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NAG Toolbox: nag_sort_charvec_rank (m01dc)


    1  Purpose
    2  Syntax
    7  Accuracy
    9  Example


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


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


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 10. 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.


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


Compulsory Input Parameters

1:     chm2 – cell array of strings
Elements m1 to m2 of ch must contain character data to be ranked.
Constraint: the length of each element of ch must not exceed 255.
2:     m1 int64int32nag_int scalar
The index of the first element of ch to be ranked.
Constraint: m1>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<l1l2LENch1.
5:     order – string (length ≥ 1)
If order='A', the values will be ranked in ASCII order.
If order='R', in reverse ASCII order.
Constraint: order='A' or '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: m2m1.

Output Parameters

1:     irankm2 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 chi is the first element in the rank order, iranki is set to m1.
2:     ifail int64int32nag_int scalar
ifail=0 unless the function detects an error (see Error Indicators and Warnings).

Error Indicators and Warnings

Errors or warnings detected by the function:
On entry,m2<1,
On entry,order is not 'A' or 'R'.
On entry,the length of each element of ch exceeds 255.
An unexpected error has been triggered by this routine. Please contact NAG.
Your licence key may have expired or may not have been installed correctly.
Dynamic memory allocation failed.


Not applicable.

Further Comments

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


This example reads a file of 12-character records, and ranks them in reverse ASCII order on characters 7 to 12.
function m01dc_example

fprintf('m01dc example results\n\n');

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);

fprintf('Records ranked on columns %2d to %2d\n\n',l1,l2);
fprintf('   Data         Ranks\n\n');
for i = 1:numel(ch)

m01dc example results

Records ranked on columns  7 to 12

   Data         Ranks

A02AAF   289      6
A02ABF   523      5
A02ACF   531      4
C02ADF   169     10
C02AEF   599      3
C05ADF  1351      2
C05AGF   240      7
C05AJF   136     11
C05AVF   211      8
C05AXF   183      9
C05AZF  2181      1

PDF version (NAG web site, 64-bit version, 64-bit version)
Chapter Contents
Chapter Introduction
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