#!/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]

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