示例#1
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        /// <summary>
        ///     Join a sequence of arrays along an existing axis.
        /// </summary>
        /// <param name="axis">The axis along which the arrays will be joined. If axis is None, arrays are flattened before use. Default is 0.</param>
        /// <param name="arrays">The arrays must have the same shape, except in the dimension corresponding to axis (the first, by default).</param>
        /// <returns>The concatenated array.</returns>
        /// <remarks>https://docs.scipy.org/doc/numpy/reference/generated/numpy.concatenate.html</remarks>
        public static NDArray concatenate(NDArray[] arrays, int axis = 0)
        {
            //What we do is we have the axis which is the only dimension that is allowed to be different
            //We need to perform a check if the dimensions actually match.
            //After we have the axis ax=1 where shape is (3,ax,3) - ax is the only dimension that can vary.
            //So if we got input of (3,5,3) and (3,1,3), we create a return shape of (3,6,3).
            //We perform the assignment by iterating a slice: (:,n,:) on src and dst where dst while n of dst grows as we iterate all arrays.

            if (arrays == null)
            {
                throw new ArgumentNullException(nameof(arrays));
            }

            if (arrays.Length == 0)
            {
                throw new ArgumentException("Value cannot be an empty collection.", nameof(arrays));
            }

            if (arrays.Length == 1)
            {
                return(arrays[0]);
            }

            var first      = arrays[0];
            var firstShape = (int[])first.shape.Clone();

            while (axis < 0)
            {
                axis = first.ndim + axis; //translate negative axis
            }
            int        i, j;
            int        axisSize = 0; //accumulated shape[axis] size for return shape.
            NPTypeCode retType  = first.GetTypeCode;

            foreach (var src in arrays)
            {
                //accumulate the concatenated axis
                var shape = src.shape;
                axisSize += shape[axis];

                if (ReferenceEquals(src, first))
                {
                    continue;
                }

                var srcType = src.GetTypeCode;

                //resolve what the return type should be and should we perform casting.
                if (first.GetTypeCode != srcType)
                {
                    if (srcType.CompareTo(retType) == 1)
                    {
                        retType = srcType;
                    }
                }

                if (shape.Length != first.ndim)
                {
                    throw new IncorrectShapeException("all the input arrays must have same number of dimensions.");
                }

                //verify the shapes are equal
                for (j = 0; j < shape.Length; j++)
                {
                    if (axis == j)
                    {
                        continue;
                    }

                    if (shape[j] != firstShape[j])
                    {
                        throw new IncorrectShapeException("all the input array dimensions except for the concatenation axis must match exactly.");
                    }
                }
            }

            //prepare return shape
            firstShape[axis] = axisSize;
            var retShape = new Shape(firstShape);

            var dst         = new NDArray(retType, retShape);
            var accessorDst = new Slice[retShape.NDim];
            var accessorSrc = new Slice[retShape.NDim];

            for (i = 0; i < accessorDst.Length; i++)
            {
                accessorSrc[i] = accessorDst[i] = Slice.All;
            }

            accessorSrc[axis] = Slice.Index(0);
            accessorDst[axis] = Slice.Index(0);

            foreach (var src in arrays)
            {
                var len = src.shape[axis];
                for (i = 0; i < len; i++)
                {
                    var writeTo   = dst[accessorDst];
                    var writeFrom = src[accessorSrc];
                    MultiIterator.Assign(writeTo.Storage, writeFrom.Storage);
                    accessorSrc[axis]++;
                    accessorDst[axis]++; //increment every step
                }

                accessorSrc[axis] = Slice.Index(0); //reset src
            }

            return(dst);
        }