Add selectPairs for non-hash table

selectPairs(x, f) is the same as select(pairs x, f)

Doesn't support iterators (yet) since select is defined for them at top-level.

M2/Macaulay2/d/actors4.d

@@ -200,6 +200,8 @@ select(e:Expr):Expr := (
      else WrongNumArgs(2,5));
 setupfun("select", select).Protected = false; -- will be overloaded in m2/lists.m2 and m2/regex.m2
 
+-- # typical value: selectPairs, HashTable, Function, HashTable
+-- # typical value: selectPairs, ZZ, HashTable, Function, HashTable
 selectPairs(nval:int, obj:HashTable, f:Expr):Expr := (
     u := newHashTable(obj.Class,obj.parent);
     u.beingInitialized = true;
@@ -228,18 +230,18 @@ selectPairs(nval:int, obj:HashTable, f:Expr):Expr := (
 		    "expected predicate to yield true or false"));
 	    p = p.next));
     Expr(sethash(u,obj.Mutable)));
+-- TODO: support iterators
 selectPairs(e:Expr):Expr := (
     when e
     is a:Sequence do (
-	-- # typical value: selectPairs, HashTable, Function, HashTable
 	if length(a) == 2 then (
 	    when a.0
 	    is obj:HashTable do (
 		if obj.Mutable
 		then WrongArgImmutableHashTable(1)
 		else selectPairs(obj.numEntries, obj, a.1))
-	    else WrongArgHashTable(1))
-	-- # typical value: selectPairs, ZZ, HashTable, Function, HashTable
+	    -- # typical value: selectPairs, BasicList, Function, Sequence
+	    else select(pairs(a.0), a.1))
 	else if length(a) == 3 then (
 	    when a.0
 	    is n:ZZcell do (
@@ -250,7 +252,8 @@ selectPairs(e:Expr):Expr := (
 			if obj.Mutable
 			then WrongArgImmutableHashTable(2)
 			else selectPairs(toInt(n), obj, a.2))
-		    else WrongArgHashTable(2)))
+		    -- # typical value: selectPairs, ZZ, BasicList, Function, Sequence
+		    else select(a.0, pairs(a.1), a.2, nullE, nullE)))
 	    else WrongArgZZ(1))
 	else WrongNumArgs(2, 3))
     else WrongNumArgs(2, 3));

M2/Macaulay2/packages/Macaulay2Doc/functions/select-doc.m2

@@ -265,7 +265,9 @@ doc ///
 doc ///
   Key
     selectPairs
+    (selectPairs, BasicList, Function)
     (selectPairs, HashTable, Function)
+    (selectPairs, ZZ, BasicList, Function)
     (selectPairs, ZZ, HashTable, Function)
   Headline
     select a part of a hash table by pairs
@@ -274,10 +276,10 @@ doc ///
     selectPairs(n, x, f)
   Inputs
     n:ZZ
-    x:HashTable -- must be immutable
+    x:{HashTable, BasicList}
     f:Function
   Outputs
-    :HashTable
+    :{HashTable, Sequence}
       containing all (or @VAR "n"@, if it is given) key-value pairs
       (@VAR "k"@,@VAR "v"@) from @VAR "x"@ for which @CODE "f(k,v)"@ evaluates
       to true.
@@ -286,6 +288,14 @@ doc ///
       x = hashTable{(1, 2), (2, 4), (3, 6), (4, 8), (5, 10)}
       selectPairs(x, (k,v) -> odd(k + v))
       selectPairs(2, x, (k, v) -> odd(k + v))
+    Text
+      If @CODE "x"@ is not a hash table, then @M2CODE "select(pairs x, f)"@
+      (or @M2CODE "select(n, pairs x, f)"@) is called.
+    Example
+      selectPairs(toList(1..10), (i, x) -> even x)
+      selectPairs(3, toList(1..10), (i, x) -> even x)
+  Caveat
+    If @CODE "x"@ is a hash table, then it must be immutable.
   SeeAlso
     selectValues
     selectKeys

M2/Macaulay2/tests/normal/iterators.m2

@@ -59,3 +59,6 @@ assert Equation(toList applyPairs("foo", (i, c) -> (c, i + 1)),
 x = 0
 scanPairs("foo", (i, c) -> x += i + first ascii c)
 assert Equation(x, 0 + 102 + 1 + 111 + 2 + 111)
+assert Equation(selectPairs(1..10, (i, x) -> even x),
+    ((1, 2), (3, 4), (5, 6), (7, 8), (9, 10)))
+assert Equation(selectPairs(2, 1..10, (i, x) -> even x), ((1, 2), (3, 4)))