naginterfaces.library.sort.realvec_​rank

naginterfaces.library.sort.realvec_rank(rv, m1, order)

realvec_rank ranks a vector of float numbers in ascending or descending order.

For full information please refer to the NAG Library document for m01da

https://support.nag.com/numeric/nl/nagdoc_30.3/flhtml/m01/m01daf.html

Parameters

rvfloat, array-like, shape $\left(\text{m2}\right)$

Elements $m1-1$ to $\text{m2}-1$ of $rv$ must contain float values to be ranked.

m1int

Note: this argument represents an array index; the value you supply must be base-1 for compatibility with the NAG Engine.

The index of the first element of $rv$ to be ranked.

orderstr, length 1

If $order=\text{'A'}$, the values will be ranked in ascending (i.e., nondecreasing) order.

If $order=\text{'D'}$, into descending order.

Returns

irankint, ndarray, shape $\left(\text{m2}\right)$

Elements $m1-1$ to $\text{m2}-1$ of $irank$ contain the ranks of the corresponding elements of $rv$. Note that the ranks are in the range $m1$ to $\text{m2}$: thus, if $rv[i-1]$ is the first element in the rank order, $irank[i-1]$ is set to $m1$.

Raises

NagValueError

(errno $1$)

On entry, $m1=⟨value⟩$ and $\text{m2}=⟨value⟩$.

Constraint: $m1\le \text{m2}$.

(errno $1$)

On entry, $m1=⟨value⟩$.

Constraint: $m1\ge 1$.

(errno $1$)

On entry, $\text{m2}=⟨value⟩$.

Constraint: $\text{m2}\ge 1$.

(errno $2$)

On entry, $order$ has an illegal value: $order=⟨value⟩$.

Notes

No equivalent traditional C interface for this routine exists in the NAG Library.

realvec_rank uses a variant of list-merging, as described on pages 165–166 in Knuth (1973). The function takes advantage of natural ordering in the data, and uses a simple list insertion in a preparatory pass to generate ordered lists of length at least $10$. The ranking is stable: equal elements preserve their ordering in the input data.

References

Knuth, D E, 1973, The Art of Computer Programming (Volume 3), (2nd Edition), Addison–Wesley