Append two columns adding a specific integer at each value in Unix - unix

Question

I have two files like this:
# step distance
0 4.48595407961296e+01
2500 4.50383737781376e+01
5000 4.53506757198727e+01
7500 4.51682465277482e+01
10000 4.53410353656445e+01
# step distance
0 4.58854106214881e+01
2500 4.58639266431320e+01
5000 4.60620560167519e+01
7500 4.58990075106227e+01
10000 4.59371359946124e+01
So I want to join the two files together, while maintaining the spacing.
Especially, the second file needs to remember the ending values of the first one and start counting from that one.
output:
# step distance
0 4.48595407961296e+01
2500 4.50383737781376e+01
5000 4.53506757198727e+01
7500 4.51682465277482e+01
10000 4.53410353656445e+01
12500 4.58854106214881e+01
15000 4.58639266431320e+01
17500 4.60620560167519e+01
20000 4.58990075106227e+01
22500 4.59371359946124e+01
With calc it was easy to do the problem is that the spacing needs to be in order to work and in that case calc makes a complete mess.

Answer 1

# start awk and set the *Step* between file to 2500
awk -v 'Step=2500' '
# 1st line of 1 file (NR count every line, from each file) init and print header
NR == 1 {LastFile = FILENAME; OFS = "\t"; print}
# when file change (new filename compare to previous line read)
# Set a new index (for incremental absolute step from relative one) and new filename reference
FILENAME != LastFile { StartIndex = LastIndex + Step; LastFile = FILENAME}
# after first line and for every line stating witha digit (+ space if any)
# calculate absolute step and replace relative one, print the new content
NR > 1 && /^[[:blank:]]*[0-9]/ { $1 += StartIndex; LastIndex = $1;print }
' YourFiles*
Result will depend of files order
output separator is set by OFS value (tab here)

Answer 2

Perl to the rescue!
#!/usr/bin/perl
use warnings;
use strict;
open my $F1, '<', 'file1' or die $!;
my ($before, $after, $diff);
my $max = 0;
while (<$F1>) {
print;
my ($space1, $num, $space2) = /^(\s*) ([0-9]+) (\s*)/x or next;
($before, $after) = ($space1, $space2);
$diff = $num - $max;
$max = $num;
}
$before = length "$before$max"; # We'll need it to format the computed numbers.
open my $F2, '<', 'file2' or die $!;
<$F2>; # Skip the header.
while (<$F2>) {
my ($step, $distance) = split;
$step += $max + $diff;
printf "% ${before}d%s%s\n", $step, $after, $distance;
}
The program remembers the last number in $max. It also keeps the length of the leading whitespace plus $max in $before to format all future numbers to take up the same space (using printf).
You didn't show how the distance column is aligned, i.e.
20000 4.58990075106227e+01
22500 11.59371359946124e+01 # dot aligned?
22500 11.34572478912301e+01 # left aligned?
The program would align it the latter way. If you want the former, use a similar trick as for the step column.