zsh on MacOS: how to create an associative array (hash table) from the from two column-like scalars?

Question

I have two scalar values in the form of columns:

% echo $key
hom
doc
fam

echo $val
'home'
'Documents'
'Family'

and I want to create associative array from them.

I'm aware about the method of creation the associative array like below:

declare -A my_assoc_arr
my_assoc_arr=(hom home doc Documents fam Family)

But what is the easiest method create an associative array by digesting $key and $val in the form as I have them (scalar, column-like)? Is there any other association syntax, or I need to put my effort into reshuffling $key and $val to the association syntax above?

Answer 1

You probably need a loop, but it's not too messy. You'll just use two read commands to read a line from each string at one time.

typeset -A arr

while IFS= read -u 3 -r k
      IFS= read -u 4 -r v
do
    arr[$k]=$v
done 3<<< $key 4<<< $val

The first read reads from file descriptor 3 (which is redirected from a here string created from $key , the second from file descriptor 4 (likewise redirected from $val ).

$ typeset -p arr
typeset -A arr=( [doc]=Documents [fam]=Family [hom]=home )

(This assumes key and val have the same number of lines. I don't want to go down the rabbit hole of dealing with the alternative, which makes you decide what to do with leftover keys or values.)

Answer 2

In zsh you can also use the 'zip' operator to reshuffle two standard arrays into the associative array syntax you mentioned:

typeset -a keys=("${(f@)key}") vals=("${(f@)val}")
typeset -A arr=("${(@)keys:^vals}")

Some of the pieces:

• ${f)...} - uses the f parameter expansion flag to split a string on newlines.
• "${(@)...}" - ensures that empty values and values with spaces are handled (probably not absolutely necessary here).
• ${...:^...} - zips two arrays together, alternating values from each array. The resulting array will be twice the length of the shortest input array.
• typeset -A arr=(k1 v1 k2 v2) - creates an associative array from the alternating keys and values.