What fraction of our bridges are not reporting usage statistics?
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Usage:

1. Put metrics tarballs into a directory called in/.  The best parsing
   performance can be achieved by decompressing tarballs without
   extracting them.  The bridge-descriptors-* and consensuses-* tarballs
   are required for this analysis.

2. Clone metrics-lib.git, build descriptor.jar, and put it in this
   directory.

3. Download Apache Commons Codec and Compress and put the .jar files in
   this directory.

4. Parse descriptors and write all relevant parts to one file per bridge:
   $ javac
       -cp commons-codec-1.4.jar:commons-compress-1.3.jar:descriptor.jar
       ExtractDescriptorParts.java
   $ java
       -cp commons-codec-1.4.jar:commons-compress-1.3.jar:descriptor.jar:.
       ExtractDescriptorParts

5. Analyze descriptors parts bridge by bridge and determine whether it
   reported bridge stats at a given time, and if not, find out why not:
   $ javac AnalyzeDescriptorParts.java
   $ java AnalyzeDescriptorParts

6. Aggregate daily statistics that can be plotted:
   $ javac AggregateStats.java
   $ java AggregateStats

7. Plot results:
   $ R --slave -f plot.R

