If statement for two different arrays in bash - arrays

Question

I have two arrays, which are arrAlpha[] and arrPT[]. Array arrAlpha contains the Alphabets and array arrPT[] contains some of the plain letters.following is the code that i wrote in bash shell script to compare elements of both arrays and to store the position elements of arrPT[] in arrAlpha[] to array arrT[]. But when i run i feel like something is wrong in if statement to print out the elements in arrT[]. can anyone help me please?
#!/bin/bash
arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
arrPT=(E K N R S W )
lenPT=${#arrPT}
declare -A arrT
q=0
for((i=0; i<lenPT; i++)) do
for((j=i; j<26; j++)) do
if [ ${arrPT[$i]} = ${arrAlpha[$j]} ]; then
arrT[$q]=$j % 26;
((++q));
fi
done
done
echo ${arrAlpha[#]}
echo ${arrPT[#]}
echo ${arrT[#]}
the expected output is to change elements arrPT to number 0 to 25.
arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
arrPT =(E K N R S W)
arrT =(4 10 13 17 18 22)

Answer 1

Here's a fixed version of your script - there are some style changes that I prefer
arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
arrPT=(E K N R S W )
# array length needs index *
lenPT=${#arrPT[*]}
# seems arrT can be simple indexed array
declare -a arrT
q=0
for((i=0; i<lenPT; ++i)); do
for((j=0; j<26; ++j)); do
if [[ ${arrPT[i]} == ${arrAlpha[j]} ]]; then
# arithmetic inside $(())
arrT[q++]=$((j % 26))
fi
done
done
echo ${arrAlpha[#]}
echo ${arrPT[#]}
echo ${arrT[#]}

Answer 2

The main bug is with this line:
lenPT=${#arrPT}
which should be written like:
lenPT=${#arrPT[#]}
But, in fact, there is no need (even if it is not wrong to use it) for such variable, change this line:
for((i=0; i<lenPT; i++)) do
to:
for((i=0; i<${#arrPT[#]}; i++)) do
Some other issues:
There is no need to mod 26 the value of $j, it will never reach 26.
The array arrT seems to be an indexed array: -a no need for -A.
There is no need for variable q if each result will be in the same position as the index i
Please quote your expansions.
Use printf (more reliable) instead of echo.
The script with all the above done is:
#!/bin/bash
arrAlpha=(A B C D E F G H I J K L M N O P Q R S T U V W X Y Z)
arrPT=(E K N R S W )
declare -a arrT
for((i=0; i<${#arrPT[#]}; i++)) do
for((j=i; j<${#arrAlpha[#]}; j++)) do
[[ ${arrPT[i]} == "${arrAlpha[j]}" ]] && let arrT[i]=j
done
done
printf '%s ' "${arrAlpha[#]}" ; echo
printf '%3s ' "${arrPT[#]}" ; echo
printf '%3s ' "${arrT[#]}" ; echo
Of course, the second loop could be removed by cutting that string at the character:
#!/bin/bash
Alpha=ABCDEFGHIJKLMNOPQRSTUVWXYZ
arrPT=(E K N R S W )
declare -a arrT
for((i=0; i<${#arrPT[#]}; i++)) do
arrT[i]=${Alpha%"${arrPT[i]}"*} # cut the string at the character.
arrT[i]=${#arrT[i]} # Use the len of the cut string.
done
printf '%s ' "$Alpha" ; echo
printf '%3s ' "${arrPT[#]}" ; echo
printf '%3s ' "${arrT[#]}" ; echo