How do I solve Golang filepath.walkfunc problem? - csv

Question

I'm trying to solve a task where I must to find one file with data in CSV format among other files with similar names and same size and print a number on 5th row 3rd column (indexes 4 and 2)
So I wrote this code
package main
import (
"encoding/csv"
"fmt"
"os"
"path/filepath"
)
var s [][]string
func walkfunc(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
buf, err1 := os.Open(path)
if err1 == nil {
var err2 error
r := csv.NewReader(buf)
s, err2 = r.ReadAll()
if err2 == nil {
fmt.Printf("found: %v", s[4][2])
}
}
defer buf.Close()
return nil
}
func main() {
const root = "./task/"
if err := filepath.Walk(root, walkfunc); err != nil {
fmt.Printf("error: %v", err)
}
}
And I got this in output
GOROOT=/usr/local/go #gosetup
GOPATH=/usr/local/go/bin #gosetup
/usr/local/go/bin/go build -o /private/var/folders/j2/ybr0drz13yq31dc67zmvkb1w0000gn/T/GoLand/___go_build_qwasd3_go /Users/user/Downloads/zadacha/qwasd3.go #gosetup
/private/var/folders/j2/ybr0drz13yq31dc67zmvkb1w0000gn/T/GoLand/___go_build_qwasd3_go
panic: runtime error: index out of range [4] with length 3
goroutine 1 [running]:
main.walkfunc({0x14000018120?, 0x0?}, {0x14000098d88?, 0x10247fe40?}, {0x0?, 0x0?})
/Users/user/Downloads/zadacha/qwasd3.go:23 +0x28c
path/filepath.walk({0x14000018120, 0xe}, {0x1024c9cf8, 0x140000685b0}, 0x1024c9338)
/usr/local/go/src/path/filepath/path.go:433 +0xd0
path/filepath.walk({0x10248d4a8, 0x7}, {0x1024c9cf8, 0x140000684e0}, 0x1024c9338)
/usr/local/go/src/path/filepath/path.go:457 +0x1fc
path/filepath.Walk({0x10248d4a8, 0x7}, 0x1024c9338)
/usr/local/go/src/path/filepath/path.go:520 +0x6c
main.main()
/Users/user/Downloads/zadacha/qwasd3.go:37 +0x30
Process finished with the exit code 2
What am I doing wrong?
I was trying to run this code on MacBook.
The needed file contains table with numbers and I need to print a number on 5th row and 3rd column.

Answer 1

As other comments have pointed out, you need to check each CSV to make sure it's actually as big as you expect it to be. You could also add a simple check to try and make sure it's a CSV file before opening it by looking for a ".csv" extension.
Though, to directly address your error... The CSV reader may be able to interpret a plain txt file as CSV and not return an err, like:
buf := strings.NewReader(`A regular text file with 3 lines.
Line2
Line3
`)
r := csv.NewReader(buf)
records, err := r.ReadAll()
if err != nil {
fmt.Println("could not read all of CSV file!")
return err
}
fmt.Println(records)
prints:
[[A regular text file with 3 lines.] [Line2] [Line3]]
Just assuming that it's a CSV with the correct number of rows and columns:
fmt.Println("found", records[4][2])
gives the panic message you shared:
panic: runtime error: index out of range [4] with length 3
You at least need to check that your CSV has 5 rows, and if it does, then check if the 5th row has 3 columns before you try to read that field:
if len(records) < 5 {
fmt.Println(path, "does not have 5 rows")
return nil
}
if len(records[4]) < 3 {
fmt.Println(path, "5th row does not have 3 columns")
return nil
}
fmt.Println("found", records[4][2])
You could also do, inside your walkfunc, a basic check of the file path itself to see if it looks like a CSV:
if strings.ToLower(path[len(path)-4:]) != ".csv" {
fmt.Println(path, "is not a CSV")
return nil
}
I show all this code, plus a fully worked/integrated example in this Playground.