修改数组中逗号分隔值的最简单方法？

Question

Let's say I have an array of n elements. Each element is a string of comma-separated x,y coordinate pairs, eg "581,284". There is no set character length to these x,y values.

Say I wanted to subtract 8 from each x value, and 5 from each y value.

What would be the simplest way to modify x and y, independently of each other, without permanently splitting the x and y values apart?

eg the first array element "581,284" becomes "573,279", the second array element "1013,562" becomes "1005,274", and so forth.

I worked on this problem for a couple of hours (I'm an amateur at bash), and it seemed as if my approach was awfully convoluted.

Please note that the apostrophes above are only added for emphasis, and are not a part of the problem.

Thank you in advance, I've been racking my head over this for a while now!

Edit: The following excerpt is the approach I was taking. I don't know much about bash, as you can tell.

   while read value
   do
     if [[ -z $offset_list ]]
     then
       offset_list="$value"
     else
       offset_list="$offset_list,$value"
     fi
   done < text.txt
   new_offset=${offset_list//,/ }
   read -a new_array <<< $new_offset

   for value in "${new_array[@]}"
     do
       if [[ $((value%2)) -eq 1 ]]
       then
         value=$((value-8));
         new_array[$counter]=$value
         counter=$((counter+1));
       elif [[ $((value%2)) -eq 0 ]]
       then
         value=$((value-5));
         new_array[$counter]=$value
         counter=$((counter+1));
       fi
     done

Essentially I had originally read the coordinate pairs, and stripped the commas from them, and then planned on modifying odd/even values which were populated into the new array. At this point I realized that there had to be a more efficient way.

Answer 1

I believe the following should achieve what you are looking for:

#!/bin/bash

input=("581,284" "1013,562")

echo "Initial array ${input[@]}"
for index in ${!input[@]}; do
    value=${input[$index]}
    x=${value%%,*}
    y=${value##*,}

    input[$index]="$((x-8)),$((y+5))"
done

echo "Modified array ${input[@]}"

${!input[@]} allows us to loop over the indexes of the bash array.

${value%%,*} and ${value##*,} relies on bash parameter substitution to remove the everything after or before the comma (respectively). This effectively splits your string into two variables.

From there, it's your required math and variable reassignment to mutate the array.