Monolith-0 has asked for the wisdom of the Perl Monks concerning the following question:

I want to get the sorted order of a list of values, but not change the original list. I have an index array in which I wish keep track of the values' sorted order.

For example... start with: 

@stuff_list = ( 'b','t','e','s','u','i' );
@list_order = (  0 , 1 , 2 , 3 , 4 , 5  );

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then sort and get: 
@stuff_list = ( 'b','t','e','s','u','i' );
@list_order = (  0 , 2 , 5 , 3 , 1 , 4  );

[download]
And then use @list_order to access the actual values.

Originally posted as a Categorized Question.

Replies are listed 'Best First'.
Re: How do I sort into an index?
by Monolith-0 (Beadle) on Feb 24, 2001 at 05:41 UTC 
    @list_order = sort { $stuff_list[$a] cmp $stuff_list[$b] } 0 .. $#stuf
+f_list;

    [download]
    Then you can do stuff like the following to see the results: 
    for my $i ( 0 .. $#list_order ) {
    print "$stuff_list[$list_order[$i]]\n";
}

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    or 
    print join( "\n", @stuff_list[@list_order] ), "\n";

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Re: How do I sort into an index?
by tye (Sage) on Feb 23, 2001 at 11:20 UTC
[reply]
[d/l]
Re: How do I sort into an index?
by Soul Singin' (Initiate) on Sep 13, 2010 at 07:36 UTC 
          Original Array:   14  11  10  13  11
       New Positions:    4   1   0   3   2

       Ordered Array:   10  11  11  13  14
  Original Positions:    2   1   4   3   0

    [download]

    Here's the inelegant code I used to do it: 

    #!/usr/bin/env perl

## script to practice creating numeric orderings

use strict ;
use warnings ;

## we want to find the POSITION of each value after ordering
my @values = ( 14 , 11 , 10 , 13 , 11 ) ; 

## now let's do some ordering!
my %orderings = order( @values ) ;

## 
## print original array and positions after ordering

print "\n      Original Array: " ; 
foreach my $value ( @values ) {
    print sprintf( "% 4d" , $value ) ; 
}

print "\n       New Positions: " ; 
foreach my $ordering ( @{ $orderings{ "new_pos" } } ) {
    print sprintf( "% 4d" , $ordering ) ; 
}
print "\n" ; 

## 
## print ordered array and original positions 

print "\n       Ordered Array: " ; 
foreach my $ordering ( @{ $orderings{ "orig_pos" } } ) {
    print sprintf( "% 4d" , $values[ $ordering ] ) ; 
}

print "\n  Original Positions: " ; 
foreach my $ordering ( @{ $orderings{ "orig_pos" } } ) {
    print sprintf( "% 4d" , $ordering ) ; 
}
print "\n\n" ; 


##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  
  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  
##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  

sub order {
    my @inarray = @_ ; 

    ## elements of @inarray MUST be numeric
    foreach my $inval (@inarray) {
    if ( ! is_float( $inval ) ) {
        die "Fatal error. All elements of the \"order\" subroutine mus
+t be numeric." ; 
    }
    }
    my @sorted = sort { $a <=> $b } @inarray ;

    ## make backups 
    my @inarray_bkp = @inarray ; 
    my @sorted_bkp  = @sorted ; 

    ## now get original and new positions -- store in hash of arrays 
    my %orderings ; 

    ## get the original positions 
    for my $i (0..$#sorted) {
    for my $j (0..$#inarray) {

        if ( $sorted[$i] eq $inarray[$j] ) {
        
        ## return the original position
        push( @{ $orderings{ "orig_pos" } } , $j ) ;
        
        ## disqualify as future candidates
        $sorted[$i]  = "AA" ; 
        $inarray[$j] = "ZZ" ; 
        }
    }
    }

    ## restore from backups 
    @inarray = @inarray_bkp ; 
    @sorted  = @sorted_bkp ; 

    ## get the new positions 
    for my $i (0..$#inarray) {
    for my $j (0..$#sorted) {

        if ( $inarray[$i] eq $sorted[$j] ) {
        
        ## return the new position
        push( @{ $orderings{ "new_pos" } } , $j ) ;

        ## disqualify as future candidates
        $inarray[$i] = "AA" ; 
        $sorted[$j]  = "ZZ" ; 
        }
    }
    }

    ## return the original and new positions
    return %orderings ; 
}


sub is_float {
    my $inval = $_[0] ; 
    defined $inval && $inval =~ /^[+-]?\d+(\.\d+)?$/;
}

    [download]

    Originally posted as a Categorized Answer.

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Re: How do I sort into an index?
by Soul Singin' (Initiate) on Sep 14, 2010 at 02:26 UTC

    Here's the elegant solution I was looking for! The following results: 

          Original Array:   14  11  10  13  11
       New Positions:    4   1   0   3   2

       Ordered Array:   10  11  11  13  14
  Original Positions:    2   1   4   3   0

    [download]

    Can be obtained from: 

    #!/usr/bin/env perl

## script to practice creating numeric orderings

use strict ;
use warnings ;

## we want to find the POSITION of each value before and after orderin
+g
my @values = ( 14 , 11 , 10 , 13 , 11 ) ; 

## now let's do some ordering!
my %orderings = order( @values ) ;

## 
## print original array and positions after ordering

print "\n      Original Array: " ; 
foreach my $value ( @values ) {
    print sprintf( "% 4d" , $value ) ; 
}

print "\n       New Positions: " ; 
foreach my $ordering ( @{ $orderings{ "new_pos" } } ) {
    print sprintf( "% 4d" , $ordering ) ; 
}
print "\n" ; 

## 
## print ordered array and original positions 

print "\n       Ordered Array: " ; 
foreach my $ordering ( @{ $orderings{ "orig_pos" } } ) {
    print sprintf( "% 4d" , $values[ $ordering ] ) ; 
}

print "\n  Original Positions: " ; 
foreach my $ordering ( @{ $orderings{ "orig_pos" } } ) {
    print sprintf( "% 4d" , $ordering ) ; 
}
print "\n\n" ;


##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  
  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  
##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  ##  

sub order {
    my @inarray = @_ ; 

    ## elements of @inarray MUST be numeric
    foreach my $inval (@inarray) {
    if ( ! is_float( $inval ) ) {
        die "Fatal error. All elements of the \"order\" subroutine mus
+t be numeric." ; 
    }
    }

    ## get the original positions 
    my %pos_orig ; 
    for my $i (0..$#inarray) {
    push( @{ $pos_orig{ $inarray[$i] }} , $i ) ;
    }

    ## put original positions into an array
    my @orig ; 
    foreach my $key ( sort { $a <=> $b } keys %pos_orig ) {
    push( @orig , @{ $pos_orig{ $key }} ) ; 
    }

    
    ## get the new positions 
    my @sorted = sort { $a <=> $b } @inarray ; 
    my %pos_new ; 
    for my $i (0..$#sorted) {
    push( @{ $pos_new{ $sorted[$i] }} , $i ) ;
    }
    
    ## put new positions into an array
    my @new ; 
    foreach my $key ( @inarray ) {
    push( @new , shift( @{ $pos_new{ $key }} )) ; 
    }

    ## return the original and positions -- as hash of arrays
    my %orderings ; 
    @{ $orderings{ "orig_pos" }} = @orig ; 
    @{ $orderings{ "new_pos"  }} = @new ; 

    return %orderings ; 
}


sub is_float {
    my $inval = $_[0] ; 
    defined $inval && $inval =~ /^[+-]?\d+(\.\d+)?$/;
}

    [download]

    Originally posted as a Categorized Answer.

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Re: How do I sort into an index?
by 2501 (Pilgrim) on Feb 23, 2001 at 18:12 UTC
    use a hash where the key is your sort order and the value is what you would have put in your "value array".

    Originally posted as a Categorized Answer.

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