n-th column are same? (q14277104369)

#!/bin/bash
set -euo pipefail
file=${1:-./list.txt}
col=$(cat -- "$file" | head -1 | awk -F, '$0=NF')
f=$(mktemp)
trap 'rm -f "$f"' EXIT
for ((i = 1; i <= col; ++i)); do
  cat -- "$file" | cut -d, -f$i | sort -t, -u >"$f"
  if (($(wc -l <"$f") > 1)); then continue; fi
  # do something
  n=$(grep -Po '\d+' <"$f")
  echo $i "$n"
done