[lmi] std::unordered_map vs std::map

[Greg Chicares]

Interestingly, I see virtually no performance difference in
  $make $coefficiency unit_tests unit_test_targets=ledger_test.exe |grep evalu  
  make_evaluator() : 1.572e-001 s mean;     150181 us least of   7 runs
if I
  %s/unordered_//g
as in the patch below. My measurements:
  150 ms std::map
  148 ms std::unordered_map
I don't plan to apply this patch, because there doesn't seem to be any
benefit, at least not with this compiler:
  $i686-w64-mingw32-g++ -dumpversion 
  7.3-win32

---------8<--------8<--------8<--------8<--------8<--------8<--------8<-------
diff --git a/ledger_evaluator.cpp b/ledger_evaluator.cpp
index 4213e918..b2b97458 100644
--- a/ledger_evaluator.cpp
+++ b/ledger_evaluator.cpp
@@ -51,7 +51,7 @@
 #include <functional>                   // minus
 #include <map>
 #include <numeric>                      // iota()
-#include <unordered_map>
+#include <map>
 #include <utility>                      // move(), pair
 
 namespace
@@ -75,9 +75,9 @@ std::vector<std::string> const suffixes
 
 // PDF !! Three maps, with similar but not necessarily identical
 // sets of keys, may not be the best imaginable data structure.
-typedef std::unordered_map<std::string, std::pair<int,oenum_format_style>> 
format_map_t;
-typedef std::unordered_map<std::string, std::string> title_map_t;
-typedef std::unordered_map<std::string, std::string> mask_map_t;
+typedef std::map<std::string, std::pair<int,oenum_format_style>> format_map_t;
+typedef std::map<std::string, std::string> title_map_t;
+typedef std::map<std::string, std::string> mask_map_t;
 
 // For all numbers (so-called 'scalars' and 'vectors', but not
 // 'strings') grabbed from all ledgers, look for a format. If one
@@ -859,8 +859,8 @@ ledger_evaluator Ledger::make_evaluator() const
 
     // Maps to hold the results of formatting numeric data.
 
-    std::unordered_map<std::string,std::string> stringscalars;
-    std::unordered_map<std::string,std::vector<std::string>> stringvectors;
+    std::map<std::string,std::string> stringscalars;
+    std::map<std::string,std::vector<std::string>> stringvectors;
 
     stringvectors["FundNames"] = invar.FundNames;
 
diff --git a/ledger_evaluator.hpp b/ledger_evaluator.hpp
index 1a2230bc..63cb05c2 100644
--- a/ledger_evaluator.hpp
+++ b/ledger_evaluator.hpp
@@ -29,7 +29,7 @@
 #include <boost/filesystem/path.hpp>
 
 #include <string>
-#include <unordered_map>
+#include <map>
 #include <vector>
 
 /// Class allowing to retrieve the string representation of any scalar or
@@ -39,7 +39,7 @@ class LMI_SO ledger_evaluator
 {
     friend class Ledger;
 
-    template<typename K, typename T> using umap = std::unordered_map<K,T>;
+    template<typename K, typename T> using umap = std::map<K,T>;
     using scalar_map_t = umap<std::string,            std::string >;
     using vector_map_t = umap<std::string,std::vector<std::string>>;
 
--------->8-------->8-------->8-------->8-------->8-------->8-------->8-------