Advanced Grepping

Shell & Grep: Where we count certain strings in a log file by hour.

for var in `seq 10 23`;
do
echo 'Feb 28 '$var;
grep 'Feb 28 '$var /log/cli/Hanson/2015-02-28.log | grep 'Duplicate order cancel' | wc -l;
done

How can we see: Number of Errors in several files. 

Output as: Number Filename

 grep -RIci "ERROR" . | awk -v FS=":" -v OFS="\t" '$2>0 { print $2, $1 }' | sort -hr