Pyteomics documentation v4.5dev2



Source code for pyteomics.tandem

tandem - X!Tandem output file reader


`X!Tandem <>`_  is an open-source proteomic search
engine with a very simple, sophisticated application programming interface
(API): it simply takes an XML file of instructions on its command line,
and outputs the results into an XML file, which has been specified in the input
XML file. The output format is described
`here (PDF) <>`_.

This module provides a minimalistic way to extract information from X!Tandem
output files. You can use the old functional interface (:py:func:`read`) or the
new object-oriented interface (:py:class:`TandemXML`) to iterate over entries in
`<group>` elements, i.e. identifications for a certain spectrum.

Data access

  :py:class:`TandemXML` - a class representing a single X!Tandem output file.
  Other data access functions use this class internally.

  :py:func:`read` - iterate through peptide-spectrum matches in an X!Tandem
  output file. Data from a single PSM are converted to a human-readable dict.

  :py:func:`chain` - read multiple files at once.

  :py:func:`chain.from_iterable` - read multiple files at once, using an
  iterable of files.

  :py:func:`DataFrame` - read X!Tandem output files into a :py:class:`pandas.DataFrame`.

Target-decoy approach

  :py:func:`filter` - iterate through peptide-spectrum matches in a chain of
  X!Tandem output files, yielding only top PSMs and keeping false discovery rate
  (FDR) at the desired level. The FDR is estimated using the target-decoy
  approach (TDA).

  :py:func:`filter.chain` - chain a series of filters applied independently to
  several files.

  :py:func:`filter.chain.from_iterable` - chain a series of filters applied
  independently to an iterable of files.

  :py:func:`filter_df` - filter X!Tandem output files and return a :py:class:`pandas.DataFrame`.

  :py:func:`is_decoy` - determine if a PSM is from the decoy database.

  :py:func:`fdr` - estimate the FDR in a data set using TDA.

  :py:func:`qvalues` - get an array of scores and local FDR values for a PSM
  set using the target-decoy approach.

Deprecated functions

  :py:func:`iterfind` - iterate over elements in an X!Tandem file.
  You can just call the corresponding method of the :py:class:`TandemXML`


This module requires :py:mod:`lxml` and :py:mod:`numpy`.


#   Copyright 2012 Anton Goloborodko, Lev Levitsky
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.

import operator
from . import xml, auxiliary as aux, _schema_defaults

[docs]class TandemXML(xml.XML): """Parser class for TandemXML files.""" file_format = "TandemXML" _root_element = "bioml" _default_schema = _schema_defaults._tandem_schema_defaults _default_iter_path = 'group[@type="model"]' _structures_to_flatten = {'domain'}
[docs] def __init__(self, *args, **kwargs): if 'recursive' not in kwargs: super(TandemXML, self).__init__(*args, recursive=True, **kwargs) else: super(TandemXML, self).__init__(*args, **kwargs)
__init__.__doc__ = xml.XML.__init__.__doc__ def _get_info_smart(self, element, **kw): info = self._get_info(element, **kw) # handy simplifications below if isinstance(info.get('note'), list) and len(info['note']) == 1 and set(info['note'][0]) == {'label', 'note'}: info['note'] = info['note'][0]['note'] if 'protein' in info and 'label' in info: del info['label'] if 'group' in info: for g in info['group']: label = g.pop('label') type_ = g.pop('type') info.setdefault(type_, {})[label] = g del info['group'] if 'trace' in info: for t in info['trace']: info[t.pop('type')] = t del info['trace'] if isinstance(info.get('values'), dict): info['values'] = info['values']['values'] if isinstance(info.get('attribute'), list): for a in info.pop('attribute'): info[a['type']] = float(a['attribute']) if 'support' in info: for d in info['support'].get('supporting data', {}).values(): for label in ['Xdata', 'Ydata']: d[label]['values'] = d[label]['values'].astype(int) del d[label]['label'] if 'fragment ion mass spectrum' in info['support']: fims = info['support']['fragment ion mass spectrum'] fims.update(fims.pop('tandem mass spectrum')) for label in ['Xdata', 'Ydata']: del info['support']['fragment ion mass spectrum'][label]['label'] if 'charge' in info: info['charge'] = int(info['charge']) if info.get('rt') == '': info['rt'] = None return info def _get_schema_info(self, read_schema): return self._default_schema def __next__(self): n = super(TandemXML, self).__next__() del n['type'] return n next = __next__
[docs]def read(source, iterative=True, **kwargs): """Parse `source` and iterate through peptide-spectrum matches. Parameters ---------- source : str or file A path to a target X!Tandem output file or the file object itself. iterative : bool, optional Defines whether iterative parsing should be used. It helps reduce memory usage at almost the same parsing speed. Default is :py:const:`True`. Returns ------- out : iterator An iterator over dicts with PSM properties. """ return TandemXML(source, read_schema=False, recursive=True, iterative=iterative)
[docs]def iterfind(source, path, **kwargs): """Parse `source` and yield info on elements with specified local name or by specified "XPath". .. note:: This function is provided for backward compatibility only. If you do multiple :py:func:`iterfind` calls on one file, you should create a :py:class:`TandemXML` object and use its :py:meth:`!iterfind` method. Parameters ---------- source : str or file File name or file-like object. path : str Element name or XPath-like expression. Only local names separated with slashes are accepted. An asterisk (`*`) means any element. You can specify a single condition in the end, such as: ``"/path/to/element[some_value>1.5]"`` Note: you can do much more powerful filtering using plain Python. The path can be absolute or "free". Please don't specify namespaces. recursive : bool, optional If :py:const:`False`, subelements will not be processed when extracting info from elements. Default is :py:const:`True`. iterative : bool, optional Specifies whether iterative XML parsing should be used. Iterative parsing significantly reduces memory usage and may be just a little slower. When `retrieve_refs` is :py:const:`True`, however, it is highly recommended to disable iterative parsing if possible. Default value is :py:const:`True`. Returns ------- out : iterator """ return TandemXML(source, **kwargs).iterfind(path, **kwargs)
# chain = aux._make_chain(read, 'read') chain = aux.ChainBase._make_chain(TandemXML) def _is_decoy_prefix(psm, prefix='DECOY_'): """Given a PSM dict, return :py:const:`True` if all protein names for the PSM start with `prefix`, and :py:const:`False` otherwise. Parameters ---------- psm : dict A dict, as yielded by :py:func:`read`. prefix : str, optional A prefix used to mark decoy proteins. Default is `'DECOY_'`. Returns ------- out : bool """ return all(prot['label'].startswith(prefix) for prot in psm['protein']) def _is_decoy_suffix(psm, suffix='_DECOY'): """Given a PSM dict, return :py:const:`True` if all protein names for the PSM end with `suffix`, and :py:const:`False` otherwise. Parameters ---------- psm : dict A dict, as yielded by :py:func:`read`. suffix : str, optional A suffix used to mark decoy proteins. Default is `'_DECOY'`. Returns ------- out : bool """ return all(prot['label'].endswith(suffix) for prot in psm['protein']) is_decoy = _is_decoy_prefix qvalues = aux._make_qvalues(chain, _is_decoy_prefix, _is_decoy_suffix, operator.itemgetter('expect')) filter = aux._make_filter(chain, _is_decoy_prefix, _is_decoy_suffix, operator.itemgetter('expect'), qvalues) fdr = aux._make_fdr(_is_decoy_prefix, _is_decoy_suffix) filter.chain = aux._make_chain(filter, 'filter', True)
[docs]def DataFrame(*args, **kwargs): """Read X!Tandem output files into a :py:class:`pandas.DataFrame`. Requires :py:mod:`pandas`. Parameters ---------- sep : str or None, optional Some values related to PSMs (such as protein information) are variable-length lists. If `sep` is a :py:class:`str`, they will be packed into single string using this delimiter. If `sep` is :py:const:`None`, they are kept as lists. Default is :py:const:`None`. pd_kwargs : dict, optional Keyword arguments passed to the :py:class:`pandas.DataFrame` constructor. *args Passed to :py:func:`chain`. **kwargs Passed to :py:func:`chain`. Returns ------- out : pandas.DataFrame """ import pandas as pd data = [] prot_keys = ['id', 'uid', 'label', 'expect'] pep_keys = ['id', 'pre', 'post', 'start', 'end'] sep = kwargs.pop('sep', None) pd_kwargs = kwargs.pop('pd_kwargs', {}) with chain(*args, **kwargs) as f: for item in f: info = {} for k, v in item.items(): if isinstance(v, (str, int, float)): info[k] = v protein = item['protein'][0] for key in prot_keys: vals = [prot.get(key) for prot in item['protein']] if sep is not None: vals = sep.join(str(val) if val is not None else '' for val in vals) info['protein_' + key] = vals for key in pep_keys: vals = [prot['peptide'].get(key) for prot in item['protein']] if sep is not None: vals = sep.join(str(val) if val is not None else '' for val in vals) info['peptide_' + key] = vals aa = protein['peptide'].pop('aa', []) info['modifications'] = ','.join('{0[modified]:.3f}@{0[type]}'.format(x) for x in aa) for k in prot_keys: protein.pop(k, None) for k in pep_keys: protein['peptide'].pop(k, None) info.update(protein['peptide']) info['scan'] = item['support']['fragment ion mass spectrum']['note'] data.append(info) return pd.DataFrame(data, **pd_kwargs)
[docs]def filter_df(*args, **kwargs): """Read X!Tandem output files or DataFrames and return a :py:class:`DataFrame` with filtered PSMs. Positional arguments can be X!Tandem output files or DataFrames. Requires :py:mod:`pandas`. Parameters ---------- key : str / iterable / callable, optional Default is 'expect'. is_decoy : str / iterable / callable, optional Default is to check if all strings in the "protein" column start with `'DECOY_'` *args Passed to :py:func:`auxiliary.filter` and/or :py:func:`DataFrame`. **kwargs Passed to :py:func:`auxiliary.filter` and/or :py:func:`DataFrame`. Returns ------- out : pandas.DataFrame """ import pandas as pd sep = kwargs.get('sep') kwargs.setdefault('key', 'expect') if all(isinstance(arg, pd.DataFrame) for arg in args): if len(args) > 1: df = pd.concat(args) else: df = args[0] else: read_kw = {k: kwargs.pop(k) for k in ['iterative', 'read_schema', 'sep', 'pd_kwargs'] if k in kwargs} df = DataFrame(*args, **read_kw) if 'is_decoy' not in kwargs: if sep is not None: if 'decoy_suffix' in kwargs: kwargs['is_decoy'] = df['protein_label'].str.split(sep).apply( lambda s: all(x.endtswith(kwargs['decoy_suffix']) for x in s)) else: kwargs['is_decoy'] = df['protein_label'].str.split(sep).apply( lambda s: all(x.startswith(kwargs.get('decoy_prefix', 'DECOY_')) for x in s)) else: if 'decoy_suffix' in kwargs: kwargs['is_decoy'] = df['protein_label'].apply( lambda s: all(x.endswith(kwargs['decoy_suffix']) for x in s)) else: kwargs['is_decoy'] = df['protein_label'].apply( lambda s: all(x.startswith(kwargs.get('decoy_prefix', 'DECOY_')) for x in s)) return aux.filter(df, **kwargs)