def __init__(self, seq, overlapping=True, normalize=True):
self.seq = seq.upper()
self.overlapping = overlapping
self.normalize = normalize
# Sequence length
self.len = len(seq)
# Calculate dinuc. frequencies
self.du = DinucUsage(seq, Overlapping=overlapping)
if normalize:
self.du.normalize()
# Calculate frequencies for individual bases
A_base = "A"
T_base = "T"
U_base = "U"
G_base = "G"
C_base = "C"
self.bases = (A_base, T_base, G_base, C_base)
self.base_freqs = defaultdict(int)
for curr_base in self.bases:
self.base_freqs[curr_base] = \
(self.seq.count(curr_base) / float(self.len))
# Equalize T/U -- pick the greater of the two frequencies
# and then set them as equal
self.base_freqs[T_base] = max(
(self.base_freqs["T"], self.base_freqs["U"]))
self.base_freqs[U_base] = self.base_freqs[T_base]
def test_init_from_seq(self):
"""DinucUsage should init correctly from string."""
s1 = 'AAAAA'
s2 = 'ACTACG'
fd = filter_dict
self.assertEqual(fd(DinucUsage(s1)), {'AA': 4})
#NOTE: will map DNA seq tp RNA.
self.assertEqual(fd(DinucUsage(s2)), {
'AC': 2,
'CU': 1,
'UA': 1,
'CG': 1
})
#check that it works for non-overlapping
self.assertEqual(fd(DinucUsage(s1, Overlapping=False)), {'AA': 2})
self.assertEqual(fd(DinucUsage(s2, Overlapping=False)), \
{'AC':1,'UA':1,'CG':1})
#check that it works for the 3-1 case
self.assertEqual(fd(DinucUsage(s1, Overlapping='3-1')), {'AA': 1})
self.assertEqual(fd(DinucUsage(s2, Overlapping='3-1')), \
{'UA':1})
s3 = 'ACG' * 5
self.assertEqual(fd(DinucUsage(s3, Overlapping='3-1')), \
{'GA':4})
s4 = s3 + 'GAA'
self.assertEqual(fd(DinucUsage(s4, Overlapping='3-1')), \
{'GA':4,'GG':1})
def test_distance(self):
"""Dinuc distance should calculate Euclidean dist. correctly"""
s1 = 'AA' + 'GG' * 10
s2 = 'AA' * 5 + 'GG' * 7
d1 = DinucUsage(s1, Overlapping=False)
d2 = DinucUsage(s2, Overlapping=False)
self.assertEqual(d1.distance(d1), 0)
self.assertEqual(d1.distance(d2), 5)
self.assertEqual(d2.distance(d1), 5)
class DinucFreqs:
"""
Dinucleotide frequencies. Wrapper for pycogent class.
"""
def __init__(self, seq, overlapping=True, normalize=True):
self.seq = seq.upper()
self.overlapping = overlapping
self.normalize = normalize
# Sequence length
self.len = len(seq)
# Calculate dinuc. frequencies
self.du = DinucUsage(seq, Overlapping=overlapping)
if normalize:
self.du.normalize()
# Calculate frequencies for individual bases
A_base = "A"
T_base = "T"
U_base = "U"
G_base = "G"
C_base = "C"
self.bases = (A_base, T_base, G_base, C_base)
self.base_freqs = defaultdict(int)
for curr_base in self.bases:
self.base_freqs[curr_base] = \
(self.seq.count(curr_base) / float(self.len))
# Equalize T/U -- pick the greater of the two frequencies
# and then set them as equal
self.base_freqs[T_base] = max(
(self.base_freqs["T"], self.base_freqs["U"]))
self.base_freqs[U_base] = self.base_freqs[T_base]
def get_dinuc_freqs_from(self, base, all_bases="ATGC"):
"""
Get a list of dinucleotide base from the given base to
each other base.
base -> A
base -> T
...
"""
return [self.du["%s%s" %(base, possible_base)] \
for possible_base in all_bases]
def prob_score(self, subseq):
"""
Score probability of subseq in sequence.
"""
if len(subseq) == 0:
return 0
# Score first base
total_logscore = np.log(self.base_freqs[subseq[0]])
for prev_base, next_base in utils.iter_by_pair(subseq, 1):
# Score current dinucleotide
curr_dinuc = "%s%s" % (prev_base, next_base)
# Divide by sum of all other transitions from the previous base
curr_dinuc_freq = self.du[curr_dinuc]
denom_dinuc_freqs = np.sum(self.get_dinuc_freqs_from(prev_base))
total_logscore += (np.log(curr_dinuc_freq) - \
np.log(denom_dinuc_freqs))
total_score = np.exp(total_logscore)
return total_score
def get_expected_num(self, subseq):
"""
Calculcate the number of expected occurrences of subseq
based on dinucleotide frequencies.
"""
subseq_len = len(subseq)
# Calculcate score of sequence (its probability)
subseq_score = self.prob_score(subseq)
# Calculate the number of possible positions for the subseq
# to occur within the larger sequence
num_positions = self.len - subseq_len + 1
# Expected number is the score times the number of possible
# positions
exp_num = num_positions * subseq_score
return exp_num
def __str__(self):
return "DinucFreqs(len=%d, seq=%s)" % (self.len, self.seq)
def __repr__(self):
return self.__str__()
