def nextseq_trim_index(sequence, cutoff, base=33):
"""
Variant of the above quality trimming routine that works on NextSeq data.
With Illumina NextSeq, bases are encoded with two colors. 'No color' (a
dark cycle) usually means that a 'G' was sequenced, but that also occurs
when sequencing falls off the end of the fragment. The read then contains
a run of high-quality G bases in the end.
This routine works as the one above, but counts qualities belonging to 'G'
bases as being equal to cutoff - 1.
"""
bases = sequence.sequence
qualities = sequence.qualities
s = 0
max_qual = 0
max_i = len(qualities)
for i in reversed(xrange(max_i)):
q = qual2int(qualities[i], base)
if bases[i] == 'G':
q = cutoff - 1
s += cutoff - q
if s < 0:
break
if s > max_qual:
max_qual = s
max_i = i
return max_i
def nextseq_trim_index(sequence, cutoff, base=33):
"""Variant of the above quality trimming routine that works on NextSeq
data. With Illumina NextSeq, bases are encoded with two colors.
'No color' (a dark cycle) usually means that a 'G' was sequenced, but
that also occurs when sequencing falls off the end of the fragment. The
read then contains a run of high-quality G bases in the end.
This routine works as the one above, but counts qualities belonging to
'G' bases as being equal to cutoff - 1.
"""
bases = sequence.sequence
qualities = sequence.qualities
score = 0
max_qual = 0
max_i = len(qualities)
for idx in reversed(range(max_i)):
qual = qual2int(qualities[idx], base)
if bases[idx] == 'G':
qual = cutoff - 1
score += cutoff - qual
if score < 0:
break
if score > max_qual:
max_qual = score
max_i = idx
return max_i
def summarize(self):
"""Flatten into a table of N*K rows, where N is the sequence size and
K is the union of keys in the nested dicts, and the columns are counts
by nucleotide.
"""
keys1 = set()
keys2 = set()
for dict1 in self.dicts:
keys1.update(dict1.keys())
for dict2 in dict1.values():
keys2.update(dict2.keys())
keys1 = tuple(sorted(keys1))
keys2 = tuple(sorted(keys2))
if self.is_qualities:
columns = tuple(qual2int(k, self.quality_base) for k in keys2)
else:
columns = keys2
return dict(columns=columns,
columns2=keys1,
rows=ordered_dict(
(idx,
ordered_dict((key1,
tuple(dict_item[key1].get(key2, 0)
for key2 in keys2))
for key1 in keys1))
for idx, dict_item in enumerate(self.dicts, 1)))
def quality_trim_index(qualities, cutoff_front, cutoff_back, base=33):
"""Find the position at which to trim a low-quality end from a
nucleotide sequence.
Qualities are assumed to be ASCII-encoded as chr(qual + base).
The algorithm is the same as the one used by BWA within the function
'bwa_trim_read':
- Subtract the cutoff value from all qualities.
- Compute partial sums from all indices to the end of the sequence.
- Trim sequence at the index at which the sum is minimal.
"""
start = 0
stop = max_i = len(qualities)
# find trim position for 5' end
score = 0
max_qual = 0
for idx in range(max_i):
qual = qual2int(qualities[idx], base)
score += cutoff_front - (qual - base)
if score < 0:
break
if score > max_qual:
max_qual = score
start = idx + 1
# same for 3' end
max_qual = 0
score = 0
for idx in reversed(range(max_i)):
qual = qual2int(qualities[idx], base)
score += cutoff_back - (qual - base)
if score < 0:
break
if score > max_qual:
max_qual = score
stop = idx
if start >= stop:
start, stop = 0, 0
return (start, stop)
def summarize(self):
"""Flatten into a table with N rows (where N is the size of the
sequence) and the columns are counts by nucleotide.
Returns:
A tuple of (columns, [rows]), where each row is
(position, (base_counts...))
"""
keys = set()
for dict_item in self.dicts:
keys.update(dict_item.keys())
if self.is_qualities:
keys = tuple(sorted(keys))
columns = tuple(qual2int(k, self.quality_base) for k in keys)
else:
acgt = ('A', 'C', 'G', 'T')
n_val = ('N', )
columns = keys = acgt + tuple(keys - set(acgt + n_val)) + n_val
return dict(columns=columns,
rows=ordered_dict(
(idx, tuple(dict_item.get(key, 0) for key in keys))
for idx, dict_item in enumerate(self.dicts, 1)))
def quality_trim_index(qualities, cutoff, base=33):
"""
Find the position at which to trim a low-quality end from a nucleotide sequence.
Qualities are assumed to be ASCII-encoded as chr(qual + base).
The algorithm is the same as the one used by BWA within the function
'bwa_trim_read':
- Subtract the cutoff value from all qualities.
- Compute partial sums from all indices to the end of the sequence.
- Trim sequence at the index at which the sum is minimal.
"""
s = 0
max_qual = 0
max_i = len(qualities)
for i in reversed(range(max_i)):
q = qual2int(qualities[i], base)
s += cutoff - q
if s < 0:
break
if s > max_qual:
max_qual = s
max_i = i
return max_i
def quality_trim_index(qualities, cutoff, base=33):
"""
Find the position at which to trim a low-quality end from a nucleotide sequence.
Qualities are assumed to be ASCII-encoded as chr(qual + base).
The algorithm is the same as the one used by BWA within the function
'bwa_trim_read':
- Subtract the cutoff value from all qualities.
- Compute partial sums from all indices to the end of the sequence.
- Trim sequence at the index at which the sum is minimal.
"""
s = 0
max_qual = 0
max_i = len(qualities)
for i in reversed(range(max_i)):
q = qual2int(qualities[i], base)
s += cutoff - q
if s < 0:
break
if s > max_qual:
max_qual = s
max_i = i
return max_i
