10 <iota> [ 3 mod ] collect-by
] unit-test
+{
+ H{
+ { 0 V{ 0 3 6 9 0 3 6 9 } }
+ { 1 V{ 1 4 7 1 4 7 } }
+ { 2 V{ 2 5 8 2 5 8 } }
+ }
+} [
+ 10 <iota> [ 3 mod ] collect-by
+ 10 <iota> [ 3 mod ] collect-by!
+] unit-test
+
{ H{ { 1 4 } } } [ H{ { 1 2 } } 1 over [ sq ] ?change-at ] unit-test
{ H{ { 1 2 } } } [ H{ { 1 2 } } 2 over [ sq ] ?change-at ] unit-test
{ H{ { 1 3 } } } [ H{ { 1 2 } } 3 1 pick [ drop dup ] ?change-at drop ] unit-test