我想从磁盘读取一个 csv 文件到 []map[string]string 数据类型。 []slice 是行号,map["key"] 是 csv 文件的标题(第 1 行)。
我在标准库中找不到任何东西来完成这个。
最佳答案
根据回复,标准库(如 ioutil)中似乎没有任何内容可以将 csv 文件读入 map 。
给定 csv 文件路径的以下函数会将其转换为 map[string]string 的一部分。
更新:根据评论,我决定提供我的 CSVFileToMap() 和 MapToCSV() 函数,将 map 写回.csv 文件。
package main
import (
"os"
"encoding/csv"
"fmt"
"strings"
)
// CSVFileToMap reads csv file into slice of map
// slice is the line number
// map[string]string where key is column name
func CSVFileToMap(filePath string) (returnMap []map[string]string, err error) {
// read csv file
csvfile, err := os.Open(filePath)
if err != nil {
return nil, fmt.Errorf(err.Error())
}
defer csvfile.Close()
reader := csv.NewReader(csvfile)
rawCSVdata, err := reader.ReadAll()
if err != nil {
return nil, fmt.Errorf(err.Error())
}
header := []string{} // holds first row (header)
for lineNum, record := range rawCSVdata {
// for first row, build the header slice
if lineNum == 0 {
for i := 0; i < len(record); i++ {
header = append(header, strings.TrimSpace(record[i]))
}
} else {
// for each cell, map[string]string k=header v=value
line := map[string]string{}
for i := 0; i < len(record); i++ {
line[header[i]] = record[i]
}
returnMap = append(returnMap, line)
}
}
return
}
// MapToCSVFile writes slice of map into csv file
// filterFields filters to only the fields in the slice, and maintains order when writing to file
func MapToCSVFile(inputSliceMap []map[string]string, filePath string, filterFields []string) (err error) {
var headers []string // slice of each header field
var line []string // slice of each line field
var csvLine string // string of line converted to csv
var CSVContent string // final output of csv containing header and lines
// iter over slice to get all possible keys (csv header) in the maps
// using empty Map[string]struct{} to get UNIQUE Keys; no value needed
var headerMap = make(map[string]struct{})
for _, record := range inputSliceMap {
for k, _ := range record {
headerMap[k] = struct{}{}
}
}
// convert unique headersMap to slice
for headerValue, _ := range headerMap {
headers = append(headers, headerValue)
}
// filter to filteredFields and maintain order
var filteredHeaders []string
if len(filterFields) > 0 {
for _, filterField := range filterFields {
for _, headerValue := range headers {
if filterField == headerValue {
filteredHeaders = append(filteredHeaders, headerValue)
}
}
}
} else {
filteredHeaders = append(filteredHeaders, headers...)
sort.Strings(filteredHeaders) // alpha sort headers
}
// write headers as the first line
csvLine, _ = WriteAsCSV(filteredHeaders)
CSVContent += csvLine + "\n"
// iter over inputSliceMap to get values for each map
// maintain order provided in header slice
// write to csv
for _, record := range inputSliceMap {
line = []string{}
// lines
for k, _ := range filteredHeaders {
line = append(line, record[filteredHeaders[k]])
}
csvLine, _ = WriteAsCSV(line)
CSVContent += csvLine + "\n"
}
// make the dir incase it's not there
err = os.MkdirAll(filepath.Dir(filePath), os.ModePerm)
if err != nil {
return err
}
// write out the csv contents to file
ioutil.WriteFile(filePath, []byte(CSVContent), os.FileMode(0644))
if err != nil {
return err
}
return
}
func WriteAsCSV(vals []string) (string, error) {
b := &bytes.Buffer{}
w := csv.NewWriter(b)
err := w.Write(vals)
if err != nil {
return "", err
}
w.Flush()
return strings.TrimSuffix(b.String(), "\n"), nil
}
最后,这里有一个测试用例来展示它的用法:
func TestMapToCSVFile(t *testing.T) {
// note: test case requires the file ExistingCSVFile exist on disk with a
// few rows of csv data
SomeKey := "some_column"
ValueForKey := "some_value"
OutputCSVFile := `.\someFile.csv`
ExistingCSVFile := `.\someExistingFile.csv`
// read csv file
InputCSVSliceMap, err := CSVFileToMap(ExistingCSVFile)
if err != nil {
t.Fatalf("MapToCSVFile() failed %v", err)
}
// add a field in the middle of csv
InputCSVSliceMap[2][SomeKey] = ValueForKey // add a new column name
"some_key" with a value of "some_value" to the second line.
err = MapToCSVFile(InputCSVSliceMap, OutputReport, nil)
if err != nil {
t.Fatalf("MapToCSVFile() failed writing outputReport %v", err)
}
// VALIDATION: check that Key field is present in MapToCSVFile output file
// read Output csv file
OutputCSVSliceMap, err := CSVFileToMap(OutputCSVFile)
if err != nil {
t.Fatalf("MapToCSVFile() failed reading output file %v", err)
}
// check that the added key has a value for Key
if OutputCSVSliceMap[2][SomeKey] != ValueForKey {
t.Fatalf("MapToCSVFile() expected row to contains key value: %v", ValueForKey)
}
}
关于csv - Go stdlib 是否具有将 csv 文件读入 []map[string]string 的功能?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/57102134/