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MathGroup Archive 2007

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XML data structure parsing in Mathematica 6 using patterns

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81502] XML data structure parsing in Mathematica 6 using patterns
  • From: Daniel Flatin <dflatin at rcn.com>
  • Date: Wed, 26 Sep 2007 06:38:18 -0400 (EDT)

This is my third attempt at posting this message. Apologies if somehow
the first two got through. I saw no sign of them, however.

I have an XML data structure where I want to extract the start and end
times, for example:

timeBlock = XMLElement["time-layout", {"time-coordinate" -> "local",
  "summarization" -> "none"}, {XMLElement[
   "layout-key", {}, {"k-p12h-n14-1"}],
  XMLElement["start-valid-time", {}, {"2007-09-21T20:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-22T08:00:00-04:00"}],
  XMLElement["start-valid-time", {}, {"2007-09-22T08:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-22T20:00:00-04:00"}],
  XMLElement["start-valid-time", {}, {"2007-09-22T20:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-23T08:00:00-04:00"}],
  XMLElement["start-valid-time", {}, {"2007-09-23T08:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-23T20:00:00-04:00"}],
  XMLElement["start-valid-time", {}, {"2007-09-23T20:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-24T08:00:00-04:00"}],
  XMLElement["start-valid-time", {}, {"2007-09-24T08:00:00-04:00"}],
  XMLElement["end-valid-time", {}, {"2007-09-24T20:00:00-04:00"}]}]
 
I can do this by finding all start times and all end times and then
combining them, as in

getTimeSequence[timeBlock_] :=
 Module[{startBlock, endBlock, startT, endT},
  startBlock = Cases[timeBlock,
    XMLElement["start-valid-time", _, {startT_}] :> startT,
    Infinity];
  endBlock = Cases[timeBlock, XMLElement["end-valid-time", _, {endT_}]
:> endT,
    Infinity];
  Transpose[{startBlock, endBlock}]
  ]
 
Philosophically, I think I should be able to capture the start and end
times with a single pattern, but I can't make it work. For example I
have tried:

getTimeStartStopPairs[timeBlock_] :=
 Module[{startBlock, endBlock, startT, endT},
  Cases[
   timeBlock,
   PatternSequence[XMLElement["start-valid-time", _, {startT_}],
     XMLElement["end-valid-time", _, {endT_}]] :> {startT, endT},
   Infinity
   ]
  ]

Does anyone have any suggestions? I would like to learn how to do this
with just one pattern and I feel like I am misinterpreting how
PatternSequence works.

Thanks,
Dan


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