making index with python

Question

the following is my question: data = ['a1_1 00000001\n', 'a1_2 00000002\n', 'a1_3 00000003\n', 'b1_1 00000004\n', 'b1_2 00000005\n', 'b1_3 00000006'] candidate = ['a', 'b'] for i in candidate: for j in data: if i in j.split()[0]: print i, j.split()[1] a 00000001 a 00000002 a 00000003 b 00000004 b 00000005 b 00000006 But what I want to do is to make the result like the following: a 00000001, 00000002, 00000003 b 00000004, 00000005, 00000006 How do I solve this problem? Thanks in advance! JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

data = ['a1_1 00000001\n', 'a1_2 00000002\n', 'a1_3 00000003\n', 'b1_1 00000004\n', 'b1_2 00000005\n', 'b1_3 00000006'] candidate = ['a', 'b'] for i in candidate: print i, ', '.join(v for k,v in (a.split() for a in data) if k.startswith(i)) prints: a 00000001, 00000002, 00000003 b 00000004, 00000005, 00000006 This will, however, go through data several times (once for each candidate). To do it once only, you will need an intermediary dictionary: d = {} for a in data: d.setdefault(a[0], []).append(a.split()[1]) for k,v in sorted(d.iteritems()): print k, ', '.join(v)