Editing NWB files

This tutorial demonstrates how to edit NWB files in-place to make small changes to existing containers. To add or remove containers from an NWB file, see Adding/Removing Containers from an NWB File. How and whether it is possible to edit an NWB file depends on the storage backend and the type of edit.

Warning

Manually editing an existing NWB file can make the file invalid if you are not careful. We highly recommend making a copy before editing and running a validation check on the file after editing it. See Validating NWB files.

Editing datasets

When reading an HDF5 NWB file, PyNWB exposes h5py.Dataset objects, which can be edited in place. For this to work, you must open the file in read/write mode ("r+" or "a").

First, let’s create an NWB file with data:

from pynwb import NWBHDF5IO, NWBFile, TimeSeries
from datetime import datetime
from dateutil.tz import tzlocal
import numpy as np

nwbfile = NWBFile(
    session_description="my first synthetic recording",
    identifier="EXAMPLE_ID",
    session_start_time=datetime.now(tzlocal()),
    session_id="LONELYMTN",
)

nwbfile.add_acquisition(
    TimeSeries(
        name="synthetic_timeseries",
        description="Random values",
        data=np.random.randn(100, 100),
        unit="m",
        rate=10e3,
    )
)

with NWBHDF5IO("test_edit.nwb", "w") as io:
    io.write(nwbfile)

Now, let’s edit the values of the dataset

with NWBHDF5IO("test_edit.nwb", "r+") as io:
    nwbfile = io.read()
    nwbfile.acquisition["synthetic_timeseries"].data[:10] = 0.0

You can edit the attributes of that dataset through the attrs attribute:

with NWBHDF5IO("test_edit.nwb", "r+") as io:
    nwbfile = io.read()
    nwbfile.acquisition["synthetic_timeseries"].data.attrs["unit"] = "volts"

Changing the shape of dataset

Whether it is possible to change the shape of a dataset depends on how the dataset was created. If the dataset was created with a flexible shape, then it is possible to change in-place. Creating a dataset with a flexible shape is done by specifying the maxshape argument of the H5DataIO class constructor. Using a None value for a component of the maxshape tuple allows the size of the corresponding dimension to grow, such that is can be be reset arbitrarily long in that dimension. Chunking is required for datasets with flexible shapes. Setting maxshape, hence, automatically sets chunking to True, if not specified.

First, let’s create an NWB file with a dataset with a flexible shape:

from hdmf.backends.hdf5.h5_utils import H5DataIO

nwbfile = NWBFile(
    session_description="my first synthetic recording",
    identifier="EXAMPLE_ID",
    session_start_time=datetime.now(tzlocal()),
    session_id="LONELYMTN",
)

data_io = H5DataIO(data=np.random.randn(100, 100), maxshape=(None, 100))

nwbfile.add_acquisition(
    TimeSeries(
        name="synthetic_timeseries",
        description="Random values",
        data=data_io,
        unit="m",
        rate=10e3,
    )
)

with NWBHDF5IO("test_edit2.nwb", "w") as io:
    io.write(nwbfile)

The None``value  in the first component of ``maxshape means that the the first dimension of the dataset is unlimited. By setting the second dimension of maxshape to 100, that dimension is fixed to be no larger than 100. If you do not specify a``maxshape``, then the shape of the dataset will be fixed to the shape that the dataset was created with. Here, you can change the shape of the first dimension of this dataset.

with NWBHDF5IO("test_edit2.nwb", "r+") as io:
    nwbfile = io.read()
    nwbfile.acquisition["synthetic_timeseries"].data.resize((200, 100))

This will change the shape of the dataset in-place. If you try to change the shape of a dataset with a fixed shape, you will get an error.

Note

There are several types of dataset edits that cannot be done in-place: changing the shape of a dataset with a fixed shape, or changing the datatype, compression, chunking, max-shape, or fill-value of a dataset. For any of these, we recommend using the pynwb.NWBHDF5IO.export method to export the data to a new file. See Adding/Removing Containers from an NWB File for more information.

Editing groups

Editing of groups is not yet supported in PyNWB. To edit the attributes of a group, open the file and edit it using h5py:

import h5py

with h5py.File("test_edit.nwb", "r+") as f:
    f["acquisition"]["synthetic_timeseries"].attrs["description"] = "Random values in volts"

Warning

Be careful not to edit values that will bring the file out of compliance with the NWB specification.

Renaming groups and datasets

Rename groups and datasets in-place using the move method. For example, to rename the "synthetic_timeseries" group:

with h5py.File("test_edit.nwb", "r+") as f:
    f["acquisition"].move("synthetic_timeseries", "synthetic_timeseries_renamed")

You can use this same technique to move a group or dataset to a different location in the file. For example, to move the "synthetic_timeseries_renamed" group to the "analysis" group:

with h5py.File("test_edit.nwb", "r+") as f:
    f["acquisition"].move(
        "synthetic_timeseries_renamed",
        "/analysis/synthetic_timeseries_renamed",
    )