Data update

Task/Digital-root/DuckDB/digital-root.duckdb

@@ -0,0 +1,26 @@
+# n is normally an integer but can be anything
+create or replace function sum_digits(n) as (
+  regexp_extract_all(n::VARCHAR, '.')
+    .list_transform( x -> (ascii(x) - 48) % 10)
+    .list_sum()
+);
+
+# n should be an integer
+create or replace function digital_root(n) as table (
+  with recursive cte as (
+    select 0 as ix, n as sum
+    union all
+    select ix+1, sum_digits(sum)
+    from cte
+    where length(sum::VARCHAR) > 1
+  )
+  select last(ix order by ix) as persistence,
+         last(sum order by ix) as "digital root",
+  from cte
+);
+
+## Examples:
+from (select unnest(range(0, 4)) as i,
+      unnest([627615, 39390, 588225, 393900588225]) as n),
+     (from digital_root(n))
+order by i;