ') 
as expression;

Result

 expression 
---------------- 
 aaa aab aac 6f 
 (1 row)

Replace the instance of the string matched for the expression with the pattern and replacement string aa.