#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11132653
use warnings;
#use File::Basename;

my ($nameA, $nameB) = qw( data.A data.B ); # FIXME just for testing

## filename
#my ($nameA,$pathA,$suffixA) = fileparse($ARGV[0],'\.[^\.]*');
#my ($nameB,$pathB,$suffixB) = fileparse($ARGV[1],'\.[^\.]*');
my $nameC = $nameA =~ s/\.\K.*/dif/r;

# read data
open(dataA, $nameA)   or die " cannot open/read file $nameA:$!\n";
my @headerA; push @headerA, $_ = <dataA> for 1 .. 2;
my @multi_arrayA; push @multi_arrayA, [split(' ', $_)] for <dataA>;
#pop @multi_arrayA; pop @multi_arrayA; # trash header
close dataA;
open(dataB, $nameB)   or die " cannot open/read file $nameB:$!\n";
my @headerB; push @headerB, $_ = <dataB> for 1 .. 2;
my @multi_arrayB; push @multi_arrayB, [split(' ', $_)] for <dataB>;
#pop @multi_arrayB; pop @multi_arrayB; # trash header
close dataB;

# modify data
my @multi_arrayC;
my ($avgX,$avgY,$avgZ,$difF); #u_cor_T pi_T_ts TFP eta_is_T_ts
for my $i (0..$#multi_arrayA) {

    $avgX = ( $multi_arrayA[$i]->[0] + $multi_arrayB[$i]->[0] ) / 2.;
    $avgY = ( $multi_arrayA[$i]->[1] + $multi_arrayB[$i]->[1] ) / 2.;
    $avgZ = ( $multi_arrayA[$i]->[2] + $multi_arrayB[$i]->[2] ) / 2.;
    $difF = $multi_arrayA[$i]->[3] - $multi_arrayB[$i]->[3];

#    push( $multi_arrayC[$i]->[0], $avgX );
#    push( $multi_arrayC[$i]->[1], $avgY );
#    push( $multi_arrayC[$i]->[2], $avgZ );
#    push( $multi_arrayC[$i]->[3], $difF );

    $multi_arrayC[$i]->[0] = $avgX;
    $multi_arrayC[$i]->[1] = $avgY;
    $multi_arrayC[$i]->[2] = $avgZ;
    $multi_arrayC[$i]->[3] = $difF;

}

use Data::Dump 'dd'; dd \@multi_arrayA, \@multi_arrayB, $nameC, \@mult
+i_arrayC;

# write data
open(dataC, ">". $nameC)   or die " cannot open/read file $nameC:$!\n"
+;
print dataC join(" ", map { sprintf "%E", $_ } @$_),"\n" for @multi_ar
+rayC;
close dataC;

system "echo following is output file $nameC; cat $nameC"; # FIXME tes
+ting

## input
#__dataA__
#variables
#units
#1.0 1.0 1.0 4.0 9.99999
#2.0 2.0 2.0 4.0 9.99999
#3.0 3.0 3.0 4.0 9.99999
#
#__dataB__
#variables
#units
#3.0 3.0 3.0 5.0 9.99999
#2.0 2.0 2.0 5.0 9.99999
#1.0 1.0 1.0 5.0 9.99999
#
## output (expected
#__dataC__
#variables
#units
#2.00000E0 2.00000E0 2.00000E0 1.00000E0
#2.00000E0 2.00000E0 2.00000E0 1.00000E0
#2.00000E0 2.00000E0 2.00000E0 1.00000E0
[download]

Outputs:

(
  [
    ["1.0", "1.0", "1.0", "4.0", 9.99999],
    ["2.0", "2.0", "2.0", "4.0", 9.99999],
    ["3.0", "3.0", "3.0", "4.0", 9.99999],
  ],
  [
    ["3.0", "3.0", "3.0", "5.0", 9.99999],
    ["2.0", "2.0", "2.0", "5.0", 9.99999],
    ["1.0", "1.0", "1.0", "5.0", 9.99999],
  ],
  "data.dif",
  [[2, 2, 2, -1], [2, 2, 2, -1], [2, 2, 2, -1]],
)
following is output file data.dif
2.000000E+00 2.000000E+00 2.000000E+00 -1.000000E+00
2.000000E+00 2.000000E+00 2.000000E+00 -1.000000E+00
2.000000E+00 2.000000E+00 2.000000E+00 -1.000000E+00
[download]

I confirm this code works fine. This wisdom will be used in all derivatives of that code. I also see the advantages of using Data::Dump and noted #FIXME comments highlighting. Thank you very much! Any ideas how to trap an empty line at the end of a data file which it may have?

replace

my @multi_arrayA; push @multi_arrayA, [split(' ', $_)] for <dataA>;
[download]

with:

my @multi_arrayA; push @multi_arrayA, [split(' ', $_)] for grep /\S/, 
+<dataA>;
[download]

in both places, changing A to B in the second one, of course.

# copy headers to output
my $headerA = <$dataA> . <$dataA>;
my $headerB = <$dataB> . <$dataB>;
print $dataC "__dataC__\n$headerA";

while (1) {
    last if (eof($dataA) or eof($dataB));
    my @A = (split( /\s+/, <$dataA>))[0..3];
    my @B = (split( /\s+/, <$dataB>))[0..3];
    my $avgX = ($A[0] + $B[0])/2;
    my $avgY = ($A[1] + $B[1])/2;
    my $avgZ = ($A[2] + $B[2])/2;
    my $difF = ($A[3] - $B[3]);
    printf $dataC "%E %E %E %E\n", $avgX, $avgY, $avgZ, $difF;
}
[download]

I recommend three things:

1. Fix your compilation errors
2. Fix your runtime errors
3. Fix your logic errors

I could give more specific help if you would give a more specific problem statement than "I do not seem to accomplish that."

When I try to run your code under Perl 5.32.1 I get

Experimental push on scalar is now forbidden at fubar.new line 32, nea
+r "$avgX )"
Experimental push on scalar is now forbidden at fubar.new line 33, nea
+r "$avgY )"
Experimental push on scalar is now forbidden at fubar.new line 34, nea
+r "$avgZ )"
Experimental push on scalar is now forbidden at fubar.new line 35, nea
+r "$difF )"
Execution of fubar.new aborted due to compilation errors.
[download]

Hi,

Please provide some sample data that you are feeding to your program. See also sprintf?

Thanks. The sample data is under __dataA__ and __dataB__ I am not sure how to best avoid opening files when the data exists. The input format is floats, the output is supposed to be scientific format.

Hi again,

Forgive me but I don't know what "scientific format" is. Please show the expected output from the sample data.

$ perl -Mstrict -wE 'my $avg = (1.10000E0 + 3.10000E0) / 2.; say sprin
+tf("%E", $avg)'
2.100000E+00
[download]

?


The way forward always starts with a minimal test.