Removing duplicates on a variable without sorting.

Question

I have a variable that contains the following space separated entries.

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"

How do I remove the duplicates without sorting?

#Something like this.
new_variable="apple lemon papaya avocado grapes mango banana"

I have found somewhere a script that accomplish removing the duplicates of a variable, but does sort the contents.

#Not something like this.
new_variable=$(echo "$variable"|tr " " "\n"|sort|uniq|tr "\n" " ")
echo $new_variable
apple avocado banana grapes lemon mango papaya

Answer 1

new_variable=$( awk 'BEGIN{RS=ORS=" "}!a[$0]++' <<<$variable );

Here's how it works:

RS (Input Record Separator) is set to a white space so that it treats each fruit in $variable as a record instead of a field. The non-sorting unique magic happens with !a[$0]++. Since awk supports associative arrays, it uses the current record ($0) as the key to the array a[]. If that key has not been seen before, a[$0] evaluates to '0' (awk's default value for unset indices) which is then negated to return TRUE. I then exploit the fact that awk will default to 'print $0' if an expression returns TRUE and no '{ commands }' are given. Finally, a[$0] is then incremented such that this key can no longer return TRUE and thus repeat values are never printed. ORS (Output Record Separator) is set to a space as well to mimic the input format.

A less terse version of this command which produces the same output would be the following:

awk 'BEGIN{RS=ORS=" "}{ if (a[$0] == 0){ a[$0] += 1; print $0}}'

Gotta love awk =)

EDIT

If you needed to do this in pure Bash 2.1+, I would suggest this:

#!/bin/bash    

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
temp="$variable"

new_variable="${temp%% *}"

while [[ "$temp" != ${new_variable##* } ]]; do
   temp=${temp//${temp%% *} /}
   new_variable="$new_variable ${temp%% *}"
done

echo $new_variable;

Answer 2

shell

declare -a arr
variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
set -- $variable
count=0
for c in $@
do
    flag=0
    for((i=0;i<=${#arr[@]}-1;i++))
    do
        if [ "${arr[$i]}" == "$c" ] ;then
            flag=1
            break
        fi
    done
    if  [ "$flag" -eq 0 ] ; then
        arr[$count]="$c"
        count=$((count+1))
    fi
done
for((i=0;i<=${#arr[@]}-1;i++))
do
   echo "result: ${arr[$i]}"
done

Result when run:

linux# ./myscript.sh
result: apple
result: lemon
result: papaya
result: avocado
result: grapes
result: mango
result: banana

OR if you want to use gawk

awk 'BEGIN{RS=ORS=" "} (!($0 in a) ){a[$0];print}'

Answer 3

This pipeline version works by preserving the original order:

variable=$(echo "$variable" | tr ' ' '\n' | nl | sort -u -k2 | sort -n | cut -f2-)

Answer 4

Pure Bash:

variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"

declare new_value=''

for item in $variable; do
  if [[ ! $new_value =~ $item ]] ; then   # first time?
    new_value="$new_value $item"
  fi
done
new_value=${new_value:1}                  # remove leading blank

Answer 5

Z Shell:

% variable="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
% print ${(zu)variable}                                                               
apple lemon papaya avocado grapes mango banana

Answer 6

In pure, portable sh:

words="apple lemon papaya avocado lemon grapes papaya apple avocado mango banana"
seen=
for word in $words; do
  case $seen in
    $word\ * | *\ $word | *\ $word\ * | $word) 
      # already seen
      ;;
    *)
      seen="$seen $word"
      ;;
  esac
done
echo $seen