CSV

Go programs can handle CSV. Comma-separated values files are a form of flat databases. They can store small amounts of information in an efficient way.

With Go and the "encoding/csv" package, we can read lines from CSV files. We can invoke, from the "os" package, a method like os.Open to specify a file.

First example

Here we open a file on the disk with os.Open. You will need to change the path to a CSV file that exists (the extension is not important).

package main

import (
    "bufio"
    "encoding/csv"
    "os"
    "fmt"
    "io"
)

func main() {
    // Load a TXT file.
    f, _ := os.Open("C:\\programs\\file.txt")

    // Create a new reader.
    r := csv.NewReader(bufio.NewReader(f))
    for {
        record, err := r.Read()
        // Stop at EOF.
        if err == io.EOF {
            break
        }
        // Display record.
        // ... Display record length.
        // ... Display all individual elements of the slice.
        fmt.Println(record)
        fmt.Println(len(record))
        for value := range record {
            fmt.Printf("  %v\n", record[value])
        }
    }
}
cat,dog,bird
10,20,30,40
fish,dog,snake
[cat dog bird]
3
  cat
  dog
  bird
[10 20 30 40]
4
  10
  20
  30
  40
[fish dog snake]
3
  fish
  dog
  snake

ReadAll, strings

We can read lines from a string. First we must use strings.NewReader and use the string as the argument. We pass that Reader to csv.NewReader.

package main

import (
    "encoding/csv"
    "fmt"
    "strings"
)

func main() {
    // Create a 2-line string.
    data := " fish,blue,water \n fox,red,farm "

    // Use strings.NewReader.
    // ... This creates a new Reader for passing to csv.NewReader.
    r := csv.NewReader(strings.NewReader(data))
    // Read all records.
    result, _ := r.ReadAll()

    fmt.Printf("Lines: %v", len(result))
    fmt.Println()

    for i := range result {
        // Element count.
        fmt.Printf("Elements: %v", len(result[i]))
        fmt.Println()
        // Elements.
        fmt.Println(result[i])
    }
}
Lines: 2
Elements: 3
[ fish blue water ]
Elements: 3
[ fox red farm ]

2D slice

With ReadAll we receive a 2D slice of lines and the values within each line. We can use len to count elements in a line. With append() we can add to this 2D slice.

Advantages

Why not just use a Scanner and Split each line in a file? The csv package can help us avoid some code. We can reuse the code provided in the Go standard library.

A review

The "encoding/csv" package is powerful. We set options on the Reader to handle different formats of files. We read CSV values from a file on the disk.