I would like to iterate over pairs of elements in bash. In Python, this is straigthforward:
x_list = [1, 2, 3, 4]
y_list = ["a", "b", "c", "d"]
for x, y in zip(x_list , y_list):
# here we have access to the values (i.e. the pairs are assigned to variables):
result = do_something(x, y)
print(result)
How can I replicate such a behavior in bash? I would need to store the values of the pairs into variables inside of the for loop, so that I can perform some operations. It should be something like:
for x, y in 1a 2b 3c 4d
do
python script.py --x_value=${x} --y_value=${y}
done
Note that the elements of the list could be also complicated stuff, such as:
x_list = [1e-5, 1e-4, 1e-3]
and y_list = [10, 20, 30]
CodePudding user response:
A possible translation of your code would be:
#!/bin/bash
list0=(1 2 3 4)
list1=(a b c d)
for i in "${!list0[@]}"
do
x=${list0[i]}
y=${list1[i]}
printf '%q %q\n' "$x" "$y"
done
1 a
2 b
3 c
4 d
But it relies on the fact that the two newly created arrays will have identical indexes. Here's an illustration of the problem:
#!/bin/bash
list0=(1 2 3 4)
list1=(a b c d)
unset list0[0] list1[1]
for i in "${!list0[@]}"
do
x=${list0[i]}
y=${list1[i]}
printf '%q %q\n' "$x" "$y"
done
2 ''
3 c
4 d
CodePudding user response:
Here's an option using associative arrays
x_list=(1 2 3 "1e-5" 999)
y_list=("a" "b" "c" "d")
declare -A arr
max=$(( ${#x_list[@]} - 1 ))
# use the smallest size
echo "Sizes: x_list: ${#x_list[@]} y_list: ${#y_list[@]} max: $max"
if [ "${#x_list[@]}" -gt "${#y_list[@]}" ];then
max=$(( ${#y_list[@]} - 1 ))
fi
for i in $(seq 0 $max);do
arr[${x_list[$i]}]=${y_list[$i]}
echo "${x_list[$i]} -> ${y_list[$i]}; ${arr[${x_list[$i]}]}"
done
Result
Sizes: x_list: 5 y_list: 4 max: 4
1 -> a; a
2 -> b; b
3 -> c; c
1e-5 -> d; d
Iterating over keys
for key in "${!arr[@]}"; do
echo "key=$key, value=${arr[$key]}"
done
Result:
key=1, value=a
key=2, value=b
key=3, value=c
key=1e-5, value=d
CodePudding user response:
If you've got two non-sparse arrays then the code in Fravadona's answer is a good option. If at least one of the arrays is sparse then this Shellcheck-clean code is one way to do it:
#! /bin/bash -p
x_list=([0]=1 [2]=2 [4]=3 [6]=4)
y_list=([1]=a [3]=b [5]=c [7]=d)
for x in "${x_list[@]}"; do
IFS= read -r -d '' y
printf '%q %q\n' "$x" "$y"
done < <(printf '%s\0' "${y_list[@]}")