英文:
Reading CSV file in Go
问题
这是一个读取CSV文件的代码片段：
func parseLocation(file string) (map[string]Point, error) {f, err := os.Open(file)defer f.Close()if err != nil {return nil, err}lines, err := csv.NewReader(f).ReadAll()if err != nil {return nil, err}locations := make(map[string]Point)for _, line := range lines {name := line[0]lat, laterr := strconv.ParseFloat(line[1], 64)if laterr != nil {return nil, laterr}lon, lonerr := strconv.ParseFloat(line[2], 64)if lonerr != nil {return nil, lonerr}locations[name] = Point{lat, lon}}return locations, nil}
有没有办法提高这段代码的可读性？减少 if 和 nil 的噪音。
英文:
Here is a code snippet that reads CSV file:
func parseLocation(file string) (map[string]Point, error) {f, err := os.Open(file)defer f.Close()if err != nil {return nil, err}lines, err := csv.NewReader(f).ReadAll()if err != nil {return nil, err}locations := make(map[string]Point)for _, line := range lines {name := line[0]lat, laterr := strconv.ParseFloat(line[1], 64)if laterr != nil {return nil, laterr}lon, lonerr := strconv.ParseFloat(line[2], 64)if lonerr != nil {return nil, lonerr}locations[name] = Point{lat, lon}}return locations, nil}
Is there a way to improve readability of this code? if and nil noise.
答案1
得分: 79
Go现在有一个用于处理CSV的包，名为encoding/csv。你可以在这里找到文档：https://golang.org/pkg/encoding/csv/
文档中有一些很好的示例。下面是我创建的一个辅助方法，用于读取CSV文件并返回其记录。
package mainimport ("encoding/csv""fmt""log""os")func readCsvFile(filePath string) [][]string {f, err := os.Open(filePath)if err != nil {log.Fatal("无法读取输入文件 " + filePath, err)}defer f.Close()csvReader := csv.NewReader(f)records, err := csvReader.ReadAll()if err != nil {log.Fatal("无法解析CSV文件 " + filePath, err)}return records}func main() {records := readCsvFile("../tasks.csv")fmt.Println(records)}
希望对你有帮助！
英文:
Go now has a csv package for this. Its is encoding/csv. You can find the docs here: https://golang.org/pkg/encoding/csv/
There are a couple of good examples in the docs. Here is a helper method I created to read a csv file and returns its records.
package mainimport ("encoding/csv""fmt""log""os")func readCsvFile(filePath string) [][]string {f, err := os.Open(filePath)if err != nil {log.Fatal("Unable to read input file " + filePath, err)}defer f.Close()csvReader := csv.NewReader(f)records, err := csvReader.ReadAll()if err != nil {log.Fatal("Unable to parse file as CSV for " + filePath, err)}return records}func main() {records := readCsvFile("../tasks.csv")fmt.Println(records)}
答案2
得分: 35
Go是一种非常冗长的语言，但你可以使用类似以下的代码：
// 预先声明 errfunc parseLocation(file string) (locations map[string]*Point, err error) {f, err := os.Open(file)if err != nil {return nil, err}defer f.Close() // 这个需要在 err 检查之后lines, err := csv.NewReader(f).ReadAll()if err != nil {return nil, err}// 在声明中已经定义，不需要 :=locations = make(map[string]*Point, len(lines))var lat, lon float64 // 预先声明 lat, lonfor _, line := range lines {// 更短、更简洁，而且由于已经声明了 lat 和 err，我们可以这样做。if lat, err = strconv.ParseFloat(line[1], 64); err != nil {return nil, err}if lon, err = strconv.ParseFloat(line[2], 64); err != nil {return nil, err}locations[line[0]] = &Point{lat, lon}}return locations, nil}// 编辑[@Dustin](https://stackoverflow.com/users/39975/dustin) 在 [评论](https://stackoverflow.com/questions/24999079/reading-csv-file-in-go/24999351?noredirect=1#comment38921721_24999351) 中发布了一个更高效和正确的版本，我在这里添加它以保证完整性：```gofunc parseLocation(file string) (map[string]*Point, error) {f, err := os.Open(file)if err != nil {return nil, err}defer f.Close()csvr := csv.NewReader(f)locations := map[string]*Point{}for {row, err := csvr.Read()if err != nil {if err == io.EOF {err = nil}return locations, err}p := &Point{}if p.lat, err = strconv.ParseFloat(row[1], 64); err != nil {return nil, err}if p.lon, err = strconv.ParseFloat(row[2], 64); err != nil {return nil, err}locations[row[0]] = p}}
[kbd]playground/kbd
<details><summary>英文:</summary>Go is a very verbose language, however you could use something like this:// predeclare errfunc parseLocation(file string) (locations map[string]*Point, err error) {f, err := os.Open(file)if err != nil {return nil, err}defer f.Close() // this needs to be after the err checklines, err := csv.NewReader(f).ReadAll()if err != nil {return nil, err}//already defined in declaration, no need for :=locations = make(map[string]*Point, len(lines))var lat, lon float64 //predeclare lat, lonfor _, line := range lines {// shorter, cleaner and since we already have lat and err declared, we can do this.if lat, err = strconv.ParseFloat(line[1], 64); err != nil {return nil, err}if lon, err = strconv.ParseFloat(line[2], 64); err != nil {return nil, err}locations] = &Point{lat, lon}}return locations, nil}**//edit**A more efficient and proper version was posted by [@Dustin](https://stackoverflow.com/users/39975/dustin) in the [comments](https://stackoverflow.com/questions/24999079/reading-csv-file-in-go/24999351?noredirect=1#comment38921721_24999351), I'm adding it here for completeness sake:func parseLocation(file string) (map[string]*Point, error) {f, err := os.Open(file)if err != nil {return nil, err}defer f.Close()csvr := csv.NewReader(f)locations := map[string]*Point{}for {row, err := csvr.Read()if err != nil {if err == io.EOF {err = nil}return locations, err}p := &Point{}if p.lat, err = strconv.ParseFloat(row[1], 64); err != nil {return nil, err}if p.lon, err = strconv.ParseFloat(row[2], 64); err != nil {return nil, err}locations[row[0]] = p}}[<kbd>playground</kbd>](http://play.golang.org/p/3YE2pXSF3x)</details># 答案3**得分**: 26我基本上是从这里复制了我的答案：https://www.dotnetperls.com/csv-go。对我来说，这是一个比我在stackoverflow上找到的答案更好的答案。```goimport ("bufio""encoding/csv""os""fmt""io")func ReadCsvFile(filePath string) {// 加载csv文件。f, _ := os.Open(filePath)// 创建一个新的读取器。r := csv.NewReader(f)for {record, err := r.Read()// 在EOF处停止。if err == io.EOF {break}if err != nil {panic(err)}// 显示记录。// ... 显示记录的长度。// ... 显示切片的所有单独元素。fmt.Println(record)fmt.Println(len(record))for value := range record {fmt.Printf(" %v\n", record[value])}}}
英文:
I basically copied my answer from here: https://www.dotnetperls.com/csv-go. For me, this was a better answer than what I found on stackoverflow.
import ("bufio""encoding/csv""os""fmt""io")func ReadCsvFile(filePath string) {// Load a csv file.f, _ := os.Open(filePath)// Create a new reader.r := csv.NewReader(f)for {record, err := r.Read()// Stop at EOF.if err == io.EOF {break}if err != nil {panic(err)}// 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])}}}
答案4
得分: 5
我也不喜欢默认的Reader过于冗长，所以我创建了一个类似于bufio#Scanner的新类型：
package mainimport "encoding/csv"import "io"type Scanner struct {Reader *csv.ReaderHead map[string]intRow []string}func NewScanner(o io.Reader) Scanner {csv_o := csv.NewReader(o)a, e := csv_o.Read()if e != nil {return Scanner{}}m := map[string]int{}for n, s := range a {m[s] = n}return Scanner{Reader: csv_o, Head: m}}func (o *Scanner) Scan() bool {a, e := o.Reader.Read()o.Row = areturn e == nil}func (o Scanner) Text(s string) string {return o.Row[o.Head[s]]}
示例：
package mainimport "strings"func main() {s := `Month,DayJanuary,SundayFebruary,Monday`o := NewScanner(strings.NewReader(s))for o.Scan() {println(o.Text("Month"), o.Text("Day"))}}
https://golang.org/pkg/encoding/csv
英文:
I also dislike the verbosity of the default Reader, so I made a new type that is
similar to bufio#Scanner:
package mainimport "encoding/csv"import "io"type Scanner struct {Reader *csv.ReaderHead map[string]intRow []string}func NewScanner(o io.Reader) Scanner {csv_o := csv.NewReader(o)a, e := csv_o.Read()if e != nil {return Scanner{}}m := map[string]int{}for n, s := range a {m展开收缩= n}return Scanner{Reader: csv_o, Head: m}}func (o *Scanner) Scan() bool {a, e := o.Reader.Read()o.Row = areturn e == nil}func (o Scanner) Text(s string) string {return o.Row[o.Head展开收缩]}
Example:
package mainimport "strings"func main() {s := `Month,DayJanuary,SundayFebruary,Monday`o := NewScanner(strings.NewReader(s))for o.Scan() {println(o.Text("Month"), o.Text("Day"))}}
答案5
得分: -3
您还可以读取目录的内容以加载所有的CSV文件。然后使用goroutines逐个读取这些CSV文件。
csv文件：
101,300.00,11000901,1155686400102,250.99,11000902,1432339200
main.go文件：
const sourcePath string = "./source"func main() {dir, _ := os.Open(sourcePath)files, _ := dir.Readdir(-1)for _, file := range files {fmt.Println("单个文件:")fmt.Println(file.Name())filePath := sourcePath + "/" + file.Name()f, _ := os.Open(filePath)defer f.Close()// os.Remove(filePath)//函数go func(file io.Reader) {records, _ := csv.NewReader(file).ReadAll()for _, row := range records {fmt.Println(row)}}(f)time.Sleep(10 * time.Millisecond) //给GO routines一些时间来执行}}
输出将是：
$ go run main.go
单个文件:batch01.csv[101 300.00 11000901 1155686400][102 250.99 11000902 1432339200]
下面是使用Invoice struct的示例：
func main() {dir, _ := os.Open(sourcePath)files, _ := dir.Readdir(-1)for _, file := range files {fmt.Println("单个文件:")fmt.Println(file.Name())filePath := sourcePath + "/" + file.Name()f, _ := os.Open(filePath)defer f.Close()go func(file io.Reader) {records, _ := csv.NewReader(file).ReadAll()for _, row := range records {invoice := new(Invoice)invoice.InvoiceNumber = row[0]invoice.Amount, _ = strconv.ParseFloat(row[1], 64)invoice.OrderID, _ = strconv.Atoi(row[2])unixTime, _ := strconv.ParseInt(row[3], 10, 64)invoice.Date = time.Unix(unixTime, 0)fmt.Printf("收到发票 `%v`，金额为 $ %.2f \n", invoice.InvoiceNumber, invoice.Amount)}}(f)time.Sleep(10 * time.Millisecond)}}type Invoice struct {InvoiceNumber stringAmount float64OrderID intDate time.Time}
英文:
You can also read contents of a directory to load all the CSV files. And then read all those CSV files 1 by 1 with goroutines
csv file:
101,300.00,11000901,1155686400102,250.99,11000902,1432339200
main.go file:
const sourcePath string = "./source"func main() {dir, _ := os.Open(sourcePath)files, _ := dir.Readdir(-1)for _, file := range files {fmt.Println("SINGLE FILE: ")fmt.Println(file.Name())filePath := sourcePath + "/" + file.Name()f, _ := os.Open(filePath)defer f.Close()// os.Remove(filePath)//funcgo func(file io.Reader) {records, _ := csv.NewReader(file).ReadAll()for _, row := range records {fmt.Println(row)}}(f)time.Sleep(10 * time.Millisecond)// give some time to GO routines for execute}}
And the OUTPUT will be:
> $ go run main.go
SINGLE FILE:batch01.csv[101 300.00 11000901 1155686400][102 250.99 11000902 1432339200]
----------------- -------------- ---------------------- -------
---------------- ------------------- ----------- --------------
> Below example with the Invoice struct
func main() {dir, _ := os.Open(sourcePath)files, _ := dir.Readdir(-1)for _, file := range files {fmt.Println("SINGLE FILE: ")fmt.Println(file.Name())filePath := sourcePath + "/" + file.Name()f, _ := os.Open(filePath)defer f.Close()go func(file io.Reader) {records, _ := csv.NewReader(file).ReadAll()for _, row := range records {invoice := new(Invoice)invoice.InvoiceNumber = row[0]invoice.Amount, _ = strconv.ParseFloat(row[1], 64)invoice.OrderID, _ = strconv.Atoi(row[2])unixTime, _ := strconv.ParseInt(row[3], 10, 64)invoice.Date = time.Unix(unixTime, 0)fmt.Printf("Received invoice `%v` for $ %.2f \n", invoice.InvoiceNumber, invoice.Amount)}}(f)time.Sleep(10 * time.Millisecond)}}type Invoice struct {InvoiceNumber stringAmount float64OrderID intDate time.Time}
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