hdfmap

Map objects within an HDF5 or NeXus file and create a dataset namespace.

TL;DR - Usage

from hdfmap import create_nexus_map, load_hdf

# HdfMap from NeXus file - get dataset paths:
m = create_nexus_map('file.nxs')
m['energy']  # >> '/entry/instrument/monochromator/energy'
m['signal']  # >> '/entry/measurement/sum'
m['axes0']  # >> '/entry/measurement/theta'
m.get_image_path()  # >> '/entry/instrument/pil3_100k/data'

# load dataset data
with load_hdf('file.nxs') as nxs:
    path = m.get_path('scan_command')
    cmd = nxs[path][()]  # returns bytes data direct from file
    cmd = m.get_data(nxs, 'scan_command')  # returns converted str output
    cmd = m.eval(nxs, 'scan_command.strip()')  # returns evaluated output
    string = m.format_hdf(nxs, "the energy is {energy:.2f} keV")
    d = m.get_dataholder(nxs)  # classic data table, d.scannable, d.metadata
    xlabel, ylabel = m.generate_ids('axes', 'signal')  # return path identifier of name

# new in V1.0.0 - evaluate name based expressions in the original file
m('signal / count_time') # >> numpy array

# Shortcuts - single file reloader class (provides direct access to data)
from hdfmap import NexusLoader

scan = NexusLoader('file.hdf')
[data1, data2] = scan.get_data(['dataset_name_1', 'dataset_name_2'])
data = scan.eval('dataset_name_1 * 100 + 2')
string = scan.format('my data is {dataset_name_1:.2f}')
roi_sum = scan.eval('d_IMAGE[..., 90:110, 200:240].sum(axis=(-1, -2))')

# Shortcuts - multifile load data (generate map from first file)
from hdfmap import hdf_data, hdf_eval, hdf_format, hdf_image

all_data = hdf_data([f'file{n}.nxs' for n in range(100)], 'dataset_name')
normalised_data = hdf_eval(filenames, 'total / Transmission / (rc / 300.)')
descriptions = hdf_format(filenames, 'Energy: {en:5.3f} keV')
image_stack = hdf_image(filenames, index=31)

Installation

Requires: Python >=3.10, Numpy, h5py, hdf5plugin, asteval

from conda-forge

conda install -c conda-forge hdfmap

from PyPI

python -m pip install hdfmap

from GitHub

python -m pip install --upgrade git+https://github.com/DiamondLightSource/hdfmap.git

Description

Another generic hdf reader but the idea here is to build up a namespace dict of {'name': 'path'} for every dataset, then group them in a hopefully useful way.

Objects within the HDF file are separated into Groups and Datasets. Each object has a defined path and name identifier, as well as other attributes

• path -> '/entry/measurement/data' -> the location of an object within the file
• name -> data -> a dataset expressed as a simple variable name

Paths are unique locations within the file but can be used to identify similar objects in other files Names may not be unique within a file and are generated from the path.

Names of different types of datasets are stored for arrays (size > 0) and values (size 0) Names for scannables relate to all arrays of a particular size. Names for metadata relate to a subset of all datasets based on specified rules. Names for image_data relate to a subset of arrays that relate to images. A combined list of names is provided where scannables > image_data > arrays > values

Default Names

Several names are reserved and will be populated for NeXus files using attributes:

HdfMap Behaviours

from hdfmap import create_nexus_map
map = create_nexus_map('file.nxs')

HdfMap Attributes

E.G.

map.groups = {'/hdf/group': ('class', 'name', {attrs}, [datasets])}
map.classes = {'class_name': ['/hdf/group1', '/hdf/group2']}
map.datasets = {'/hdf/group/dataset': ('name', size, shape, {attrs})}
map.arrays = {'name': '/hdf/group/dataset'}
map.values = {'name': '/hdf/group/dataset'}
map.scannables = {'name': '/hdf/group/dataset'}
map.image_data = {'name': '/hdf/group/dataset'}

HdfMap Methods

HdfMap File Methods

NeXus Files

Files using the NeXus Format can generate special NexusMap objects. These work in the same way as the general HdfMaps but contain additional special names in the namespace:

In addition, the map.scannables dict will be populated automatically by the names given in the "scan_fields" dataset or by datasets from the first NXdata group. The default image data will be taken from the first NXdetector dataset.

Examples

scan data & metadata

Separate datasets in a NeXus file into Diamond's classic scannables and metadata, similar to what was in the old '*.dat' files.

from hdfmap import create_nexus_map, load_hdf

# HdfMap from NeXus file:
hmap = create_nexus_map('file.nxs')
with load_hdf('file.nxs') as nxs:
    scannables = hmap.get_scannables_array(nxs)  # creates 2D numpy array
    labels = scannables.dtype.names
    metadata = hmap.get_metadata(nxs)  # {'name': value}
    d = hmap.get_dataholder(nxs)  # classic data table, d.scannable, d.metadata
d.theta == d['theta']  # scannable array 'theta'
d.metadata.scan_command == d.metadata['scan_command']  # single value 'scan_command'

# OR, use the shortcut:
from hdfmap import nexus_data_block

d = nexus_data_block('file.nxs')

# The data loader class removes the need to open the files:
from hdfmap import NexusLoader

scan = NexusLoader('file.nxs')
metadata = scan.get_metadata()
scannables = scan.get_scannables()

automatic default plot axes

If defined in the nexus file, 'axes' and 'signal' will be populated automatically

import matplotlib.pyplot as plt
from hdfmap import create_nexus_map, load_hdf

# HdfMap from NeXus file:
hmap = create_nexus_map('file.nxs')
with load_hdf('file.nxs') as nxs:
    axes = hmap.get_data(nxs, 'axes')
    signal = hmap.get_data(nxs, 'signal')
    title = hmap.format_hdf(nxs, "{entry_identifier}\n{scan_command}")
xlabel, ylabel = hmap.generate_ids('axes', 'signal')
# plot the data (e.g. using matplotlib)
plt.figure()
plt.plot(axes, signal)
plt.xlabel(xlabel)
plt.ylabel(ylabel)
plt.title(title)

# Or, using NexusLoader:
from hdfmap import NexusLoader

scan = NexusLoader('file.nxs')
axes, signal = scan('axes, signal')
axes_label, signal_label = scan('_axes, _signal')
title = scan.format("{entry_identifier}\n{scan_command}")

Automatic image data

Get images from the first detector in a NeXus file

from hdfmap import create_nexus_map, load_hdf

# HdfMap from NeXus file:
hmap = create_nexus_map('file.nxs')
image_location = hmap.get_image_path()  # returns the hdf path chosen for the default detector
with load_hdf('file.nxs') as nxs:
    middle_image = hmap.get_image(nxs)  # returns single image from index len(dataset)//2
    first_image = hmap.get_image(nxs, 0)  # returns single image from dataset[0, :, :]
    volume = hmap.get_image(nxs, ())  # returns whole volume as array
    roi = hmap.get_image(nxs, (0, slice(5, 10, 1), slice(5, 10, 1)))  # returns part of dataset

# Or, using NexusLoader:
from hdfmap import NexusLoader

scan = NexusLoader('file.nxs')
image = scan.get_image(index=0)  # using index as defined above

Multi-scan metadata string

Generate a metadata string from every file in a directory very quickly. The HdfMap is only created for the first file, the remaining files are treated as having identical structure.

from hdfmap import list_files, hdf_format

format_string = "#{entry_identifier}: {start_time} : E={incident_energy:.3f} keV : {scan_command}"
files = list_files('/directoy/path', extension='.nxs')
strings_list = hdf_format(files, format_string)
print('\n'.join(strings_list))

# other multi-file readers:
from hdfmap import hdf_data, hdf_image, hdf_eval

data_list = hdf_data(files, 'incident_energy')
image_list = hdf_image(files, index=0)
data_list = hdf_eval(files, 'signal / Transmission')

Metadata Evaluation

Functionality for namespace evaluation of the hdf file allows for a number of rules allowing easy extraction of formatted metadata. The Evaluation functions are:

• HdfMap.eval(hdfobj, 'name') -> value
• HdfMap.format_hdf(hdfobj, '{name}') -> string
• HdfMap('name') -> value
• HdfLoader('eval') -> value
• HdfLoader.eval('eval') -> value
• HdfLoader.format('{name}') -> string
• hdf_eval([files], 'name') -> list[values]
• hdf_format([files], '{name}') -> list[string]

eval vs format

Evaluation functions evaluate the expression as given, replacing names in the hdfmap namespace with their associated values, or using the rules below. The format functions allow the input of python f-strings, allowing precise formatting to be applied and returning a string.

Rules

The following patterns are allowed in any expression:

• 'filename': str, name of hdf_file
• 'filepath': str, full path of hdf_file
• '_name': str hdf path of name
• '__name': str internal name of name (e.g. for 'axes')
• 's_name': string representation of dataset (includes units if available)
• 'd_name': return dataset object. warning: this may result in the hdf file or external files not closing on completion
• 'name@attr': returns attribute of dataset name
• 'name?(default)': returns default if name doesn't exist
• '(name1|name2|name3)': returns the first available of the names
• '(name1|name2@(default))': returns the first available name or default

Examples

from hdfmap import create_nexus_map, load_hdf

# HdfMap from NeXus file:
hmap = create_nexus_map('file.nxs')
with load_hdf('file.nxs') as nxs:
    # mathematical array expressions (using Numpy functions)
    data = hmap.eval(nxs, 'int(max(total / Transmission / count_time))')
    # return the path of a name
    path = hmap.eval(nxs, '_axes')  # -> '/entry/measurement/h'
    # return the real name of a variable
    name = hmap.eval(nxs, '__axes')  # -> 'h'
    # return label, using dataset attributes
    label = hmap.eval(nxs, 's_ppy')  # example uses @decimals and @units
    # return dataset object of default detector data
    detector_dataset = hmap.eval(nxs, 'd_IMAGE') # -> h5py.Dataset object
    # region of interest creation using lazy loading of default detector image
    roi_sum = hmap.eval(nxs, 'd_IMAGE[..., 90:110, 200:240].sum(axis=(-1, -2))') # -> ndarray
    # return dataset attributes
    attr = hmap.eval(nxs, 'idgap@units')  # -> 'mm'
    # return first available dataset
    cmd = hmap.eval(nxs, '(cmd|title|scan_command)')  # -> 'scan hkl ...'
    # return first available or default value
    atten = hmap.eval(nxs, '(gains_atten|atten?(0))')  # -> 0
    # python expression using multiple parameters
    pol = hmap.eval(nxs, '"pol in" if abs(delta_offset) < 0.1 and abs(thp) > 20 else "pol out"')
    # formatted strings
    title = hmap.format_hdf(nxs, '{filename}: {scan_command}')
    hkl = hmap.format_hdf(nxs, '({np.mean(h):.3g},{np.mean(k):.3g},{np.mean(l):.3g})')

# Or, using NexusLoader:
from hdfmap import NexusLoader

scan = NexusLoader('file.nxs')
# normalised default-signal
print(scan('signal / count_time / Transmission / (rc / 300.)'))
# axes label
print(scan.format('{__axes} [{axes@units}]'))

# Or, for multiple-files:
from hdfmap import hdf_eval, hdf_format, list_files

files = [f"file{n}.nxs" for n in range(10)]

energy_values = hdf_eval(files, '(en|energy@(8))')
list_scans = hdf_format(files, '{filename}: ({np.mean(h):.3g},{np.mean(k):.3g},{np.mean(l):.3g}) : {scan_command})')
print('\n'.join(list_scans))

Utilities

hdfmap comes with a number of useful utility functions for working with HDF5 files and NeXus files.

Generate Tree Descriptions

Generate string descriptions of the file tree structure

from hdfmap import hdf_tree_string

print(hdf_tree_string('file.nxs'))

output

 --- tests/data/1040323.nxs --- 
/
    @file_name: b'/dls/i16/data/2024/mm34617-1/1040323.nxs'
entry
    @NX_class: b'NXentry'
    @default: b'measurement'
entry/definition                                              :  b'NXmx'                :  
entry/diamond_scan
    @NX_class: b'NXcollection'
entry/diamond_scan/duration                                   :  47728                  :  @target=b'/entry/diamond_scan/duration', @units=b'ms'
entry/diamond_scan/end_time                                   :  b'2024-02-27T16:26:25.937'   :  @target=b'/entry/diamond_scan/end_time'
...

Find dataset paths

Get the HDF path of a Group or Dataset in a file using an ordered set of keywords. For NeXus files, these keywords can include the NX_class or local_name attribute.

from hdfmap import hdf_find, hdf_find_first

# Find datasets in top-level NXdata groups
group_paths, dataset_paths = hdf_find('file.nxs', 'NXentry', 'NXdata')
# group_paths = ['/entry/measurement']
# dataset_paths = ['/entry/measurement/x', '/entry/measurement/total']

# Find first NXdetector data
path = hdf_find_first('file.nxs', 'NXinstrument', 'NXdetector', 'data')
# path = '/entry/instrument/pil3_100k/data'

Compare HDF files

Generate a comparison string comparing the tree structure and datasets between two files.

from hdfmap import hdf_compare

print(hdf_compare('file1.nxs', 'file2.nxs'))

List all datasets

Generate a list of dataset paths from a HDF file.

from hdfmap import hdf_dataset_list, load_hdf

dataset_paths = hdf_dataset_list('file.nxs', all_links=True)

with load_hdf('file.nxs') as hdf:
    for path in dataset_paths:
        print(f"{path}: {hdf[path].dtype}, {hdf[path].shape}")

Find linked files

Find any external links in the file and return the files these link to. File paths returned are given as they are stored in the external link and are usually relative to the current file.

import os 
from hdfmap import hdf_linked_files

original_file = '/dir/to/file.nxs'
original_path = os.path.basename(original_file)
linked_files = hdf_linked_files(original_file)
for file in linked_files:
    file_path = os.path.join(original_path, file)
    print(file_path)