Awk/Unix group by

$ awk -F, 'NR>1{arr[$1]++}END{for (a in arr) print a, arr[a]}' file.txt
joe 1
jim 1
mike 3
bob 2

EXPLANATIONS

• -F, splits on ,
• NR>1 treat lines after line 1
• arr[$1]++ increment array arr (split with ,) with first column as key
• END{} block is executed at the end of processing the file
• for (a in arr) iterating over arr with a key
• print a print key , arr[a] array with a key