# NAG Library Routine Document

## 1Purpose

m01ecf rearranges a vector of character data into the order specified by a vector of ranks.

## 2Specification

Fortran Interface
 Subroutine m01ecf ( ch, m1, m2,
 Integer, Intent (In) :: m1, m2 Integer, Intent (Inout) :: irank(m2), ifail Character (*), Intent (Inout) :: ch(m2)
#include nagmk26.h
 void m01ecf_ (char ch[], const Integer *m1, const Integer *m2, Integer irank[], Integer *ifail, const Charlen length_ch)

## 3Description

m01ecf is designed to be used typically in conjunction with the M01D ranking routines. After one of the M01D routines has been called to determine a vector of ranks, m01ecf can be called to rearrange a vector of character data into the rank order. If the vector of ranks has been generated in some other way, then m01zbf should be called to check its validity before m01ecf is called.

None.

## 5Arguments

1:     $\mathbf{ch}\left({\mathbf{m2}}\right)$ – Character(*) arrayInput/Output
On entry: elements m1 to m2 of ch must contain character data to be rearranged.
Constraint: the length of each element of ch must not exceed $255$.
On exit: these values are rearranged into rank order. For example, if ${\mathbf{irank}}\left(i\right)={\mathbf{m1}}$, then the initial value of ${\mathbf{ch}}\left(i\right)$ is moved to ${\mathbf{ch}}\left({\mathbf{m1}}\right)$.
2:     $\mathbf{m1}$ – IntegerInput
3:     $\mathbf{m2}$ – IntegerInput
On entry: the range of the ranks supplied in irank and the elements of ch to be rearranged.
Constraint: $0<{\mathbf{m1}}\le {\mathbf{m2}}$.
4:     $\mathbf{irank}\left({\mathbf{m2}}\right)$ – Integer arrayInput/Output
On entry: elements m1 to m2 of irank must contain a permutation of the integers m1 to m2, which are interpreted as a vector of ranks.
On exit: used as internal workspace prior to being restored and hence is unchanged.
5:     $\mathbf{ifail}$ – IntegerInput/Output
On entry: ifail must be set to $0$, $-1\text{​ or ​}1$. If you are unfamiliar with this argument you should refer to Section 3.4 in How to Use the NAG Library and its Documentation for details.
For environments where it might be inappropriate to halt program execution when an error is detected, the value $-1\text{​ or ​}1$ is recommended. If the output of error messages is undesirable, then the value $1$ is recommended. Otherwise, if you are not familiar with this argument, the recommended value is $0$. When the value $-\mathbf{1}\text{​ or ​}\mathbf{1}$ is used it is essential to test the value of ifail on exit.
On exit: ${\mathbf{ifail}}={\mathbf{0}}$ unless the routine detects an error or a warning has been flagged (see Section 6).

## 6Error Indicators and Warnings

If on entry ${\mathbf{ifail}}=0$ or $-1$, explanatory error messages are output on the current error message unit (as defined by x04aaf).
Errors or warnings detected by the routine:
${\mathbf{ifail}}=1$
 On entry, ${\mathbf{m2}}<1$, or ${\mathbf{m1}}<1$, or ${\mathbf{m1}}>{\mathbf{m2}}$.
${\mathbf{ifail}}=2$
 On entry, the length of each element of ch exceeds $255$.
${\mathbf{ifail}}=3$
Elements m1 to m2 of irank contain a value outside the range m1 to m2.
${\mathbf{ifail}}=4$
Elements m1 to m2 of irank contain a repeated value.
${\mathbf{ifail}}=-99$
See Section 3.9 in How to Use the NAG Library and its Documentation for further information.
${\mathbf{ifail}}=-399$
Your licence key may have expired or may not have been installed correctly.
See Section 3.8 in How to Use the NAG Library and its Documentation for further information.
${\mathbf{ifail}}=-999$
Dynamic memory allocation failed.
See Section 3.7 in How to Use the NAG Library and its Documentation for further information.
If ${\mathbf{ifail}}={\mathbf{3}}$ or ${\mathbf{4}}$, elements m1 to m2 of irank do not contain a permutation of the integers m1 to m2. On exit, the contents of ch may be corrupted. To check the validity of irank without the risk of corrupting ch, use m01zbf.

Not applicable.

## 8Parallelism and Performance

m01ecf is not threaded in any implementation.

The average time taken by the routine is approximately proportional to $n$, where $n={\mathbf{m2}}-{\mathbf{m1}}+1$.

## 10Example

This example reads a file of $12$-character records, each of which contains in characters $1$ to $6$ a name of a NAG routine, and in characters $7$ to $12$ an integer frequency. The program first calls m01dbf to rank the integers in descending order, and then calls m01ecf to rearrange the names into the order specified by the ranks.

### 10.1Program Text

Program Text (m01ecfe.f90)

### 10.2Program Data

Program Data (m01ecfe.d)

### 10.3Program Results

Program Results (m01ecfe.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017