/// <summary>
/// [Pure] Projects each element of a NdArray into a new form.
/// </summary>
/// <typeparam name="TSource"> The type of the elements of <paramref name="ndarray"/>. </typeparam>
/// <typeparam name="TResult"> The type of the value returned by <paramref name="selector"/>. </typeparam>
/// <param name="ndarray"> A NdArray for values to invoke a transform function on. </param>
/// <param name="selector"> A transform function to apply to each element. </param>
/// <param name="strategy">
/// [nullable] A strategy object to iterate calculation for each element.
/// <c>null</c> means to use <see cref="IterationStrategy.Default"/>.
/// </param>
/// <returns> [<c>$ReturnValue.Shape == NdArray.Shape</c>] </returns>
public static NdArray <TResult> Select <TSource, TResult>(
this NdArray <TSource> ndarray,
Func <TSource, TResult> selector,
IIterationStrategy?strategy = default)
{
Guard.AssertArgumentNotNull(ndarray, nameof(ndarray));
Guard.AssertArgumentNotNull(selector, nameof(selector));
var len = ndarray.Length;
var entity = new RawNdArrayImpl <TResult>(ndarray.Shape);
var array = entity.Buffer;
if (strategy is null || strategy is IterationStrategy)
{
if (ndarray.Entity is RawNdArrayImpl <TSource> raw)
{
for (var i = 0; i < len; ++i)
{
array.Span[i] = selector(raw.Buffer.Span[i]);
}
}
else
{
for (var i = 0; i < len; ++i)
{
array.Span[i] = selector(ndarray.GetItem(i));
}
}
}
/// <summary>
/// When <typeparamref name="T"/> is primitive type, saves <see cref="NdArray{T}"/> instance to .npy binary.
/// </summary>
/// <param name="stream"></param>
/// <param name="ndArray"></param>
/// <exception cref="NotSupportedException"></exception>
/// <typeparam name="T"> A primitive type. </typeparam>
public static void Save <T>(Stream stream, NdArray <T> ndArray)
where T : unmanaged
=> SaveCore(stream,
ndArray,
DType.UInt16,
(i, buf) => LittleEndianConv.TryWritePrimitive(buf.AsSpan(), ndArray.GetItem(i)));