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NAG Toolbox: nag_sort_charvec_rank (m01dc)

Purpose

nag_sort_charvec_rank (m01dc) ranks a vector of character data in ASCII or reverse ASCII order of a specified substring.

Syntax

[irank, ifail] = m01dc(ch, m1, l1, l2, order, 'm2', m2)
[irank, ifail] = nag_sort_charvec_rank(ch, m1, l1, l2, order, 'm2', m2)

Description

nag_sort_charvec_rank (m01dc) 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 1010. The ranking is stable: equal elements preserve their ordering in the input data.
Only the substring (l1:l2) of each element of the array ch is used to determine the rank order.

References

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

Parameters

Compulsory Input Parameters

1:     ch(m2) – cell array of strings
m2, the dimension of the array, must satisfy the constraint m2m1m2m1.
Elements m1 to m2 of ch must contain character data to be ranked.
Constraint: the length of each element of ch must not exceed 255255.
2:     m1 – int64int32nag_int scalar
The index of the first element of ch to be ranked.
Constraint: m1 > 0m1>0.
3:     l1 – int64int32nag_int scalar
4:     l2 – int64int32nag_int scalar
Only the substring (l1:l2) of each element of ch is to be used in determining the rank order.
Constraint: 0 < l1l2LEN(ch(1))0<l1l2LEN(ch1).
5:     order – string (length ≥ 1)
If order = 'A'order='A', the values will be ranked in ASCII order.
If order = 'R'order='R', in reverse ASCII order.
Constraint: order = 'A'order='A' or 'R''R'.

Optional Input Parameters

1:     m2 – int64int32nag_int scalar
Default: The dimension of the array ch.
The index of the last element of ch to be ranked.
Constraint: m2m1m2m1.

Input Parameters Omitted from the MATLAB Interface

None.

Output Parameters

1:     irank(m2) – int64int32nag_int array
Elements m1 to m2 of irank contain the ranks of the corresponding elements of ch. Note that the ranks are in the range m1 to m2: thus, if ch(i)chi is the first element in the rank order, irank(i)iranki is set to m1.
2:     ifail – int64int32nag_int scalar
ifail = 0ifail=0 unless the function detects an error (see [Error Indicators and Warnings]).

Error Indicators and Warnings

Errors or warnings detected by the function:
  ifail = 1ifail=1
On entry,m2 < 1m2<1,
orm1 < 1m1<1,
orm1 > m2m1>m2,
orl2 < 1l2<1,
orl1 < 1l1<1,
orl1 > l2l1>l2,
orl2 > LEN(ch(1))l2>LEN(ch1).
  ifail = 2ifail=2
On entry,order is not 'A' or 'R'.
  ifail = 3ifail=3
On entry,the length of each element of ch exceeds 255255.

Accuracy

Not applicable.

Further Comments

The average time taken by the function is approximately proportional to n × log(n)n×log(n), where n = m2m1 + 1n=m2-m1+1.
The function relies on the Fortran intrinsic functions LLT and LGT to order characters according to the ASCII collating sequence.

Example

function nag_sort_charvec_rank_example
ch = {'A02AAF   289'; ...
      'A02ABF   523'; ...
      'A02ACF   531'; ...
      'C02ADF   169'; ...
      'C02AEF   599'; ...
      'C05ADF  1351'; ...
      'C05AGF   240'; ...
      'C05AJF   136'; ...
      'C05AVF   211'; ...
      'C05AXF   183'; ...
      'C05AZF  2181'};
m1 = int64(1);
l1 = int64(7);
l2 = int64(12);
order = 'Reverse ASCII';
[irank, ifail] = nag_sort_charvec_rank(ch, m1, l1, l2, order)
 

irank =

                    6
                    5
                    4
                   10
                    3
                    2
                    7
                   11
                    8
                    9
                    1


ifail =

                    0


function m01dc_example
ch = {'A02AAF   289'; ...
      'A02ABF   523'; ...
      'A02ACF   531'; ...
      'C02ADF   169'; ...
      'C02AEF   599'; ...
      'C05ADF  1351'; ...
      'C05AGF   240'; ...
      'C05AJF   136'; ...
      'C05AVF   211'; ...
      'C05AXF   183'; ...
      'C05AZF  2181'};
m1 = int64(1);
l1 = int64(7);
l2 = int64(12);
order = 'Reverse ASCII';
[irank, ifail] = m01dc(ch, m1, l1, l2, order)
 

irank =

                    6
                    5
                    4
                   10
                    3
                    2
                    7
                   11
                    8
                    9
                    1


ifail =

                    0



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