Setting and changing MetaInformation for arbitrary objects

Question

I work with a lot of dynamic data in {{date, datum}. . .} format,

datedatalist={{{2001, 1, 1}, 45.2}, {{2002, 1, 1}, 132.}, {{2003, 1, 2}, 121.1}};

and I have historically attached a header to each object in a format like

datedataObject={{header version, data series name, type (value, % change, etc.)}, datedatalist};

I can see advantages to using Mathematica's TemporalData[] type, and to using MetaInformation[] for recording the header. I would set this up with something like

newObject = TemporalData[datedatalist, MetaInformation -> {"name" -> "whatever", "type" -> "value"}];

and extract header items with, for example

newObject["name"]

But this leaves me with two puzzles,

1. How do I add MetaInformation after the object has been created? and
2. How do I change existing MetaInformation?

Answer 1

What about this?

Load your sample data

datedatalist={{{2001, 1, 1}, 45.2}, {{2002, 1, 1}, 132.}, {{2003, 1, 2}, 121.1}};
ct = TemporalData[datedatalist, MetaInformation -> {"name" -> "whatever", "type" -> "value"}];

Modify its meta information

ct=TemporalData[ct, MetaInformation->{"name"->"Johnny", "fat"->True}];
ct["MetaInformation"]
(* {"name" -> "Johnny", "fat" -> True, "type" -> "value"} *)

Answer 2

I sure hope there is a cleaner way to get both tasks than the following which is based on accessing and changing Parts of a temporal data object:

 s = Accumulate[
 RandomInteger[{-5, 1}, 10]~Join~RandomInteger[{-1, 5}, 10]]; 
 td = TemporalData[s, {1, 20}];
 td["Properties"]
(* {"Part","Path","PathComponents","PathCount","PathFunction",
   "PathFunctions","PathLengths","Paths","PathStates","PathTimes",
   "Properties","SliceData","SliceDistribution","StateDimensions",
    "States","Times"} *)

Add MetaInformation:

 td[[2, -1]] = AppendTo[td[[2, -1]], MetaInformation -> {"Event" -> 10}];
 td["Properties"]
 (* {"Event","Part","Path","PathComponents","PathCount","PathFunction",
    "PathFunctions","PathLengths","Paths","PathStates","PathTimes",
    "Properties","SliceData","SliceDistribution","StateDimensions",
    "States","Times"} *)

 td["Event"]
 (* 10 *)

Change the value of a MetaInformation element:

 d[[2, -1, 1, 2, 1, 2]] = 20;
 td["Event"]
 (* 20 *)

Add another MetaInformation element:

 td[[2, -1, 1, 2]] = AppendTo[td[[2, -1, 1, 2]], "name" -> "abc"];  
 td["MetaInformation"]
 (*{"Event" -> 20,"name" ->"abc"} *)
 td["name"]
 (* "abc" *)

Note: This approach works in version 9.0.1.0. Version 10 seems to have quite a few new features related to TemporalData. However, documentation information related to MetaInformation has not changed.

Answer 3

David Reiss came up with a nice kludge over in the Wolfram Communities --

newObject = newObject /. {("name" -> _) :> ("name" -> "Happy feet")}

changes the "name" part of the MetaInformation in newObject. And

newObject = 
 newObject /. {(MetaInformation -> x_) :> (MetaInformation -> Flatten[{x, "another" -> "Something"}])} 

adds the "another" -> "Something" rule to the MetaInformation of newObject.

This does seem like a bug in Mathematica though; the behavior is illogical and at odds with the documentation.