re-initializing awk array created by split - arrays

Question

I'm trying to use split to reverse the order of characters in a string that appears as the second field in a file with many such lines. The command:
{
n=split($2,arr," ");
for(i=1;i<=n;i++)
s=arr[i] s
}
{ print s }
does this for one line. However, the arr array (and n) seem immortal, so that when I embed this code into an awk script to process multiple lines, the output corresponding to the field I want reversed accumulates (and reverses) all previous lines:
1_B.pdb
GGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRG
AARS_0001_B.pdb
GGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRGGGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRG
AARS_0002_B.pdb
GLILYDGFLDKRDLEGLKYNDILNRTKDVTDVGNTTRTECPDVNRKGGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRGGGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRG
AARS_0003_B.pdb
DGCSLDGFTDDRDLKGALYNKILNKTLIVTDVGNTTRTEVCEKDRYGLILYDGFLDKRDLEGLKYNDILNRTKDVTDVGNTTRTECPDVNRKGGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRGGGTGYPGLKDKDDNEGTKYNKLLNATLIVTDVGNTIRTECPDVNRG
This appears to me to be a problem with re-initialization. I've tried to delete all previous elements of arr[] and to reset n to 0, without any effect. What do I need to do?

Answer 1

It's not arr that's immortal, it's s since you never [re-]init it to "" outside of the loop. arr is getting re-inited on every call to split().
Try this:
{
n=split($2,arr,/ /)
s=""
for(i=1;i<=n;i++)
s=arr[i] s
print s
}
The 3rd arg for split(), by the way is a field separator, not a string, and a field separator is a regexp with a couple of extra properties so the correct way to call split with a fixed "string" is using RE delimiters split($2,arr,/ /), not string delimiters split($2,arr," "). It doesn't make a functional difference in this case but it does when the field separator gets more complicated so best to get used to doing it the right way.
Bonus round: you would not need to explicitly re-init s if you put that code in a function:
function rev(str, arr,n,s,i) {
n=split(str,arr,/ /)
for(i=1;i<=n;i++)
s=arr[i] s
return s
}
...
{ print rev($2) }
Reason left as an exercise :-).