Subtracting floating point numbers in a loop in bash

Question

I have a file with 500 lines of floating point numbers. What I want to do is take a line, and then subtract every line lower in linenumber from that line. An example nonworking script would be:

for i in `seq 0 499`; do
       for ((j=0; j<i; j++)); do
               a=$(awk 'NR == i' i=$i inputfile)
               b=$(awk 'NR == j' j=$j inputfile)
               echo $(awk '{c=a-b};END{print c/NR}' a=$a b=$b)
       done
done > outputfile

I'm not familiar with how to use awk, so any help would be appreciated. Thank you!

Example:

input:

1
2
3
4
5

output:

1
2 - 1
3 - 1
3 - 2
4 - 1
4 - 2
4 - 3
5 - 1
5 - 2
5 - 3
5 - 4

Except instead of integers everything is a floating point number, and the subtractions should be evaluated

Answer 1

If you put this into a.awk

{
    a[NR] = $1
}
END {
    print a[1]
    for (i = 2; i <= NR; i++) 
        for (j = 1; j < i; j++) 
            print a[i]-a[j]
}

and run

awk -f a.awk foo.txt

You will get your desired output.

For example, if your input was

1.2
2.3
3.4
4.5
5.6

Your output would be

1.2
1.1
2.2
1.1
3.3
2.2
1.1
4.4
3.3
2.2
1.1