I have an array in Bash, say it contains the numbers {1, 2, 3, 4, 5}. I want to extract some of those numbers randomly, such that the same number doesn't get extracted twice.
Basically, if I wanted to extract 3 numbers from the array, I want results like: {3, 4, 1} or {5, 2, 4} and not {1, 1, 3} or {2, 5, 2}.
I've tried deleting elements as I extract them, but it always seems to mess up. Can anyone help?
Decided to write an answer, as I found the --input-range option to shuf that turned out handy:
N=3
ARRAY=( zero one two three four five )
for index in $(shuf --input-range=0-$(( ${#ARRAY[*]} - 1 )) -n ${N})
do
echo ${ARRAY[$index]}
done
How about this:
for i in {1..10}; do
echo $i
done | shuf
That will return all the numbers. If you only want a specific amount, do this:
numbers=5
for i in {1..10}; do
echo $i
done | shuf | head -$numbers
And if you want to change the numbers, just change the {1..10} variable to whatever you want.
shuf --input-range 1-10 you don't need the for loop to render a set of array indices.Yet another syntax, still using shuf, and preserving elements with spaces:
N=3
ARRAY=( one "two = 2" "3 is three" 4 five )
for el in "${ARRAY[@]}"; do echo $el; done | shuf | head -$N
very simple 'oneliner' i like:
shuf -e ${POOL[@]} -n3
will give you 3 random elements from your $POOL array
ex:
#~ POOL=(a b c d e)
#~ shuf -e ${POOL[@]} -n3
d
e
a
This might work for you, if you want a genuine pure bash solution.
takeNrandom() {
# This function takes n+1 parameters: k a1 a2 ... an
# Where k in 0..n
# This function sets the global variable _takeNrandom_out as an array that
# consists of k elements chosen at random among a1 a2 ... an with no repetition
local k=$1 i
_takeNrandom_out=()
shift
while((k-->0 && $#)); do
((i=RANDOM%$#+1))
_takeNrandom_out+=( "${!i}" )
set -- "${@:1:i-1}" "${@:i+1}"
done
}
Try it:
$ array=( $'a field with\na newline' 'a second field' 'and a third one' 42 )
$ takeNrandom 2 "${array[@]}"
$ declare -p _takeNrandom_out
declare -a _takeNrandom_out='([0]="a second field" [1]="a field with
a newline" [2]="and a third one")'
(the newline is really preserved in the array field).
This uses positional parameters, and uses set -- "${@:1:i-1}" "${@:i+1}" to remove the i-th positional parameter. We also used indirect expansion in the line _takeNrandom_out+=( "${!i}" ) to have access to the i-th positional parameter.
Note. This uses the RANDOM variable with a modulo, so the distribution is not exactly uniform. It should be fine for arrays with a small number of fields. Anyway if you have a huge array, you probably shouldn't be using Bash in the first place!
