libtsxx [FEATURE]: provide filters lof and rsf

These filters effectively load a filter operator (be it IIR or FIR) with the
value of the first sample. This is done by first removing the value of the
first sample from the entire time series and by restoring this value after
application of the filter.

src/libs/libtsxx/filter.cc

@@ -399,6 +399,36 @@ namespace ts {
 
     /*----------------------------------------------------------------------*/
 
+    /*! remove first
+     */
+    Ttimeseries RemoveFirst::operator()(const Ttimeseries& s,
+                                        const bool& debug) const
+      { 
+        Tindex f=s.f();
+        RemoveFirst::Mf=s(f);
+        std::cout << "DBUG: remove " << RemoveFirst::Mf << std::endl;
+        s -= RemoveFirst::Mf;
+        return s; 
+      }
+
+    //! definition of static member data is required
+    double RemoveFirst::Mf=0;
+
+    /*----------------------------------------------------------------------*/
+
+    /*! restore first
+     */
+    Ttimeseries RestoreFirst::operator()(const Ttimeseries& s,
+                                         const bool& debug) const
+      { 
+        std::cout << "DBUG: restore " << RemoveFirst::Mf << std::endl;
+        s += RemoveFirst::Mf;
+        RemoveFirst::Mf=0.;
+        return s; 
+      }
+
+    /*----------------------------------------------------------------------*/
+
     //! function to generate filter class
     Tfilterhandle make_filter(std::string s,
                               const bool& debug)
@@ -456,6 +486,10 @@ namespace ts {
       } else if (ID=="nrm") {
         is >> v;
         fh=Tfh(new Normalize(v));
+      } else if (ID=="lof") {
+        fh=Tfh(new RemoveFirst());
+      } else if (ID=="rsf") {
+        fh=Tfh(new RestoreFirst());
       } else {
         TSXX_debug(debug, "make_filter", "  filter ID " + ID + " is unknown" );
         TSXX_UnknownFilterAbort("ts::filter::make_filter", ID.c_str());

src/libs/libtsxx/filter.h

@@ -324,6 +324,43 @@ namespace ts {
 
     /*----------------------------------------------------------------------*/
 
+    /*! \brief remove value of first sample from series
+     *
+     * \ingroup filter
+     *
+     * Subtract the value of the first sample from the entire series and store
+     * this value for later reference. This is useful to effectively load
+     * filters operators with the value of the first sample.
+     */
+    class RemoveFirst: public ts::filter::BasicFilter {
+      friend class RestoreFirst;
+      public:
+        RemoveFirst() { RemoveFirst::Mf=0.; }
+        Ttimeseries operator()(const Ttimeseries& s,
+                               const bool& debug=false) const;
+      private:
+        static double Mf;
+    }; // class RemoveFirst
+
+    /*----------------------------------------------------------------------*/
+
+    /*! \brief restore value of first sample to series
+     *
+     * \ingroup filter
+     *
+     * The value of the first sample previously subtracted by RemoveFirst will
+     * now be restored again. The stored value of the first sample is reset to
+     * zero after the operation.
+     */
+    class RestoreFirst: public ts::filter::BasicFilter {
+      public:
+        RestoreFirst() { }
+        Ttimeseries operator()(const Ttimeseries& s,
+                               const bool& debug=false) const;
+    }; // class RestoreFirst
+
+    /*----------------------------------------------------------------------*/
+
     /*! create a filter
      * \ingroup filter
      */

src/libs/libtsxx/filter_usage_text.txt

@@ -32,5 +32,8 @@ cus        calculate cumulative sum
 iset n1,n2,v
            set samples n1-n2 to value v
 noi a      add Gaussian random noise of rms amplitude a
+lof        load filters effectively with value of first sample by subtracting
+           first sample from entire series
+rsf        restore first sample, if lof was used previously
 # 
 # ----- END OF filter_usage_text.txt -----