Fixed getting empty selections.

test/system/datasettest.py

@@ -2,7 +2,7 @@ import unittest
 import sys
 sys.path.append('../..')
 from system.dataset import *
-from scipy import rand,shape
+from scipy import rand,shape, array
 
 class DatasetTest(unittest.TestCase):
     
@@ -37,9 +37,12 @@ class DatasetTest(unittest.TestCase):
         self.assertEquals(['gene_a', 'gene_b', 'gene_c'], data.get_identifiers('genes', [0, 1, 2]))
         # "advanced" lookup
         self.assertEquals(['gene_c', 'gene_a'], data.get_identifiers('genes', [2, 0]))
+        # handle empty matrix of indices
+        self.assertEquals([], data.get_identifiers('samples', array([])))
         # other dimension
         self.assertEquals(['sample_a', 'sample_b'], data.get_identifiers('samples', [0, 1]))
         
+        
     #def testExtraction(self):
     #    ids = ['gene_a','gene_b']
     #    dim_name = 'genes'