Support writing signal procs with non-numeric mass values

- FillHistMappings will only fill a signal-style hist mapping (with
  the $MASS patter) when the mass property is convertible to a float. Fixes #1.
- WriteDatacards now uses more precision for writing process yields, just to be safe

CombineTools/interface/Utilities.h

@@ -5,6 +5,7 @@
 #include <map>
 #include <set>
 #include <string>
+#include <sstream>
 #include "boost/algorithm/string.hpp"
 #include "boost/lexical_cast.hpp"
 #include "boost/regex.hpp"
@@ -113,6 +114,9 @@ std::vector<std::vector<unsigned>> GenerateCombinations(
 
 std::vector<std::string> ParseFileLines(std::string const& file_name);
 
+
+bool is_float(std::string const& str);
+
 /**
  * Generate a vector of mass values using ranges and intervals specified in a
  * string

CombineTools/src/CombineHarvester_Datacards.cc

@@ -393,8 +393,22 @@ void CombineHarvester::FillHistMappings(std::vector<HistMapping> & mappings) {
     auto sig_proc_set =
         ch_signals.SetFromProcs(std::mem_fn(&ch::Process::process));
     for (auto sig_proc : sig_proc_set) {
-      mappings.emplace_back(sig_proc, bin, bin + "/" + sig_proc + "$MASS",
-                            bin + "/" + sig_proc + "$MASS_$SYSTEMATIC");
+      // should only add this mapping if the signal process has a numeric mass
+      // value, otherwise we will write it using the background rule above
+      auto masses = Set2Vec(ch_signals.cp()
+                                .process({sig_proc})
+                                .SetFromProcs(std::mem_fn(&ch::Process::mass)));
+      if (masses.size() != 1) {
+        throw std::runtime_error(FNERROR("Process " + sig_proc + " in bin " +
+                                         bin +
+                                         " has multiple entries with multiple "
+                                         "mass values, this is not supported"));
+
+      }
+      if (is_float(masses[0])) {
+        mappings.emplace_back(sig_proc, bin, bin + "/" + sig_proc + "$MASS",
+                              bin + "/" + sig_proc + "$MASS_$SYSTEMATIC");
+      }
     }
   }
 
@@ -662,7 +676,7 @@ void CombineHarvester::WriteDatacard(std::string const& name,
 
   txt_file << format("%-"+sys_str_long+"s") % "rate";
   for (auto const& proc : procs_) {
-    txt_file << format("%-15.4g ") % proc->no_norm_rate();
+    txt_file << format("%-15.8g ") % proc->no_norm_rate();
   }
   txt_file << "\n";
   txt_file << dashes << "\n";

CombineTools/src/Utilities.cc

@@ -237,6 +237,14 @@ std::vector<std::string> ParseFileLines(std::string const& file_name) {
   return files;
 }
 
+bool is_float(std::string const& str) {
+  std::istringstream iss(str);
+  float f;
+  iss >> std::noskipws >> f;  // noskipws considers leading whitespace invalid
+  // Check the entire string was consumed and if either failbit or badbit is set
+  return iss.eof() && !iss.fail();
+}
+
 std::vector<std::string> MassesFromRange(std::string const& input,
                                          std::string const& fmt) {
   std::set<double> mass_set;