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calculating the difference in value between data

Posted on 2009-07-12
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Last Modified: 2012-05-07
Step three in this code calculates the difference between the one value and the next.

the results shown :
232      356      434      767      786      854      avg 571.50      group 0011100210
232      124      78      333      19      68      avg 142.33      

the second line is the difference between the numbers on the first line.

The first entry on the second line reads 232. This should read 0, as we dont need the value from the start here.
Could the code be altered to reflect this ?


#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use List::Util qw(sum);
 
##### Open files
open(my $IN,"invim2.vim") or die "Could not open input: $!\n";
open(my $OUT,">outvim2.vim") or die "Could not open output: $!\n";
 
my @avgs1;
my @avgs2;
my ($maxavg1, $minavg1, $maxavg2, $minavg2);
 
##### Step 1: read a line, and split it on comma
while(<$IN>){
        chomp;
        my @arr = split /,/;
        next unless @arr;
 
 
        # discard 1st and 2nd last and last item
        shift @arr; 
	pop @arr;
	pop @arr;
	# pop @arr;
 
 
        ##### Step 2: Sort data into ascending order
        @arr = sort {$a <=> $b} @arr;
        print "arr @arr\n";
 
 
        ##### Step 3: Calculate difference between neighboring pairs
        my @diff = ($arr[0], map {$arr[$_] - $arr[$_-1]} (1..$#arr));
        print "diff @diff\n";
 
 
        ##### Step 4: Calculate amount in each group
        my @groups = (0)x10;
        foreach my $a (@arr) {
                $groups[$a/100]++;
        }
        print "group @groups\n";
 
 
        ##### Step 5: Calculate average
 
        my $avg1 = sum(@arr)/@arr;
        printf "arr avg %.2f\n", $avg1;
        if(!$maxavg1 || $avg1 > $maxavg1) { $maxavg1 = $avg1; }
        if(!$minavg1 || $avg1 < $minavg1) { $minavg1 = $avg1; }
        push @avgs1, $avg1;
 
        my $avg2 = sum(@diff)/@diff;
        printf "diff avg %.2f\n", $avg2;%.2f
        if(!$maxavg2 || $avg2 > $maxavg2) { $maxavg2 = $avg2; }
        if(!$minavg2 || $avg2 < $minavg2) { $minavg2 = $avg2; }
        push @avgs2, $avg2;
 
        ##### Step 6: Print results
	
	
 
 
        print $OUT join("\t", @arr) . "\tavg " . sprintf("%.2f\t", $avg1) . "group " . join("", @groups) . "\n";
        print $OUT join("\t", @diff) . "\tavg " . sprintf("%.2f\t", $avg2) . "\n";
        print $OUT "\n";
}
 
 
	printf "input: maxavg %d minavg %d avgavg %d\n", $maxavg1, $minavg1, sum(@avgs1)/@avgs1;
	printf $OUT "For data values:\t\t avg avg %.2f\t maximum avg %.2f\t minimum avg %.2f \n", sum(@avgs1)/@avgs1, $maxavg1, $minavg1 ;
	printf "diff: maxavg %d minavg %d avgavg %d\n", $maxavg2, $minavg2, sum(@avgs2)/@avgs2;
	printf $OUT "For data difference values:\t avg avg %.2f\t maximum avg %.2f\t minimum avg %.2f \n", sum(@avgs2)/@avgs2, $maxavg2, $minavg2, ;
 
	
 
close($IN);
close($OUT);

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Question by:MichaelGlancy
  • 11
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  • 4
22 Comments
 
LVL 84

Expert Comment

by:ozo
ID: 24835788
       my @diff = (0, map {$arr[$_] - $arr[$_-1]} (1..$#arr));
But do you want a 0 there, or should there be no value there?
        my @diff =  map {$arr[$_] - $arr[$_-1]} (1..$#arr);
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Expert Comment

by:mrjoltcola
ID: 24835794
Hi Michael, looks like the program got corrupted in your cut and paste. I'll modify from my local copy from last night.
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Expert Comment

by:mrjoltcola
ID: 24835798

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use List::Util qw(sum);
 
##### Open files
open(my $IN,"invim2.vim") or die "Could not open input: $!\n";
open(my $OUT,">outvim2.vim") or die "Could not open output: $!\n";
 
my @avgs1;
my @avgs2;
my ($maxavg1, $minavg1, $maxavg2, $minavg2);
 
##### Step 1: read a line, and split it on comma
while(<$IN>){
        chomp;
        my @arr = split /,/;
        next unless @arr;
 
        # discard 1st and last item
        shift @arr; pop @arr;
 
        ##### Step 2: Sort data into ascending order
        @arr = sort {$a <=> $b} @arr;
        print "arr @arr\n";
 
        ##### Step 3: Calculate difference between neighboring pairs
        my @diff = (0, map {$arr[$_] - $arr[$_-1]} (1..$#arr));
        print "diff @diff\n";
 
        ##### Step 4: Calculate amount in each group
        my @groups = (0)x5;
        foreach my $a (@arr) {
                $groups[$a/10]++;
        }
        print "group @groups\n";
        ##### Step 6: Calculate average
 
        my $avg1 = sum(@arr)/@arr;
        printf "arr avg %.2f\n", $avg1;
        if(!$maxavg1 || $avg1 > $maxavg1) { $maxavg1 = $avg1; }
        if(!$minavg1 || $avg1 < $minavg1) { $minavg1 = $avg1; }
        push @avgs1, $avg1;
 
        my $avg2 = sum(@diff)/@diff;
        printf "diff avg %.2f\n", $avg2;
        if(!$maxavg2 || $avg2 > $maxavg2) { $maxavg2 = $avg2; }
        if(!$minavg2 || $avg2 < $minavg2) { $minavg2 = $avg2; }
        push @avgs2, $avg2;
 
        ##### Step 5: Print results
        print $OUT join("\t", @arr) . "\tavg " . sprintf("%.2f\t", $avg1) . "group " . join("", @groups) . "\n";
        print $OUT join("\t", @diff) . "\tavg " . sprintf("%.2f\t", $avg2) . "\n";
        print $OUT "\n";
}
 
printf "input: maxavg %d minavg %d avgavg %d\n", $maxavg1, $minavg1, sum(@avgs1)/@avgs1;
printf $OUT "maxavg %d minavg %d avgavg %d\n", $maxavg1, $minavg1, sum(@avgs1)/@avgs1;
printf "diff: maxavg %d minavg %d avgavg %d\n", $maxavg2, $minavg2, sum(@avgs2)/@avgs2;
printf $OUT "maxavg %d minavg %d avgavg %d\n", $maxavg2, $minavg2, sum(@avgs2)/@avgs2;
 
close($IN);
close($OUT);

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Author Comment

by:MichaelGlancy
ID: 24835811
hi mrjoltcola,

it want corrupted, I had altered some parts today

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Author Comment

by:MichaelGlancy
ID: 24835822
at step 3,

instead of finding the first value difference (232 in the above example)

the first value difference should not be there
0
 

Author Comment

by:MichaelGlancy
ID: 24835834
maybe it has been corrupted, cant get it to work now
0
 
LVL 40

Expert Comment

by:mrjoltcola
ID: 24835838
I got syntax errors without any mods to your code.

Number found where operator expected at t.pl line 56, near "%.2"
        (Missing operator before 2?)
Bareword found where operator expected at t.pl line 56, near "2f"
        (Missing operator before f?)
syntax error at t.pl line 56, near "%.2"
syntax error at t.pl line 69, near "}"
Execution of t.pl aborted due to compilation errors.
0
 

Author Comment

by:MichaelGlancy
ID: 24835841
now Im lost again. What are mods ?
0
 
LVL 40

Accepted Solution

by:
mrjoltcola earned 500 total points
ID: 24835845
I'm a little confused because on the previous mod I made to this it was to add the 1st value in the diff array, now you want it removed.

Here you go.

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
use List::Util qw(sum);
 
##### Open files
open(my $IN,"invim2.vim") or die "Could not open input: $!\n";
open(my $OUT,">outvim2.vim") or die "Could not open output: $!\n";
 
my @avgs1;
my @avgs2;
my ($maxavg1, $minavg1, $maxavg2, $minavg2);
 
##### Step 1: read a line, and split it on comma
while(<$IN>){
        chomp;
        my @arr = split /,/;
        next unless @arr;
 
 
        # discard 1st and 2nd last and last item
        shift @arr;
        pop @arr;
        pop @arr;
        # pop @arr;
 
 
        ##### Step 2: Sort data into ascending order
        @arr = sort {$a <=> $b} @arr;
        print "arr @arr\n";
 
 
        ##### Step 3: Calculate difference between neighboring pairs
        my @diff = (map {$arr[$_] - $arr[$_-1]} (1..$#arr));
        print "diff @diff\n";
 
 
        ##### Step 4: Calculate amount in each group
        my @groups = (0)x10;
        foreach my $a (@arr) {
                $groups[$a/100]++;
        }
        print "group @groups\n";
 
 
        ##### Step 5: Calculate average
 
        my $avg1 = sum(@arr)/@arr;
        printf "arr avg %.2f\n", $avg1;
        if(!$maxavg1 || $avg1 > $maxavg1) { $maxavg1 = $avg1; }
        if(!$minavg1 || $avg1 < $minavg1) { $minavg1 = $avg1; }
        push @avgs1, $avg1;
 
        my $avg2 = sum(@diff)/@diff;
        printf "diff avg %.2f\n", $avg2;
        if(!$maxavg2 || $avg2 > $maxavg2) { $maxavg2 = $avg2; }
        if(!$minavg2 || $avg2 < $minavg2) { $minavg2 = $avg2; }
        push @avgs2, $avg2;
 
        ##### Step 6: Print results
 
 
 
 
        print $OUT join("\t", @arr) . "\tavg " . sprintf("%.2f\t", $avg1) . "group " . join("", @groups) . "\n";
        print $OUT join("\t", @diff) . "\tavg " . sprintf("%.2f\t", $avg2) . "\n";
        print $OUT "\n";
}
 
 
        printf "input: maxavg %d minavg %d avgavg %d\n", $maxavg1, $minavg1, sum(@avgs1)/@avgs1;
        printf $OUT "For data values:\t\t avg avg %.2f\t maximum avg %.2f\t minimum avg %.2f \n",
                        sum(@avgs1)/@avgs1, $maxavg1, $minavg1 ;
        printf "diff: maxavg %d minavg %d avgavg %d\n", $maxavg2, $minavg2, sum(@avgs2)/@avgs2;
        printf $OUT "For data difference values:\t avg avg %.2f\t maximum avg %.2f\t minimum avg %.2f \n",
                        sum(@avgs2)/@avgs2, $maxavg2, $minavg2, ;
 
 
 
close($IN);
close($OUT);

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Author Comment

by:MichaelGlancy
ID: 24835849
yes, you are right. Thank you. dont be confused, we did want it added, but have realised since that it affects the average in a false way, we didnt see that yesterday

thankyou
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Author Closing Comment

by:MichaelGlancy
ID: 31602623
thank you :)
0
 
LVL 40

Expert Comment

by:mrjoltcola
ID: 24835862
I only changed one line (besides reformatting a couple of lines that were too long into shorter lines)


Original:

my @diff = (0, map {$arr[$_] - $arr[$_-1]} (1..$#arr));

Changed:

my @diff = (map {$arr[$_] - $arr[$_-1]} (1..$#arr));


Actually also what ozo suggested above.
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Author Comment

by:MichaelGlancy
ID: 24835871
if you were to right this in English, what would you be saying ?


my @diff = (0, map {$arr[$_] - $arr[$_-1]} (1..$#arr));
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Expert Comment

by:mrjoltcola
ID: 24835882
diff list equals new list (0) plus list (for each number "i" in arr list from 1 to end, subtract value of number in "i - 1")
0
 
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Expert Comment

by:ozo
ID: 24835893
my @diff = (map {$arr[$_] - $arr[$_-1]} (1..$#arr));
is what I said
0
 

Author Comment

by:MichaelGlancy
ID: 24835897
sorry ozo, I didnt understand what you did. I copied it into my script and couldnt get it to work for me.
0
 

Author Comment

by:MichaelGlancy
ID: 24835901
Im a complete beginner at this. I am scraping my way through with the help of you guys
0
 
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Expert Comment

by:mrjoltcola
ID: 24835917
The difference in what ozo said:

(map {$arr[$_] - $arr[$_-1]} (1..$#arr));

and:

(0, map {$arr[$_] - $arr[$_-1]} (1..$#arr));


Is just the 1st element in the list. In Perl you can create list expressions out of other elements or lists by just listing comma delimited as:

(0, 1, 2, ...)
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Author Comment

by:MichaelGlancy
ID: 24835920
should  I reassign points ?
0
 
LVL 84

Expert Comment

by:ozo
ID: 24835987
How did you copy it it into your script, and in what way did it not work?
0
 
LVL 84

Expert Comment

by:ozo
ID: 24835992
see
 List value constructors
in
perldoc perldata
0
 

Author Comment

by:MichaelGlancy
ID: 24835998
well I just copied it over, and as the program ran, the command prompt window just flashed past and there was no creation of the output file. At tha point I just went with mrjolt's code

I dont really know enough to say at this point. I really am learning this as I go along. Your code was fine, it is my inability that is the problem . .. .
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