Golang: fetching data from 1 CSV File to anthoer

I am new to golang, and I am trying to fetch 1 csv file to another new csv file, but i need only 2 records from the old csv file.

How would you fetch only the first two records of that file?

Here is what I have tried so far (also in the play.golang.org):

package main
import (
"encoding/csv"
"fmt"
"io"
"os"
)
func main() {
//SELECTING THE FILE TO EXTRACT.......
csvfile1, err := os.Open("data/sample.csv")
if err != nil {
fmt.Println(err)
return
}
defer csvfile1.Close()
reader := csv.NewReader(csvfile1)
for i := 0; i < 3; i++ {
record, err := reader.Read()
if err == io.EOF {
break
} else if err != nil {
fmt.Println(err)
return
}
csvfile2, err := os.Create("data/SingleColomReading.csv")
if err != nil {
fmt.Println(err)
return
}
defer csvfile2.Close()
records := []string{
record,
}
writer := csv.NewWriter(csvfile2)
//fmt.Println(writer)
for _, single := range records {
er := writer.Write(single)
if er != nil {
fmt.Println("error", er)
return
}
fmt.Println(single)
writer.Flush()
//fmt.Println(records)
//a:=strconv.Itoa(single)
n, er2 := csvfile2.WriteString(single)
if er2 != nil {
fmt.Println(n, er2)
}
}
}
}

Fixing your program,

package main
import (
"encoding/csv"
"fmt"
"io"
"os"
)
func main() {
csvfile1, err := os.Open("data/sample.csv")
if err != nil {
fmt.Println(err)
return
}
defer csvfile1.Close()
reader := csv.NewReader(csvfile1)
csvfile2, err := os.Create("data/SingleColomReading.csv")
if err != nil {
fmt.Println(err)
return
}
writer := csv.NewWriter(csvfile2)
for i := 0; i < 2; i++ {
record, err := reader.Read()
if err != nil {
if err == io.EOF {
break
}
fmt.Println(err)
return
}
err = writer.Write(record)
if err != nil {
fmt.Println(err)
return
}
}
writer.Flush()
err = csvfile2.Close()
if err != nil {
fmt.Println(err)
return
}
}

However, since you are only interested in copying records (lines) as a whole and not individual fields of a record, you could use bufio.Scanner, as @VonC suggested. For example,

package main
import (
"bufio"
"fmt"
"os"
)
func main() {
csvfile1, err := os.Open("data/sample.csv")
if err != nil {
fmt.Println(err)
return
}
defer csvfile1.Close()
scanner := bufio.NewScanner(csvfile1)
csvfile2, err := os.Create("data/SingleColomReading.csv")
if err != nil {
fmt.Println(err)
return
}
writer := bufio.NewWriter(csvfile2)
nRecords := 0
for scanner.Scan() {
n, err := writer.Write(scanner.Bytes())
if err != nil {
fmt.Println(n, err)
return
}
err = writer.WriteByte('\n')
if err != nil {
fmt.Println(err)
return
}
if nRecords++; nRecords >= 2 {
break
}
}
if err := scanner.Err(); err != nil {
fmt.Println(err)
return
}
err = writer.Flush()
if err != nil {
fmt.Println(err)
return
}
err = csvfile2.Close()
if err != nil {
fmt.Println(err)
return
}
}

It owuld be easier to:

• read your csv file into a string array (one line per element), for the two first lines only

    var lines []string
  scanner := bufio.NewScanner(file)
  nblines := 0
  for scanner.Scan() {
  lines = append(lines, scanner.Text())
  if nblines++; nblines >= 2 {
  break
  }
  }
  

• Then you can use a range lines to write those two lines in the destination file.
  lines includes at most 2 elements.