mdfDatastore

Datastore for collection of MDF files

Description

Use the MDF datastore object to access data from a collection of MDF files.

Creation

Syntax

mdfds = mdfDatastore(location)

mdfds = mdfDatastore(__,Name=Value,Name=Value,...)

Description

mdfds = mdfDatastore(location) creates an MDFDatastore based on an MDF file or a collection of files in the folder specified by location. All files in the folder with extensions .mdf, .dat, or .mf4 are included.

mdfds = mdfDatastore(__,Name=Value,Name=Value,...) specifies function options and properties of mdfds using optional name-value pairs.

Input Arguments

location — Location of MDF datastore files

string | character vector | cell array | DsFileSet object

Location of MDF datastore files, specified as a string, character vector, cell array, or object.

• DsFileSet object — You can specify a DsFileSet object. For more information, see matlab.io.datastore.DsFileSet.

• FileSet object — You can specify location as a FileSet object. Specifying the location as a FileSet object leads to a faster construction time for datastores compared to specifying a path or DsFileSet object. For more information, see matlab.io.datastore.FileSet.

• File path — You can specify a single file path as a character vector or string scalar. You can specify multiple file paths as a cell array of character vectors or a string array.

  The path can be relative or absolute, or a URL to a remote server. The location argument can contain the wildcard character *. If location specifies a folder, by default the datastore includes all files in that folder with the extensions .mdf, .dat, or .mf4. You can use the FileExtensions parameter to limit or expand this list.

  The location as a file path can take one of these forms.

  Data Location	Form
  Current folder or MATLAB® path	To access files in the current folder or MATLAB path, specify the name of the files or folder in location. Include the extension when specifying files. Example: ["myFile2.mf4","myFile3.mf4"] Example: "myDataFolder"
  Other folders	To access files in a folder other than the current folder, specify the full or relative path name in location. Example: "C:\myFolder\myFile*.mf4" Example: "\myDataFolder"
  Remote location	To access files in a remote location, location must contain the full path of the files or folder specified as a uniform resource locator (URL) of the form: scheme://path_to_location Based on the remote location, scheme can be one of the values in this table. Remote Location scheme Amazon S3™ s3 Windows Azure® Blob Storage wasb, wasbs HDFS™ hdfs For more information, see Work with Remote Data. Example: "s3://bucketname/path_to_file/myMdfData/"

Data Types: string | char | cell | DsFileSet

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

These pairs set file information or object Properties. Allowed options are IncludeSubfolders, FileExtensions, and the properties ReadRaw, ReadSize, SelectedChannelGroupNumber, and SelectedChannelNames.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: SelectedChannelNames="Counter_B4"

IncludeSubfolders — Include files in subfolders

false (default) | true

Include files in subfolders, specified as a logical. Specify true to include files in each folder and recursively in subfolders.

Example: IncludeSubfolders=true

Data Types: logical

FileExtensions — Custom extensions for filenames to include in MDF datastore

[".mdf",".dat",".mf4"] (default) | string | char | cell

Custom extensions for filenames to include in the MDF datastore, specified as a string, string array, character vector, or cell array of character vectors. By default, the supported extensions include .mdf, .dat, and .mf4. If your files have custom or nonstandard extensions, use this Name-Value setting to include files with those extensions.

Example: FileExtensions=[".myformat1",".myformat2"]

Data Types: char | cell

Properties

ChannelGroups — All channel groups present in first MDF file

table

This property is read-only.

All channel groups present in first MDF file, returned as a table of the same format returned by the mdfChannelGroupInfo function.

Data Types: table

Channels — All channels present in first MDF file

table

This property is read-only.

All channels present in first MDF file, returned as a table of the same format returned by the mdfChannelInfo function.

Those channels targeted for reading must have the same name and belong to the same channel group in each file of the MDF datastore.

Data Types: table

Files — Files included in datastore

char | string | cell

Files included in the datastore, specified as a character vector, string, or cell array.

Example: ["file1.mf4","file2.mf4"]

Data Types: char | string | cell

ReadRaw — Read raw data values

false (default) | true

Read raw data values, specified as true or false. If specified true, data are read as raw values. If specified false, data are read as physical values. The default value is false.

Example: ReadRaw=true

Data Types: logical

ReadSize — Size of data returned by read

"file" (default) | numeric | duration

Size of data returned by the read function, specified as "file", a numeric value, or a duration. A string value of "file" causes the entire file to be read; a numeric double value specifies the number of records to read; and a duration value specifies a time range to read.

If you later change the ReadSize property value type, the datastore resets.

Example: 50

Data Types: double | string | char | duration

SelectedChannelGroupNumber — Channel group to read

numeric scalar

Channel group to read, specified as a numeric scalar value.

Example: 1

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64

SelectedChannelNames — Names of channels to read

string | char | cell

Names of channels to read, specified as a string, string array, character vector, or cell array.

Those channels targeted for reading must have the same name and belong to the same channel group in each file of the MDF datastore. Unless specified otherwise, the default value is the channel names in channel group 1 sorted in alphabetical order.

Example: "Counter_B4"

Data Types: char | string | cell

Object Functions

read	Read data in MDF datastore
readall	Read all data in MDF datastore
preview	Subset of data from MDF datastore
reset	Reset MDF datastore to initial state
hasdata	Determine if data is available to read from MDF datastore
partition	Partition MDF datastore
numpartitions	Number of partitions for MDF datastore
combine (MATLAB)	Combine data from multiple datastores
transform (MATLAB)	Transform datastore
isPartitionable (MATLAB)	Determine whether datastore is partitionable
isShuffleable (MATLAB)	Determine whether datastore is shuffleable

Examples

Create an MDF Datastore

Create an MDF datastore from the sample file CANape.MF4, and read it into a timetable.

mdfds = mdfDatastore("C:\myMDFData\CANape.MF4");
while hasdata(mdfds)
    m = read(mdfds);
end

Version History

Introduced in R2017b

R2023b: Conversion Argument Pair Removed

Because of the new mdfRead workflow underlying the mdfDatastore functionality, the Conversion name-value pair argument is no longer supported. Code that uses this option generates an error. Instead, you can use the ReadRaw property and name-value argument.

Minor corresponding updates of data types and formats are also made to the ReadSize, Channels, ChannelGroups, and SelectedChannelNames properties.

R2023a: Support for Remote File URLs

You can directly access MDF file data stored at remote locations, including Amazon S3, Azure^® Blob Storage, and HDFS.