+
+: intersect-keys-as ( assoc seq exemplar -- elts )
+ [ [ of ] with ] dip zip-with-as sift-values ; inline
+
+: intersect-keys ( assoc seq -- elts )
+ over intersect-keys-as ; inline
+
+: values-of ( assoc seq -- seq' )
+ [ of ] with map ; inline
+
+: counts ( seq elts -- counts )
+ [ histogram ] dip intersect-keys ;
+
+: histogram-diff ( hashtable1 hashtable2 -- hashtable3 )
+ [ neg swap pick at+ ] assoc-each
+ [ 0 > ] filter-values ;
+
+: collect-by-multi! ( ... assoc seq quot: ( ... obj -- ... new-keys ) -- ... assoc )
+ [ keep swap ] curry rot [
+ [ push-at-each ] curry compose each
+ ] keep ; inline
+
+: collect-by-multi ( ... seq quot: ( ... obj -- ... new-keys ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-by-multi! ; inline
+
+
+: collect-assoc-by! ( ... assoc input-assoc quot: ( ... key value -- ... key' value' ) -- ... assoc )
+ rot [ '[ @ swap _ push-at ] assoc-each ] keep ; inline
+
+: collect-assoc-by ( ... input-assoc quot: ( ... key value -- ... key value ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-assoc-by! ; inline
+
+: collect-key-by! ( ... assoc input-assoc quot: ( ... key value -- ... new-key ) -- ... assoc )
+ '[ _ keepd ] collect-assoc-by! ; inline
+
+: collect-key-by ( ... input-assoc quot: ( ... key value -- ... new-key ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-key-by! ; inline
+
+: collect-value-by! ( ... assoc input-assoc quot: ( ... key value -- ... new-key ) -- ... assoc )
+ '[ _ keep ] collect-assoc-by! ; inline
+
+: collect-value-by ( ... input-assoc quot: ( ... key value -- ... new-key ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-value-by! ; inline
+
+
+: collect-assoc-by-multi! ( ... assoc input-assoc quot: ( ... key value -- ... new-keys value' ) -- ... assoc )
+ rot [ '[ @ swap _ push-at-each ] assoc-each ] keep ; inline
+
+: collect-assoc-by-multi ( ... assoc quot: ( ... key value -- ... new-keys value' ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-assoc-by-multi! ; inline
+
+
+: collect-key-by-multi! ( ... assoc input-assoc quot: ( ... key value -- ... new-keys ) -- ... assoc )
+ '[ _ keepd ] collect-assoc-by-multi! ; inline
+
+: collect-key-by-multi ( ... assoc quot: ( ... key -- ... new-keys ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-key-by-multi! ; inline
+
+
+: collect-value-by-multi! ( ... assoc input-assoc quot: ( ... key value -- ... new-keys ) -- ... assoc )
+ '[ _ keep ] collect-assoc-by-multi! ; inline
+
+: collect-value-by-multi ( ... assoc quot: ( ... value -- ... new-keys ) -- ... assoc )
+ [ H{ } clone ] 2dip collect-value-by-multi! ; inline