Bash script to read list of 20+ items into array, then generate all combinations of four items from list

Question

I have a file "ingredients.txt" that has a list of 38 words (one per each line). I have figured out how to read it into an array

getArray() { array=() while IFS= read -r line do array+=("$line") done < "$1" } getArray "ingredients.txt" 

But now how to get output of all combinations of exactly 4 words from the list of 38?

EDIT: To respond to a comment, I do mean combinations and not permutations, and repetitions are not valid. Four unique words in each combination.

To further clarify, think of it as drawing four marbles of 38 different colors from a bag. No two colors alike. Once you draw a red one, it is impossible to draw another red one for that combination. You draw four, write down the colors, and put them back in the bag, and draw another four. If you get {blue, yellow, purple, red} and {yellow, purple, red, blue} they are not counted separately. I just want combinations, not permutations.

Also, I want each combination printed (going back to the ingredients list): onion, cheese, meat, bun lettuce, carrot, celery, radish carrot, lettuce, celery, vinegar etc.

I hope this is clear.

Answer 1

In Python:

import itertools.combinations with open('ingredients.txt') as fd: words= fd.readlines() for combination in itertools.combinations(words, 4): print(combination) 

Answer 2

I tried by using python

>>> a ['praveen', 'ajay', 'abhi', 'chetan', 'abh', 'cat'] for i in range(0,len(a),4): ... print a[i:i+4] ... ['praveen', 'ajay', 'abhi', 'chetan'] ['abh', 'cat'] 

Answer 3

Just for the fun of it, a version in plain bash (which I do not recommend using for long lists, it is quite slow (as should be expected), it takes more than two minutes to do in shell what in c gets done in half a second.):

#!/bin/bash - set -u readarray -t b <ingredients.txt r=${1:-3} n=${2:-5} main(){ combinations } combinations(){ : ${r:=3} ${n:=5} # default values ## The first line of elements is easy, fill an array of r elements: for ((i=0 ; i<r ; i++)); do a[i]=$i done printelements ## Up to the maximum permitted value of the first array element. while (( a[0] < n-r )); do ## search backwards on the array for a value less than maximum. for ((i = r-1; i >= 0; i--)); do ## If an item is below its maximum permitted value... if ((a[i] < n-r+i )); then ## increment it: ((a[i]++)) break fi done ## Fill the rest of the array with consecutive values: for (( i = i + 1 ; i < r ; i++ )); do (( a[i] = a[i-1] + 1 )) done ## Print the current combination of items: printelements done } printelements(){ : #p=${a[@]/%/ }; printf '%s\n' "<${p% }>"; } s="" for i in "${a[@]}"; do printf '%s' "$s" "${b[i]}" s=" " done echo } main 

Running it as:

$ ./script 4 38 

Will print:

$ ./script 4 38 | wc -l 73815 

As math will confirm (fact is a library defined function):

$ bc <<<"r=4;n=38;fact(n)/(fact(r)*fact(n-r))" # n! / ( r! × (n-r)! ) 73815 

Answer 4

Well, try with below code

getArray() { array=() while IFS= read -r line do array+=("$line") done < "$1" for i in ${!array[@]} do if [ ${#array[$i]} == 4 ]; then echo "${array[$i]}" fi done } getArray "ingredients.txt"