awk 'bucketise' numerical values

cat <INPUT FILE> | awk '{ bucket = int(($NUM) / <BUCKET SIZE>) * <BUCKET SIZE> ; arr[bucket]++} END { for (i in arr) {print i, arr[i] }}' | sort -g

# e.g.
#
# cat access.log.app025.26072016.txt | awk '{ bucket = int(($6 / 1000000) / 100) * 100 ; arr[bucket]++} END { for (i in arr) {print i, arr[i] }}' | sort -g
# $6 / 1000000 because apache request times are microseconds by default
# bucket '0' is 0-100, '100' is 100-200, etc