计算距离； 使用awk从第一行的第二列减去第二行的第一列

Question

I have a question. I have a file with coordinates ( TAB separated)

2 10
35 50
90 200
400 10000
...

I would like to substract the first column of the second line from the second column of the fist line , ie calculate the distance, ie I would like a file with

25
40
200
...

How could I do that using awk??? Thank you very much in advance

Answer 1

here is an awk one-liner may help you:

kent$  awk 'a{print $1-a}{a=$2}'  file
25
40
200

Answer 2

Here's a pure bash solution:

{
    read _ ps
    while read f s; do
        echo $((f-ps))
        ((ps=s))
    done
} < input_file

This only works if you have (small) integers, as it uses bash's arithmetic. If you want to deal with arbitrary sized integers or floats, you can use bc (with only one fork):

{
    read _ ps
    while read f s; do
        printf '%s-%s\n' "$f" "$ps"
        ps=$s
    done
} < input_file | bc

Now I leave the others give an awk answer!

---

Alright, since nobody wants to upvote my answer, here's a really funny solution that uses bash and bc :

a=( $(<input_file) )
printf -- '-(%s)+(%s);\n' "${a[@]:1:${#a[@]}-2}" | bc

or the same with dc (shorter but doesn't work with negative numbers):

a=( $(<input_file) )
printf '%s %sr-pc' "${a[@]:1:${#a[@]}-2}" | dc

Answer 3

using sed and ksh for evaluation

sed -n "
1x
1!H
$ !b

x
s/^ *[0-9]\{1,\} \(.*\) [0-9]\{1,\} *\n* *$/\1 /
s/\([0-9]\{1,\}\)\(\n\)\([0-9]\{1,\}\) /echo \$((\3 - \1))\2/g
s/\n *$//
w /tmp/Evaluate.me
"
. /tmp/Evaluate.me
rm /tmp/Evaluate.me