#! /bin/bash
echo '' > idu.txt
for u in $(
  awk -v FS="\t" '
  {
    for (i=2;i<=NF;i++) { printf("%s\n",$i) }
  }
  ' idx.txt | sort | uniq
)
do
  echo "$u" >> idu.txt
  grep "$u" idx.txt | cut -f 1 >> idu.txt
  echo >> idu.txt
done
