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"""
.. _tut_info_objects:
The :class:`Info <mne.Info>` data structure
==============================================
"""
from __future__ import print_function
import mne
import os.path as op
###############################################################################
# The :class:`Info <mne.Info>` data object is typically created
# when data is imported into MNE-Python and contains details such as:
#
# - date, subject information, and other recording details
# - the sampling rate
# - information about the data channels (name, type, position, etc.)
# - digitized points
# - sensor–head coordinate transformation matrices
#
# and so forth. See the :class:`the API reference <mne.Info>`
# for a complete list of all data fields. Once created, this object is passed
# around throughout the data analysis pipeline.
#
# It behaves as a nested Python dictionary:
# Read the info object from an example recording
info = mne.io.read_info(
op.join(mne.datasets.sample.data_path(), 'MEG', 'sample',
'sample_audvis_raw.fif'), verbose=False)
###############################################################################
# List all the fields in the info object
print('Keys in info dictionary:\n', info.keys())
###############################################################################
# Obtain the sampling rate of the data
print(info['sfreq'], 'Hz')
###############################################################################
# List all information about the first data channel
print(info['chs'][0])
###############################################################################
# .. _picking_channels:
#
# Obtaining subsets of channels
# -----------------------------
#
# There are a number of convenience functions to obtain channel indices, given
# an :class:`mne.Info` object.
###############################################################################
# Get channel indices by name
channel_indices = mne.pick_channels(info['ch_names'], ['MEG 0312', 'EEG 005'])
###############################################################################
# Get channel indices by regular expression
channel_indices = mne.pick_channels_regexp(info['ch_names'], 'MEG *')
###############################################################################
# Get channel indices by type
channel_indices = mne.pick_types(info, meg=True) # MEG only
channel_indices = mne.pick_types(info, eeg=True) # EEG only
###############################################################################
# MEG gradiometers and EEG channels
channel_indices = mne.pick_types(info, meg='grad', eeg=True)
###############################################################################
# Get a dictionary of channel indices, grouped by channel type
channel_indices_by_type = mne.io.pick.channel_indices_by_type(info)
print('The first three magnetometers:', channel_indices_by_type['mag'][:3])
###############################################################################
# Obtaining information about channels
# ------------------------------------
# Channel type of a specific channel
channel_type = mne.io.pick.channel_type(info, 75)
print('Channel #75 is of type:', channel_type)
###############################################################################
# Channel types of a collection of channels
meg_channels = mne.pick_types(info, meg=True)[:10]
channel_types = [mne.io.pick.channel_type(info, ch) for ch in meg_channels]
print('First 10 MEG channels are of type:\n', channel_types)
###############################################################################
# Dropping channels from an info structure
# ----------------------------------------
#
# It is possible to limit the info structure to only include a subset of
# channels with the :func:`mne.pick_info` function:
# Only keep EEG channels
eeg_indices = mne.pick_types(info, meg=False, eeg=True)
reduced_info = mne.pick_info(info, eeg_indices)
print(reduced_info)
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