Class FeatureDictWriter

object --+    
         |    
      dict --+
             |
            FeatureDictWriter

Utility class to encode data feature vectors (represented as string:value feature dictionaries) into a plain text file format.

These should then be re-read using the matching "FeatureDictReader" class. The basic strategy is to identify every feature encountered among the data items and assign each a unique index number. This class (which extends the dict class) stores the feature:index mappings and then prints out each data item with the corresponding index:value pairs.

>>> from cStringIO import StringIO
>>> from CHEM.ML.features.SpectrumExtractor import SpectrumExtractor
>>> dataList = ["asdfsdfg","asdfasdfASDF","dfghDFGH"]
>>> outfile = StringIO()
>>> kernel = SpectrumExtractor();
>>> kernel.k = 1;
>>> featureEnum = FeatureDictWriter(outfile)
>>> # Determine and output all of the feature:index mappings
>>> for item in dataList:
...     featureDict = kernel(item)
...     for feature in featureDict.iterkeys():
...         success = featureEnum.add(feature)
...
>>> # Output the feature dictionaries in index:value text format
>>> for item in dataList:
...     featureDict = kernel(item)
...     featureEnum.update( featureDict, item )
>>> print >> outfile, "<BLANKLINE>",            # Hack.  doctest doesn't like blank lines in expected output
>>> print outfile.getvalue().replace("\t"," "); # Doesn't like tabs either
# 0 a
# 1 s
# 2 d
# 3 g
# 4 f
# 5 A
# 6 F
# 7 S
# 8 D
# 9 h
# 10 G
# 11 H
asdfsdfg UNKNOWN_ID 0:1 1:2 2:2 3:1 4:2 
asdfasdfASDF UNKNOWN_ID 0:2 1:2 2:2 4:2 5:1 6:1 7:1 8:1 
dfghDFGH UNKNOWN_ID 2:1 3:1 4:1 6:1 8:1 9:1 10:1 11:1 
<BLANKLINE>