extend CID selection syntax with: "[metals]" and "[nonmetals]"

"[nonmetals]" is the same as "[!metals]", but they differs when combined
with other elements, for example, "[nonmetals,Fe]" includes Fe
but [!metals,Fe] doesn't.

docs/analysis.rst

@@ -575,6 +575,7 @@ Let us go through the individual filters first:
 * `//*/(ALA)` (or `(ALA)`) -- selects residues with a given name.
 * `//*//CB` (or `CB:*` or `CB[*]`) -- selects atoms with a given name.
 * `//*//[P]` (or just `[P]`) -- selects phosphorus atoms.
+* `[metals]`, `[nonmetals]` -- selects metal or non-metal atoms.
 * `//*//:B` (or `:B`) -- selects atoms with altloc B.
 * `//*//:` (or `:`) -- selects atoms without altloc.
 * `//*//;q<0.5` (or `;q<0.5`) -- selects atoms with occupancy below 0.5
@@ -590,6 +591,7 @@ The syntax supports also comma-separated lists and negations with `!`:
 * `(!ALA)` -- all residues but alanine,
 * `[C,N,O]` -- all C, N and O atoms,
 * `[!C,N,O]` -- all atoms except C, N and O,
+* `[metals,Si]` -- all metal and Si atoms,
 * `:,A` -- altloc either empty or A (which makes one conformation),
 * `/1/A,B/20-40/CA[C]:,A` -- multiple selection criteria, all of them
   must be fulfilled.

src/select.cpp

@@ -63,16 +63,28 @@ inline void parse_cid_elements(const std::string& cid, size_t pos,
   elements.resize((size_t)El::END, char(inverted));
   for (;;) {
     size_t sep = cid.find_first_of(",]", pos);
-    if (sep == pos || sep > pos + 2)
-      wrong_syntax(cid, 0, "in [...]");
-    char elem_str[2] = {cid[pos], sep > pos+1 ? cid[pos+1] : '\0'};
-    Element el = find_element(elem_str);
-    if (el == El::X && (alpha_up(elem_str[0]) != 'X' || elem_str[1] != '\0'))
-      wrong_syntax(cid, 0, " (invalid element in [...])");
-    elements[el.ordinal()] = char(!inverted);
-    pos = sep + 1;
+    if (sep == pos || sep > pos + 2) {
+      if (sep == pos + 6 && cid.compare(pos, 6, "metals", 6) == 0) {
+        for (size_t i = 0; i < elements.size(); ++i)
+          if (is_metal(static_cast<El>(i)))
+            elements[i] = char(!inverted);
+      } else if (sep == pos + 9 && cid.compare(pos, 9, "nonmetals", 9) == 0) {
+        for (size_t i = 0; i < elements.size(); ++i)
+          if (!is_metal(static_cast<El>(i)))
+            elements[i] = char(!inverted);
+      } else {
+        wrong_syntax(cid, 0, "in [...]");
+      }
+    } else {
+      char elem_str[2] = {cid[pos], sep > pos+1 ? cid[pos+1] : '\0'};
+      Element el = find_element(elem_str);
+      if (el == El::X && (alpha_up(elem_str[0]) != 'X' || elem_str[1] != '\0'))
+        wrong_syntax(cid, 0, " (invalid element in [...])");
+      elements[el.ordinal()] = char(!inverted);
+    }
     if (cid[sep] == ']')
       break;
+    pos = sep + 1;
   }
 }
 

tests/test_misc.py

@@ -54,6 +54,10 @@ def selstr(s):
         self.assertEqual(selstr('/1/C/-72(DA)'), '/1/C/-72.(DA)/')
         self.assertEqual(selstr('C/-72--30'), '//C/-72.--30./')
         self.assertEqual(selstr('C/-72-2'), '//C/-72.-2./')
+        self.assertEqual(selstr('[metals]'), selstr('[!nonmetals]'))
+        self.assertEqual(selstr('[!metals]'), selstr('[nonmetals]'))
+        self.assertTrue('[X,H,B' in selstr('[!metals,He]'))
+        self.assertTrue('[!X,H,B' in selstr('[metals,He]'))
 
 if __name__ == '__main__':
     unittest.main()