The credit rating agencies assign ratings to bonds according to the credit-worthiness of the issuer, and the "Big Three" credit rating agencies use a similar (though not identical) tiered rating system. These have a clear, logical order - using the S&P tiers, AAA > AA+ > AA > AA- > A+ > ... > BBB > B > ... > C. Moody's uses a similar system, but names their tiers differently (Aaa > Aa1 > Aa2 > ... > Baa1 > ... > C).
Your task is to design a program which takes as input a list of strings representing bond rating tiers and output the same list, sorted in descending order from the highest tier (AAA/Aaa) to the lowest tier (C).
Input / Output
You may choose the format of the input (list, one per argument, CSV file). You may assume that every item in the input list is a valid rating string and that all rating strings in a list came from the same rating agency. Additionally, you may assume that none of the funky NA-style ratings such as "NR" or "WR" will be included - this is strictly from "Aaa/AAA" to "C". There may be duplicate ratings in the input list, and if found they should not be removed.
You may also choose the format of the output as is appropriate for your language, with the only restriction being that it should be outputting some standard text encoding like UTF-8 or ASCII.
Rules and scoring
This is code golf, so lowest byte count wins, standard loopholes disallowed. Please specify what the input and output format is.
Example program and test cases
The example Python program below can be used as a standard example of the correct sort order. The lists
SP are the orderings to use.
Moody = ['Aaa', 'Aa1', 'Aa2', 'Aa3', 'A1', 'A2', 'A3', 'Baa1', 'Baa2', 'Baa3', 'Ba1', 'Ba2', 'Ba3', 'B1', 'B2', 'B3', 'Caa', 'Ca', 'C'] SP = ['AAA', 'AA+', 'AA', 'AA-', 'A+', 'A', 'A-', 'BBB+', 'BBB', 'BBB-', 'BB+', 'BB', 'BB-', 'B+', 'B', 'B-', 'CCC', 'CC', 'C'] test_cases = [ (['Aa2', 'Aaa', 'Aa1'], ['Aaa', 'Aa1', 'Aa2']), (['AA', 'AA-', 'AA+'], ['AA+', 'AA', 'AA-']), (['Baa1', 'Ba1', 'A1', 'B1', 'Aaa', 'C', 'Caa', 'Aa1'], ['Aaa', 'Aa1', 'A1', 'Baa1', 'Ba1', 'B1', 'Caa', 'C']), (['BBB+', 'BB+', 'A+', 'B+', 'AAA', 'C', 'CCC', 'AA+'], ['AAA', 'AA+', 'A+', 'BBB+', 'BB+', 'B+', 'CCC', 'C']), (['B3', 'B1', 'B2'], ['B1', 'B2', 'B3']), (['B-', 'B+', 'B'], ['B+', 'B', 'B-']), (['B3', 'Caa', 'Aa1', 'Caa', 'Ca', 'B3'], ['Aa1', 'B3', 'B3', 'Caa', 'Caa', 'Ca']), (['B-', 'CCC', 'AA+', 'CCC', 'CC', 'B-'], ['AA+', 'B-', 'B-', 'CCC', 'CCC', 'CC']) ] mdy_sort = lambda x: Moody.index(x) sp_sort = lambda x: SP.index(x) for l_in, l_out in test_cases: sort_key = mdy_sort if set(l_in).issubset(set(Moody)) else sp_sort assert sorted(l_in, key=sort_key) == l_out
In case the python-style test case formatting is inconvenient, I've output it as space-delimited input strings (grouped in two-line pairs input followed by output):
Aa2 Aaa Aa1 Aaa Aa1 Aa2 AA AA- AA+ AA+ AA AA- Baa1 Ba1 A1 B1 Aaa C Caa Aa1 Aaa Aa1 A1 Baa1 Ba1 B1 Caa C BBB+ BB+ A+ B+ AAA C CCC AA+ AAA AA+ A+ BBB+ BB+ B+ CCC C B3 B1 B2 B1 B2 B3 B- B+ B B+ B B- B3 Caa Aa1 Caa Ca B3 Aa1 B3 B3 Caa Caa Ca B- CCC AA+ CCC CC B- AA+ B- B- CCC CCC CC
Note: I mention the "Big Three" but only specify Moody's and S&P here - the reason is that the third, Fitch, uses the same system as S&P when you don't take into account the NA-style ratings, so including Fitch would be redundant.