task1.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
)

func main() {
	file, err := os.Open(os.Args[1])
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to open test.medium: %v\n", err)
		os.Exit(-1)
	}
	scanner := bufio.NewScanner(file)
	nLines := 0

	scanner.Scan()
	nCols := len(strings.Split(scanner.Text(), ","))

	sums := make([]int, nCols)

	for scanner.Scan() {
		values := strings.Split(scanner.Text(), ",")
		for i := 0; i < len(sums); i++ {
			nLines++
			intVal, err := strconv.Atoi(values[i])
			if err != nil {
				fmt.Fprintf(os.Stderr, "invalid number: %v\n", values[i])
			}
			sums[i] += intVal
		}
	}
	for _, arg := range os.Args[2:] {
		argTokens := strings.Split(arg, "=")
		colNumInt, err := strconv.Atoi(argTokens[0])
		if err != nil {
			fmt.Fprintf(os.Stderr, "syntax error\n")
		}
		switch argTokens[1] {
		case "MEAN":
			fmt.Printf("mean[%v]: %v\n", colNumInt, sums[colNumInt]/nLines)
		case "SUM":
			fmt.Printf("sum[%v]: %v\n", colNumInt, sums[colNumInt])
		}
	}
}