TensorFlow.NET/src/TensorFlowNET.Core/Numpy/Slice.cs at master · feelsyt/TensorFlow.NET · GitHub

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using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Text.RegularExpressions;

namespace Tensorflow

{

/// <summary>

/// NDArray can be indexed using slicing

/// A slice is constructed by start:stop:step notation

///

/// Examples:

///

/// a[start:stop] # items start through stop-1

/// a[start:] # items start through the rest of the array

/// a[:stop] # items from the beginning through stop-1

///

/// The key point to remember is that the :stop value represents the first value that is not

/// in the selected slice. So, the difference between stop and start is the number of elements

/// selected (if step is 1, the default).

///

/// There is also the step value, which can be used with any of the above:

/// a[:] # a copy of the whole array

/// a[start:stop:step] # start through not past stop, by step

///

/// The other feature is that start or stop may be a negative number, which means it counts

/// from the end of the array instead of the beginning. So:

/// a[-1] # last item in the array

/// a[-2:] # last two items in the array

/// a[:-2] # everything except the last two items

/// Similarly, step may be a negative number:

///

/// a[::- 1] # all items in the array, reversed

/// a[1::- 1] # the first two items, reversed

/// a[:-3:-1] # the last two items, reversed

/// a[-3::- 1] # everything except the last two items, reversed

///

/// NumSharp is kind to the programmer if there are fewer items than

/// you ask for. For example, if you ask for a[:-2] and a only contains one element, you get an

/// empty list instead of an error.Sometimes you would prefer the error, so you have to be aware

/// that this may happen.

///

/// Adapted from Greg Hewgill's answer on Stackoverflow: https://stackoverflow.com/questions/509211/understanding-slice-notation

///

/// Note: special IsIndex == true

/// It will pick only a single value at Start in this dimension effectively reducing the Shape of the sliced matrix by 1 dimension.

/// It can be used to reduce an N-dimensional array/matrix to a (N-1)-dimensional array/matrix

///

/// Example:

/// a=[[1, 2], [3, 4]]

/// a[:, 1] returns the second column of that 2x2 matrix as a 1-D vector

/// </summary>

public class Slice

{

/// <summary>

/// return : for this dimension

/// </summary>

public static readonly Slice All = new Slice(null, null);

/// <summary>

/// return 0:0 for this dimension

/// </summary>

public static readonly Slice None = new Slice(0, 0, 1);

/// <summary>

/// fill up the missing dimensions with : at this point, corresponds to ...

/// </summary>

public static readonly Slice Ellipsis = new Slice(0, 0, 1) { IsEllipsis = true };

/// <summary>

/// insert a new dimension at this point

/// </summary>

public static readonly Slice NewAxis = new Slice(0, 0, 1) { IsNewAxis = true };

/// <summary>

/// return exactly one element at this dimension and reduce the shape from n-dim to (n-1)-dim

/// </summary>

/// <param name="index"></param>

/// <returns></returns>

public static Slice Index(int index) => new Slice(index, index + 1) { IsIndex = true };

///// <summary>

///// return multiple elements for this dimension specified by the given index array (or boolean mask array)

///// </summary>

///// <param name="index_array_or_mask"></param>

///// <returns></returns>

//[MethodImpl(MethodImplOptions.AggressiveInlining)]

//public static Slice Select(NDArray index_array_or_mask) => new Slice(null, null) { Selection=index_array_or_mask };

public int? Start;

public int? Stop;

public int Step;

public bool IsIndex;

public bool IsEllipsis;

public bool IsNewAxis;

///// <summary>

///// Array of integer indices to select elements by index extraction or boolean values to select by masking the elements of the given dimension.

///// </summary>

//public NDArray Selection = null;

/// <summary>

/// Length of the slice.

/// <remarks>

/// The length is not guaranteed to be known for i.e. a slice like ":". Make sure to check Start and Stop

/// for null before using it</remarks>

/// </summary>

public int? Length => Stop - Start;

/// <summary>

/// ndarray can be indexed using slicing

/// slice is constructed by start:stop:step notation

/// </summary>

/// <param name="start">Start index of the slice, null means from the start of the array</param>

/// <param name="stop">Stop index (first index after end of slice), null means to the end of the array</param>

/// <param name="step">Optional step to select every n-th element, defaults to 1</param>

public Slice(int? start = null, int? stop = null, int step = 1, bool isIndex = false)

{

Start = start;

Stop = stop;

Step = step;

IsIndex = isIndex;

}

public Slice(string slice_notation)

{

Parse(slice_notation);

}

/// <summary>

/// Parses Python array slice notation and returns an array of Slice objects

/// </summary>

public static Slice[] ParseSlices(string multi_slice_notation)

{

return Regex.Split(multi_slice_notation, @",\s*").Where(s => !string.IsNullOrWhiteSpace(s)).Select(token => new Slice(token)).ToArray();

}

/// <summary>

/// Creates Python array slice notation out of an array of Slice objects (mainly used for tests)

/// </summary>

public static string FormatSlices(params Slice[] slices)

{

return string.Join(",", slices.Select(s => s.ToString()));

}

private void Parse(string slice_notation)

{

if (string.IsNullOrEmpty(slice_notation))

throw new ArgumentException("Slice notation expected, got empty string or null");

var match = Regex.Match(slice_notation, @"^\s*((?'start'[+-]?\s*\d+)?\s*:\s*(?'stop'[+-]?\s*\d+)?\s*(:\s*(?'step'[+-]?\s*\d+)?)?|(?'index'[+-]?\s*\d+)|(?'ellipsis'\.\.\.)|(?'newaxis'(np\.)?newaxis))\s*$");

if (!match.Success)

throw new ArgumentException($"Invalid slice notation: '{slice_notation}'");

if (match.Groups["ellipsis"].Success)

{

Start = 0;

Stop = 0;

Step = 1;

IsEllipsis = true;

return;

}

if (match.Groups["newaxis"].Success)

{

Start = 0;

Stop = 0;

Step = 1;

IsNewAxis = true;

return;

}

if (match.Groups["index"].Success)

{

if (!int.TryParse(Regex.Replace(match.Groups["index"].Value ?? "", @"\s+", ""), out var start))

throw new ArgumentException($"Invalid value for index: '{match.Groups["index"].Value}'");

Start = start;

Stop = start + 1;

Step = 1; // special case for dimensionality reduction by picking a single element

IsIndex = true;

return;

}

var start_string = Regex.Replace(match.Groups["start"].Value ?? "", @"\s+", ""); // removing spaces from match to be able to parse what python allows, like: "+ 1" or "- 9";

var stop_string = Regex.Replace(match.Groups["stop"].Value ?? "", @"\s+", "");

var step_string = Regex.Replace(match.Groups["step"].Value ?? "", @"\s+", "");

if (string.IsNullOrWhiteSpace(start_string))

Start = null;

else

{

if (!int.TryParse(start_string, out var start))

throw new ArgumentException($"Invalid value for start: {start_string}");

Start = start;

}

if (string.IsNullOrWhiteSpace(stop_string))

Stop = null;

else

{

if (!int.TryParse(stop_string, out var stop))

throw new ArgumentException($"Invalid value for start: {stop_string}");

Stop = stop;

}

if (string.IsNullOrWhiteSpace(step_string))

Step = 1;

else

{

if (!int.TryParse(step_string, out var step))

throw new ArgumentException($"Invalid value for start: {step_string}");

Step = step;

}

#region Equality comparison

public static bool operator ==(Slice a, Slice b)

{

if (ReferenceEquals(a, b))

return true;

if (a is null || b is null)

return false;

return a.Start == b.Start && a.Stop == b.Stop && a.Step == b.Step;

}

public static bool operator !=(Slice a, Slice b)

{

return !(a == b);

}

public override bool Equals(object obj)

{

if (obj == null)

return false;

if (obj.GetType() != typeof(Slice))

return false;

var b = (Slice)obj;

return Start == b.Start && Stop == b.Stop && Step == b.Step;

}

public override int GetHashCode()

{

return ToString().GetHashCode();

}

#endregion

public override string ToString()

{

if (IsIndex)

return $"{Start ?? 0}";

else if (IsNewAxis)

return "np.newaxis";

else if (IsEllipsis)

return "...";

var optional_step = Step == 1 ? "" : $":{Step}";

return $"{(Start == 0 ? "" : Start.ToString())}:{(Stop == null ? "" : Stop.ToString())}{optional_step}";

}

// return the size of the slice, given the data dimension on this axis

// note: this works only with sanitized shapes!

public int GetSize()

{

var astep = Math.Abs(Step);

return (Math.Abs(Start.Value - Stop.Value) + (astep - 1)) / astep;

}

#region Operators

public static Slice operator ++(Slice a)

{

if (a.Start.HasValue)

a.Start++;

if (a.Stop.HasValue)

a.Stop++;

return a;

}

public static Slice operator --(Slice a)

{

if (a.Start.HasValue)

a.Start--;

if (a.Stop.HasValue)

a.Stop--;

return a;

}

public static implicit operator Slice(int index) => Slice.Index(index);

public static implicit operator Slice(string slice) => new Slice(slice);

//public static implicit operator Slice(NDArray selection) => Slice.Select(selection);

#endregion

}

TensorFlow.NET/src/TensorFlowNET.Core/Numpy/Slice.cs at master · feelsyt/TensorFlow.NET · GitHub

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