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Description
-----------

This algorithm returns the nexus (HDF) files in the given files list that satisfy the specified criteria.
This is done without actually loading the data, but just the needed metadata.
Input files need to exist and be specified following the Mantid rules in
:py:obj:`MultipleFileProperty <mantid.api.MultipleFileProperty>`.
Criteria could be any python logical expression involving the nexus entry names enclosed with ``$`` symbol.
Arbitrary number of criteria can be combined. The metadata entry should contain only one element.
Note, that if the entry is of string type, string comparison will be performed.
As a result, a string of the fully resolved file names satisfying the criteria
(and following the same algebra as in input, i.e. ``+`` or ``,``) will be returned.
Note, that this algorithm requires `h5py <https://pypi.python.org/pypi/h5py>`_ package installed.

**Example - Running SelectNexusFilesByMetadata**

.. code-block:: python

    res = SelectNexusFilesByMetadata(FileList='INTER00013460,13463,13464.nxs',
                                     NexusCriteria='$raw_data_1/duration$ > 1000 or $raw_data_1/good_frames$ > 10000')
    print("res is now a string containing comma separated paths of {} file names that satisfy the criteria".format(len(res.split(','))))

Output:

.. code-block:: none

   res is now a string containing comma separated paths of 2 file names that satisfy the criteria

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