How to parse an array into multiple arrays in BASH

Question

I have an indexed array called wlist[] which contains bunch of words and i want to parse them into multiple arrays such that every new array will consist of words which have same lenght. I keep getting syntax errors from wcholder$i+=("${wlist[$counter]}")

i tried also to change wcholder$i+=("${wlist[$counter]}") with var=wlist[$counter] eval wcholder$i+=("${!var}")

Code:

#!/bin/bash
.
.
.
# mlength=length of the longest word in wlist[]
# wlength=contains length of every word in the same order in wlist[]
for ((i=1; i<=mlength; ++i))
do
   declare -a wcholder$i
done

counter=1
   for i in "${wlength[@]}"; do
   eval wcholder$i+=("${wlist[$counter]}")
   ((counter+=1))
done

It can be done, but in practice "numbered variable names" are quite annoying to work with and usually indicate that you're trying to do something for which shell is the wrong tool. Is there a particular reason you need to do this? — glenn jackman
– glenn jackman, Commented Oct 14, 2020 at 20:33
bash doesn't give you much in the way of data structures. You get "scalars", one-dimensional numerically-indexed arrays, and one-dimensional associative arrays. There are also the positional parameters which act more or less like an array. — glenn jackman
– glenn jackman, Commented Oct 14, 2020 at 21:40
assuming you're looking for anagrams of single words, what benefit do you see from first sorting the words by length? how were you planning on using your arrays in your anagram processing? (re: glenn's 'XY Problem' reference - wondering if it might be of benefit to step back and look at the bigger picture, ie, anagram processing) — markp-fuso
– markp-fuso, Commented Oct 14, 2020 at 21:45
upvoting this even if it is an XY Problem. A worthy attempt at working with anagrams. But shell is not the right tool for this. Shells are good at running jobs and messing with files (even the logic there-of), but data logic should be left to awk, perl, python (maybe c, depending on your goals). I recommend researching awk anagrams (there must be some out there). Also a good Awk tutorial , but there are new concepts to grasp there. Good luck. — shellter
– shellter, Commented Oct 15, 2020 at 3:40

Shawn · Accepted Answer · 2020-10-15 04:24:31Z

1

You can emulate a multi-dimensional array in bash the same way you can in awk: Using an associate array with keys built out of the indexes of the different levels - in case of the following example, length,index. The first word of length 3 is stored in an associate array with the key 3,0, the second 3,1, and so on. The maximum index of each length is stored in a separate array.

#!/usr/bin/env bash

declare -a wordlist=(cat rate bat late rat mate other words) positions
declare -A wordsbylen

for word in "${wordlist[@]}"; do
    len=${#word}
    pos=${positions[$len]:-0}
    wordsbylen[$len,$pos]=$word
    positions[$len]=$((pos+1))
done

for len in "${!positions[@]}"; do
    printf "Words of length %d: " "$len"
    for ((pos=0; pos < ${positions[$len]}; pos++)); do
        printf "%s " "${wordsbylen[$len,$pos]}"
    done
    printf "\n"
done

Running this outputs:

Words of length 3: cat bat rat
Words of length 4: rate late mate
Words of length 5: other words

I agree with the commenters who suggest using a different language with better support for complex data structures, though - the code will end up being much simpler and easier to understand.

edited Oct 15, 2020 at 4:24

answered Oct 15, 2020 at 4:17

Shawn

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Shawn Over a year ago

You could also just build up an array where each element is a string of space-separated words of that index's length, and turn them into arrays when needed, but the above is more robust in that it will work with, say, phrases instead of just single words.

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