[Numpy] Numpy operator diff (apache#15906)

* numpy diff operator implemented

append and prepend not supported yet

remove the prepend and append checking interface from the backend

refine the code, enrich the test set and all tests passed

registered the diff operator into npi scope

all tests passed

comments and minor modification

format codes and fix warning for sanity check

minor modification for sanity check

fix sanity

fix the tolerance bound of testing np.diff

resolve minor coding style issue

replace the given tests by random picking

minor fix

* interoperability test added

python/mxnet/ndarray/numpy/_op.py

@@ -38,7 +38,7 @@
            'std', 'var', 'indices', 'copysign', 'ravel', 'hanning', 'hamming', 'blackman', 'flip',
            'around', 'hypot', 'rad2deg', 'deg2rad', 'unique', 'lcm', 'tril', 'identity', 'take',
            'ldexp', 'vdot', 'inner', 'outer', 'equal', 'not_equal', 'greater', 'less', 'greater_equal', 'less_equal',
-           'hsplit', 'rot90', 'einsum', 'true_divide', 'nonzero', 'shares_memory', 'may_share_memory']
+           'hsplit', 'rot90', 'einsum', 'true_divide', 'nonzero', 'shares_memory', 'may_share_memory', 'diff']
 
 
 @set_module('mxnet.ndarray.numpy')
@@ -4983,3 +4983,51 @@ def may_share_memory(a, b, max_work=None):
     - Actually it is same as `shares_memory` in MXNet DeepNumPy
     """
     return _npi.share_memory(a, b).item()
+
+
+def diff(a, n=1, axis=-1, prepend=None, append=None):
+    r"""
+    numpy.diff(a, n=1, axis=-1, prepend=<no value>, append=<no value>)
+
+    Calculate the n-th discrete difference along the given axis.
+
+    Parameters
+    ----------
+    a : ndarray
+        Input array
+    n : int, optional
+        The number of times values are differenced. If zero, the input is returned as-is.
+    axis : int, optional
+        The axis along which the difference is taken, default is the last axis.
+    prepend, append : ndarray, optional
+        Not supported yet
+
+    Returns
+    -------
+    diff : ndarray
+        The n-th differences.
+        The shape of the output is the same as a except along axis where the dimension is smaller by n.
+        The type of the output is the same as the type of the difference between any two elements of a.
+
+    Examples
+    --------
+    >>> x = np.array([1, 2, 4, 7, 0])
+    >>> np.diff(x)
+    array([ 1,  2,  3, -7])
+    >>> np.diff(x, n=2)
+    array([  1,   1, -10])
+
+    >>> x = np.array([[1, 3, 6, 10], [0, 5, 6, 8]])
+    >>> np.diff(x)
+    array([[2, 3, 4],
+        [5, 1, 2]])
+    >>> np.diff(x, axis=0)
+    array([[-1,  2,  0, -2]])
+
+    Notes
+    -----
+    Optional inputs `prepend` and `append` are not supported yet
+    """
+    if (prepend or append):
+        raise NotImplementedError('prepend and append options are not supported yet')
+    return _npi.diff(a, n=n, axis=axis)

python/mxnet/numpy/multiarray.py

@@ -56,7 +56,7 @@
            'blackman', 'flip', 'around', 'arctan2', 'hypot', 'rad2deg', 'deg2rad', 'unique', 'lcm', 'tril',
            'identity', 'take', 'ldexp', 'vdot', 'inner', 'outer', 'equal', 'not_equal', 'greater', 'less',
            'greater_equal', 'less_equal', 'hsplit', 'rot90', 'einsum', 'true_divide', 'nonzero', 'shares_memory',
-           'may_share_memory']
+           'may_share_memory', 'diff']
 
 # Return code for dispatching indexing function call
 _NDARRAY_UNSUPPORTED_INDEXING = -1
@@ -6975,3 +6975,52 @@ def may_share_memory(a, b, max_work=None):
     - Actually it is same as `shares_memory` in MXNet DeepNumPy
     """
     return _mx_nd_np.may_share_memory(a, b, max_work)
+
+
+def diff(a, n=1, axis=-1, prepend=None, append=None):
+    r"""
+    numpy.diff(a, n=1, axis=-1, prepend=<no value>, append=<no value>)
+
+    Calculate the n-th discrete difference along the given axis.
+
+    Parameters
+    ----------
+    a : ndarray
+        Input array
+    n : int, optional
+        The number of times values are differenced. If zero, the input is returned as-is.
+    axis : int, optional
+        The axis along which the difference is taken, default is the last axis.
+    prepend, append : ndarray, optional
+        Not supported yet
+
+    Returns
+    -------
+    diff : ndarray
+        The n-th differences.
+        The shape of the output is the same as a except along axis where the dimension is smaller by n.
+        The type of the output is the same as the type of the difference between any two elements of a.
+        This is the same as the type of a in most cases.
+
+    Examples
+    --------
+    >>> x = np.array([1, 2, 4, 7, 0])
+    >>> np.diff(x)
+    array([ 1,  2,  3, -7])
+    >>> np.diff(x, n=2)
+    array([  1,   1, -10])
+
+    >>> x = np.array([[1, 3, 6, 10], [0, 5, 6, 8]])
+    >>> np.diff(x)
+    array([[2, 3, 4],
+        [5, 1, 2]])
+    >>> np.diff(x, axis=0)
+    array([[-1,  2,  0, -2]])
+
+    Notes
+    -----
+    Optional inputs `prepend` and `append` are not supported yet
+    """
+    if (prepend or append):
+        raise NotImplementedError('prepend and append options are not supported yet')
+    return _mx_nd_np.diff(a, n=n, axis=axis)

python/mxnet/numpy_dispatch_protocol.py

@@ -130,6 +130,7 @@ def _run_with_array_ufunc_proto(*args, **kwargs):
     'einsum',
     'shares_memory',
     'may_share_memory',
+    'diff',
 ]
 
 

python/mxnet/symbol/numpy/_symbol.py

@@ -40,7 +40,7 @@
            'std', 'var', 'indices', 'copysign', 'ravel', 'hanning', 'hamming', 'blackman', 'flip',
            'around', 'hypot', 'rad2deg', 'deg2rad', 'unique', 'lcm', 'tril', 'identity', 'take',
            'ldexp', 'vdot', 'inner', 'outer', 'equal', 'not_equal', 'greater', 'less', 'greater_equal',
-           'less_equal', 'hsplit', 'rot90', 'einsum', 'true_divide', 'shares_memory', 'may_share_memory']
+           'less_equal', 'hsplit', 'rot90', 'einsum', 'true_divide', 'shares_memory', 'may_share_memory', 'diff']
 
 
 def _num_outputs(sym):
@@ -4629,4 +4629,53 @@ def may_share_memory(a, b, max_work=None):
     return _npi.share_memory(a, b)
 
 
+def diff(a, n=1, axis=-1, prepend=None, append=None):
+    r"""
+    numpy.diff(a, n=1, axis=-1, prepend=<no value>, append=<no value>)
+
+    Calculate the n-th discrete difference along the given axis.
+
+    Parameters
+    ----------
+    a : ndarray
+        Input array
+    n : int, optional
+        The number of times values are differenced. If zero, the input is returned as-is.
+    axis : int, optional
+        The axis along which the difference is taken, default is the last axis.
+    prepend, append : ndarray, optional
+        Not supported yet
+
+    Returns
+    -------
+    diff : ndarray
+        The n-th differences.
+        The shape of the output is the same as a except along axis where the dimension is smaller by n.
+        The type of the output is the same as the type of the difference between any two elements of a.
+        This is the same as the type of a in most cases.
+
+    Examples
+    --------
+    >>> x = np.array([1, 2, 4, 7, 0])
+    >>> np.diff(x)
+    array([ 1,  2,  3, -7])
+    >>> np.diff(x, n=2)
+    array([  1,   1, -10])
+
+    >>> x = np.array([[1, 3, 6, 10], [0, 5, 6, 8]])
+    >>> np.diff(x)
+    array([[2, 3, 4],
+        [5, 1, 2]])
+    >>> np.diff(x, axis=0)
+    array([[-1,  2,  0, -2]])
+
+    Notes
+    -----
+    Optional inputs `prepend` and `append` are not supported yet
+    """
+    if (prepend or append):
+        raise NotImplementedError('prepend and append options are not supported yet')
+    return _npi.diff(a, n=n, axis=axis)
+
+
 _set_np_symbol_class(_Symbol)