naginterfaces.library.sort.charvec_​sort

naginterfaces.library.sort.charvec_sort(ch, m1, l1, l2, order)

charvec_sort rearranges a vector of character data so that a specified substring is in ASCII or reverse ASCII order.

For full information please refer to the NAG Library document for m01cc

https://support.nag.com/numeric/nl/nagdoc_30.2/flhtml/m01/m01ccf.html

Parameters

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

Elements $m1-1$ to $\text{m2}-1$ of $ch$ must contain character data to be sorted.

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 $ch$ to be sorted.

l1int

Only the substring ($l1$:$l2$) of each element of $ch$ is to be used in determining the sorted order.

l2int

Only the substring ($l1$:$l2$) of each element of $ch$ is to be used in determining the sorted order.

orderstr, length 1

If $order=\text{'A'}$, the values will be sorted into ASCII order.

If $order=\text{'R'}$, into reverse ASCII order.

Returns

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

These values are rearranged into sorted order.

Raises

NagValueError

(errno $1$)

On entry, $l2=⟨value⟩$ and $len\left(ch\right[0\left]\right)=⟨value⟩$.

Constraint: $l2\le len\left(ch\right[0\left]\right)$.

(errno $1$)

On entry, $l1=⟨value⟩$ and $l2=⟨value⟩$.

Constraint: $l1\le l2$.

(errno $1$)

On entry, $l1=⟨value⟩$.

Constraint: $l1\ge 1$.

(errno $1$)

On entry, $l2=⟨value⟩$.

Constraint: $l2\ge 1$.

(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: $order=⟨value⟩$.

(errno $3$)

On entry, $len\left(ch\right[0\left]\right)=⟨value⟩$.

Constraint: $len\left(ch\right[0\left]\right)\le 255$.

Notes

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

charvec_sort is based on Singleton’s implementation of the ‘median-of-three’ Quicksort algorithm (see Singleton (1969)), but with two additional modifications. First, small subfiles are sorted by an insertion sort on a separate final pass (see Sedgewick (1978)) Second, if a subfile is partitioned into two very unbalanced subfiles, the larger of them is flagged for special treatment: before it is partitioned, its end points are swapped with two random points within it; this makes the worst case behaviour extremely unlikely.

Only the substring ($l1$:$l2$) of each element of the array $ch$ is used to determine the sorted order, but the entire elements are rearranged into sorted order.

References

Sedgewick, R, 1978, Implementing Quicksort programs, Comm. ACM (21), 847–857

Singleton, R C, 1969, An efficient algorithm for sorting with minimal storage: Algorithm 347, Comm. ACM (12), 185–187