topk

topk(data=None, axis=_Null, k=_Null, ret_typ=_Null, is_ascend=_Null, dtype=_Null, out=None, name=None, **kwargs)

Returns the indices of the top k elements in an input array along the given

axis (by default). If ret_type is set to ‘value’ returns the value of top k elements (instead of indices). In case of ret_type = ‘both’, both value and index would be returned. The returned elements will be sorted.

Examples:

x = [[ 0.3,  0.2,  0.4],
     [ 0.1,  0.3,  0.2]]

// returns an index of the largest element on last axis
topk(x) = [[ 2.],
           [ 1.]]

// returns the value of top-2 largest elements on last axis
topk(x, ret_typ='value', k=2) = [[ 0.4,  0.3],
                                 [ 0.3,  0.2]]

// returns the value of top-2 smallest elements on last axis
topk(x, ret_typ='value', k=2, is_ascend=1) = [[ 0.2 ,  0.3],
                                             [ 0.1 ,  0.2]]

// returns the value of top-2 largest elements on axis 0
topk(x, axis=0, ret_typ='value', k=2) = [[ 0.3,  0.3,  0.4],
                                         [ 0.1,  0.2,  0.2]]

// flattens and then returns list of both values and indices
topk(x, ret_typ='both', k=2) = [[[ 0.4,  0.3], [ 0.3,  0.2]] ,  [[ 2.,  0.], [ 1.,  2.]]]

Defined in src/operator/tensor/ordering_op.cc:L68

Parameters:

data : ndarray

The input array

axis : int or None, optional, default=’-1’

Axis along which to choose the top k indices. If not given, the flattened array is used. Default is -1.

k : int, optional, default=’1’

Number of top elements to select, should be always smaller than or equal to the element number in the given axis. A global sort is performed if set k < 1.

ret_typ : {‘both’, ‘indices’, ‘mask’, ‘value’},optional, default=’indices’

The return type.

“value” means to return the top k values, “indices” means to return the indices of the top k values, “mask” means to return a mask array containing 0 and 1. 1 means the top k values. “both” means to return a list of both values and indices of top k elements.

is_ascend : boolean, optional, default=0

Whether to choose k largest or k smallest elements. Top K largest elements will be chosen if set to false.

dtype : {‘float16’, ‘float32’, ‘float64’, ‘int32’, ‘int64’, ‘uint8’},optional, default=’float32’

DType of the output indices when ret_typ is “indices” or “both”. An error will be raised if the selected data type cannot precisely represent the indices.

out : ndarray, optional

The output ndarray to hold the result.

Returns:

out : ndarray or list of ndarrays

The output of this function.