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@ -1,7 +1,21 @@
# MatFileHandler
This document briefly describes how to perform simple operations with .mat files using MatFileHandler.
If you have questions and/or ideas, you can [file a new issue](https://github.com/mahalex/MatFileHandler/issues/new) or contact me directly at <mahalex@gmail.com>.
This document briefly describes how to perform simple operations with .mat files
using MatFileHandler.
If you have questions and/or ideas, you can [file a new issue]
(https://github.com/mahalex/MatFileHandler/issues/new) or contact me directly at
<mahalex@gmail.com>.
## Changelog
* Version `1.3.0` adds (read-only) support for Matlab objects, as well as an
interface to read tables.
* Version `1.2.0` makes data compression when writing files optional.
* Version `1.1.0` adds multi-targeting: the project now targets .NET Framework
4.6.1 as well as .NET Standard 2.0.
## Reading a .mat file
@ -24,9 +38,11 @@ foreach (IVariable variable in matFile.Variables) {
// Do stuff
}
```
(all of the interfaces and classes described in this text are in the `MatFileHandler` namespace).
(all of the interfaces and classes described in this text are in the
`MatFileHandler` namespace).
Each `IVariable` has a name, a value, and a flag indicating if it's a “global” variable:
Each `IVariable` has a name, a value, and a flag indicating if it's a “global”
variable:
```csharp
public interface IVariable
{
@ -36,8 +52,12 @@ public interface IVariable
}
```
The interesting part here is the `IArray` interface. This is a base interface, which is extended by other interfaces that provide access to more specific MATLAB arrays (numerical, cell, structure, char, etc.).
We can't do much with `IArray` itself: check for emptiness, get its dimensions and total number of elements in it, or try to convert it to an array of double (or complex) numbers:
The interesting part here is the `IArray` interface. This is a base interface,
which is extended by other interfaces that provide access to more specific
MATLAB arrays (numerical, cell, structure, char, etc.).
We can't do much with `IArray` itself: check for emptiness, get its dimensions
and total number of elements in it, or try to convert it to an array of double
(or complex) numbers:
```csharp
public interface IArray
{
@ -49,11 +69,22 @@ public interface IArray
}
```
Note that `Dimensions` is a list, since all arrays in MATLAB are (at least potentially) multi-dimensional. However, `ConvertToDoubleArray()` and `ConvertToComplexArray()` return flat arrays, arranging all multi-dimensional data in columns (MATLAB-style). This functions return `null` if conversion failed (for example, if you tried to apply it to a structure array, or cell array).
Note that `Dimensions` is a list, since all arrays in MATLAB are (at least
potentially) multi-dimensional. However, `ConvertToDoubleArray()` and
`ConvertToComplexArray()` return flat arrays, arranging all multi-dimensional
data in columns (MATLAB-style). This functions return `null` if conversion
failed (for example, if you tried to apply it to a structure array, or cell
array).
## Numerical and logical arrays
### Numerical and logical arrays
The simplest type of array is a numerical array, which implements the `IArrayOf<T>` interface, where `T` is a numerical type, i. e., one of `Int8`, `UInt8`, `Int16`, `UInt16`, `Int32`, `UInt32`, `Int64`, `UInt64`, `Single`, `Double`. Arrays can contain complex values, which are just pairs of ordinary numbers. These pairs of `Double`s are represented by `System.Numerics.Complex`, and pairs of other numerical types are represented by a simple `ComplexOf<T>` struct, which has two properties:
The simplest type of array is a numerical array, which implements the
`IArrayOf<T>` interface, where `T` is a numerical type, i. e., one of `Int8`,
`UInt8`, `Int16`, `UInt16`, `Int32`, `UInt32`, `Int64`, `UInt64`, `Single`,
`Double`. Arrays can contain complex values, which are just pairs of
ordinary numbers. These pairs of `Double`s are represented by
`System.Numerics.Complex`, and pairs of other numerical types are
represented by a simple `ComplexOf<T>` struct, which has two properties:
```csharp
public struct ComplexOf<T> : IEquatable<ComplexOf<T>>
where T : struct
@ -64,9 +95,18 @@ public struct ComplexOf<T> : IEquatable<ComplexOf<T>>
}
```
All of this means that you can also have an `IArrayOf<T>` for `T` being `ComplexOf<Int8>`, `ComplexOf<UInt8>`, `ComplexOf<Int16>`, `ComplexOf<UInt16>`, `ComplexOf<Int32>`, `ComplexOf<UInt32>`, `ComplexOf<Int64>`, `ComplexOf<UInt64>`, `ComplexOf<Single>`, and, of course, `Complex` (note that we don't use `ComplexOf<Double>`). Finally, you can access a logical array as `IArrayOf<Boolean>`.
All of this means that you can also have an `IArrayOf<T>` for `T` being
`ComplexOf<Int8>`, `ComplexOf<UInt8>`, `ComplexOf<Int16>`, `ComplexOf<UInt16>`,
`ComplexOf<Int32>`, `ComplexOf<UInt32>`, `ComplexOf<Int64>`,
`ComplexOf<UInt64>`, `ComplexOf<Single>`, and, of course, `Complex` (note that
we don't use `ComplexOf<Double>`). Finally, you can access a logical array as
`IArrayOf<Boolean>`.
The `IArrayOf<T>` interface allows you to refer to a specific element by using a (multi-dimensional) indexer, or get all data at once as a flat array (multidimensional arrays get converted to flat using MATLAB conventions). Indexes start with 0 (note that in MATLAB they start with 1, so there is a shift in notation).
The `IArrayOf<T>` interface allows you to refer to a specific element by using a
(multi-dimensional) indexer, or get all data at once as a flat array
(multidimensional arrays get converted to flat using MATLAB conventions).
Indexes start with 0 (note that in MATLAB they start with 1, so there is a
shift in notation).
```csharp
public interface IArrayOf<T> : IArray
{
@ -74,26 +114,46 @@ public interface IArrayOf<T> : IArray
T this[params int[] list] { get; set; }
}
```
You can use a one-dimensional indexer or a multi-dimensional one, which is consistent with MATLAB notation. For example, a 2×3 array named `a` has elements `a[0, 0]`, `a[1, 0]` (first column), `a[0, 1]`, `a[1, 1]` (second column), `a[0, 2]`, `a[1, 2]` (third column), which can also be accessed as `a[0]`, `a[1]`, `a[2]`, `a[3]`, `a[4]`, and `a[5]`, respectively.
You can use a one-dimensional indexer or a multi-dimensional one, which is
consistent with MATLAB notation. For example, a 2×3 array named `a` has elements
`a[0, 0]`, `a[1, 0]` (first column), `a[0, 1]`, `a[1, 1]` (second column), `a[0,
2]`, `a[1, 2]` (third column), which can also be accessed as `a[0]`, `a[1]`, `a
[2]`, `a[3]`, `a[4]`, and `a[5]`, respectively.
## Cell arrays
### Cell arrays
Cell array is just an array of arrays, so `ICellArray` implements `IArrayOf<IArray>`, and adds nothing to it. This means that you can refer to specific cells in a cell array by using the indexer, or by inspecting the `Data` array described in the previous section.
Cell array is just an array of arrays, so `ICellArray` implements
`IArrayOf<IArray>`, and adds nothing to it. This means that you can refer to
specific cells in a cell array by using the indexer, or by inspecting the
`Data` array described in the previous section.
## Char arrays
### Char arrays
Char arrays implement `IArrayOf<char>`, so you can refer to individual chars in it via an indexer. Often a char array is used to carry a string, so there is a property for that:
Char arrays implement `IArrayOf<char>`, so you can refer to individual chars in
it via an indexer. Often a char array is used to carry a string, so there is
a property for that:
```csharp
public interface ICharArray : IArrayOf<char>
{
string String { get; }
}
```
This can be slightly weird for multi-dimensional arrays: the characters are stuffed into this string by columns (the same way the numerical array elements are flattened into a one-dimensional array). Moreover, each character array you read from a file actually implements either `IArrayOf<UInt8>`, or `IArrayOf<UInt16>`, depending on whether it was stored as a UTF-8 or UTF-16 encoded string. Characters arrays produced by MatFileHandler are always encoded as UTF-16.
This can be slightly weird for multi-dimensional arrays: the characters are
stuffed into this string by columns (the same way the numerical array elements
are flattened into a one-dimensional array). Moreover, each character array you
read from a file actually implements either `IArrayOf<UInt8>`, or
`IArrayOf<UInt16>`, depending on whether it was stored as a UTF-8 or UTF-16
encoded string. Characters arrays produced by MatFileHandler are always encoded
as UTF-16.
## Structure arrays
### Structure arrays
Structure arrays have elements that are indexed not only by their positions in the array, but also by structure fields. For example, a 1×2 structure array `s` with fields `x` and `y` has four elements: `s(1).x`, `s(1).y`, `s(2).x`, `s(2).y` (in MATLAB notation). This means that if you only specify the numerical indices, you get a dictionary that maps `string` to `IArray`; in order to reach a specific element, you need to provide both the indices and the field name:
Structure arrays have elements that are indexed not only by their positions in
the array, but also by structure fields. For example, a 1×2 structure array `s`
with fields `x` and `y` has four elements: `s(1).x`, `s(1).y`, `s(2).x`, `s
(2).y` (in MATLAB notation). This means that if you only specify the numerical
indices, you get a dictionary that maps `string` to `IArray`; in order to reach
a specific element, you need to provide both the indices and the field name:
```csharp
public interface IStructureArray : IArrayOf<IReadOnlyDictionary<string, IArray>>
{
@ -103,9 +163,10 @@ public interface IStructureArray : IArrayOf<IReadOnlyDictionary<string, IArray>>
```
Here `FieldNames` gives you a list of all fields in the structure.
## Sparse arrays
### Sparse arrays
Sparse array is like a numerical array, but not all of the values in it have to be specified; the rest are assumed to be 0.
Sparse array is like a numerical array, but not all of the values in it have to
be specified; the rest are assumed to be 0.
```csharp
public interface ISparseArrayOf<T> : IArrayOf<T>
where T : struct
@ -113,23 +174,99 @@ public interface ISparseArrayOf<T> : IArrayOf<T>
new IReadOnlyDictionary<(int, int), T> Data { get; }
}
```
Since `ISparseArrayOf<T>` implements `IArrayOf<T>`, you still can access all the elements in a sparse array (you'll get 0 when the element is not present). Alternatively, you can get a dictionary of all (possibly) non-zero elements. MATLAB only supports double, complex, and logical sparse arrays, so `T` here can be `Double`, `Complex` or `Boolean` (which, of course, uses `false` as the default value).
Since `ISparseArrayOf<T>` implements `IArrayOf<T>`, you still can access all the
elements in a sparse array (you'll get 0 when the element is not present).
Alternatively, you can get a dictionary of all (possibly) non-zero elements.
MATLAB only supports double, complex, and logical sparse arrays, so `T` here
can be `Double`, `Complex` or `Boolean` (which, of course, uses `false` as
the default value).
### Object arrays
Matlab objects are similar to structures in that they have some data associated
with fields. As an example, consider a simple `Point` class defined in Matlab as
```matlab
classdef Point
properties
x
y
end
end
```
We omit any methods (and constructos) such a class might have, because they are
not stored when you save an object of a class into a `.mat` file.
Imagine that you have a `1x2 Point` object array `p` (an array of two points)
where the first point has `x=3`, `y=5`, and the second point has `x=-2`, `y=6`.
You can load a mat file containing the variable `p` as usual (using
`MatFileReader`) and access the data using the following interface:
```csharp
public interface IMatObject : IArrayOf<IReadOnlyDictionary<string, IArray>>
{
string ClassName { get; }
IEnumerable<string> FieldNames { get; }
IArray this[string field, params int[] list] { get; set; }
}
```
As you can see, the interface is very similar to `IStructureArray`. The only
addition is the `ClassName` string, which returns the name of object's class
(in our case that would be `Point`). Otherwise, the idea is the same.
In our example, if we load the `.mat` file containing the variable `p` into a
variable named `matFile`, we could then use
```csharp
var matObject = matFile["p"].Value as IMatObject
```
and access the values: `matObject["x", 0] = 3`, `matObject["y", 1] = 6`,
`matObject[1]["x"] = -2`, and so on.
### Tables
Tables in Matlab are just objects of type `table`, so you could use the
interface `IMatObject` described above and get access to all the data in a table
stored in a `.mat` file. However, this is not very convenient, since all the
actual data in a table is stored in one field called `data`, and the
properties are scattered across other fields.
This is why `MatFileHandler` provides a simple wrapper class to work with
tables:
```
public class TableAdapter
{
public TableAdapter(IArray array);
public string Description { get; }
public int NumberOfRows { get; }
public int NumberOfVariables { get; }
public string[] RowNames { get; }
public string[] VariableNames { get; }
public IArray this[string variableName] { get; }
}
```
The constructor creates a `TableAdapter` from an object that you read from a
file. You can access table's description field, query number and names of the
rows and variables of the table, and access all data associated with a single
variable. This accessor returns an array (or a cell array) that has the same
number of rows as table's `NumberOfRows`, and contains values for a given
variable from all the rows (so this is equivalent to Matlab's `t.variable` for
a table `t` having a variable named `variable`).
## Writing a .mat file
After reading a file into `IMatFile matFile`, you can alter some values using the described interfaces, and write the result to a new file:
After reading a file into `IMatFile matFile`, you can alter some values using
the described interfaces, and write the result to a new file:
```csharp
using (var fileStream = new System.IO.FileStream("output.mat", System.IO.FileMode.Create)) {
var writer = new MatFileWriter(fileStream);
writer.Write(matFile);
}
```
By default, all variables are written in a compressed format; you can turn that off by using another constructor for `MatFileWriter`:
By default, all variables are written in a compressed format; you can turn that
off by using another constructor for `MatFileWriter`:
```csharp
var writer = new MatFileWriter(fileStream, new MatFileWriterOptions { UseCompression = CompressionUsage.Never });
```
Another option is to create a file from scratch. You can do it with `DataBuilder` class:
Another option is to create a file from scratch. You can do it with
`DataBuilder` class:
```csharp
public class DataBuilder
@ -149,4 +286,9 @@ public class DataBuilder
public IMatFile NewFile(IEnumerable<IVariable> variables);
}
```
Numerical/logical arrays can be created with `NewArray<T>()` using the provided data; char arrays can be created with `NewCharArray()` using a string. All other types of arrays are created empty. Then you can wrap an array into a variable with `NewVariable()`, and put a bunch of variables into a file using `NewFile()`. The resulting file can be written to a stream using `MatFileWriter`, as shown above.
Numerical/logical arrays can be created with `NewArray<T>()` using the provided
data; char arrays can be created with `NewCharArray()` using a string. All
other types of arrays are created empty. Then you can wrap an array into a
variable with `NewVariable()`, and put a bunch of variables into a file using
`NewFile()`. The resulting file can be written to a stream using
`MatFileWriter`, as shown above.