[英]handling multiple-value in single-value context with csv read
試圖從 csv 文件中讀取date
和number
,所以我有以下結構
type Transaction struct {
Warehouse string `json:"warehouse"`
Item string `json:"item"`
Movement string `json:"movement"`
Batch string `json:"batch"`
Date time.Time `json:"transaction_data"`
Quantity uint64 `json:"quantity"`
}
type Transactions struct {
header []string
lines []Transaction
}
並進行如下閱讀:
func main() {
// Reading csv file thread > START //
pairs := []Pair{{"m", 1}, {"d", 0}, {"c", 2}}
fmt.Println(pairs)
// Sort by Key
sort.Sort(ByKey(pairs))
fmt.Println(pairs)
pairs = append(pairs, Pair{"h", 5})
fmt.Println(pairs)
// Reading csv file thread > START //
input := make(chan Transactions)
go func(input_file string) {
var trx Transactions
fr, err := os.Open(input_file)
failOnError(err)
defer fr.Close()
r := csv.NewReader(fr)
rows, err := r.ReadAll()
failOnError(err)
trx.header = rows[0]
for _, row := range rows[1:] {
trx.lines = append(trx.lines, Transaction{
Warehouse: strings.TrimSpace(row[0]),
Item: strings.TrimSpace(row[1]),
Movement: strings.TrimSpace(row[2]),
Batch: strings.TrimSpace(row[3]),
Date: time.Parse("%Y-%m-%d", row[4]), // multiple-value in single-value context error
Quantity: (strconv.ParseFloat(row[5], 64) * 1000).(uint64), // multiple-value in single-value context error
})
}
peopleJson, _ := json.Marshal(trx.lines)
fmt.Println(string(peopleJson))
input <- trx // send data to channel read
}("trx.csv")
<-input // rceive from channel 'read' and assign value to new data variable
// Reading csv file thread < END //
}
並得到2個錯誤:
.\pair.go:73:24: multiple-value time.Parse() in single-value context
.\pair.go:74:34: multiple-value strconv.ParseFloat() in single-value context
我理解原因,這是 time.Parse( time.Parse()
和strconv.ParseFloat()
返回 2 個輸出、值和錯誤,並且可以通過編寫來克服這個問題:
date, _ := time.Parse("%Y-%m-%d", row[4])
// and later:
Date: date,
但我想知道我是否可以避免這種情況,並在同一個命令塊中解決它:
trx.lines = append(trx.lines, Transaction{
Warehouse: strings.TrimSpace(row[0]),
Item: strings.TrimSpace(row[1]),
Movement: strings.TrimSpace(row[2]),
Batch: strings.TrimSpace(row[3]),
Date: ...
Quantity: ...
}
我得到了答案(感謝富有成效的評論,只有富有成效的評論)
解決方案制作一個單獨的 function 讀取 2 上下文,並僅返回如下值:
func mustTime(t time.Time, err error) time.Time { failOnError(err); return t }
func mustNumber(d float64, err error) uint64 { failOnError(err); return uint64(d + 1000) }
然后將其稱為:
Date: mustTime(time.Parse("%Y-%m-%d", row[4])),
Quantity: mustNumber(strconv.ParseFloat(row[5], 64)),
因此,完整正確的代碼變為:
package main
import (
"encoding/csv"
"encoding/json"
"fmt"
"log"
"os"
"sort"
"strconv"
"strings"
"time"
)
func failOnError(err error) {
if err != nil {
log.Fatal("Error:", err)
panic(err)
}
}
type Pair struct {
Key string
Value float64
}
type ByKey []Pair
func (s ByKey) Len() int {
return len(s)
}
func (s ByKey) Swap(i, j int) {
s[i], s[j] = s[j], s[i]
}
func (s ByKey) Less(i, j int) bool {
return s[i].Key < s[j].Key
}
func (s ByKey) pop() bool {
//s = append(s,[0 : s.Len()-1])
return true
}
func main() {
// Reading csv file thread > START //
pairs := []Pair{{"m", 1}, {"d", 0}, {"c", 2}}
fmt.Println(pairs)
// Sort by Key
sort.Sort(ByKey(pairs))
fmt.Println(pairs)
pairs = append(pairs, Pair{"h", 5})
fmt.Println(pairs)
// Reading csv file thread > START //
input := make(chan Transactions)
go func(input_file string) {
var trx Transactions
fr, err := os.Open(input_file)
failOnError(err)
defer fr.Close()
r := csv.NewReader(fr)
rows, err := r.ReadAll()
failOnError(err)
trx.header = rows[0]
for _, row := range rows[1:] {
trx.lines = append(trx.lines, Transaction{
Warehouse: strings.TrimSpace(row[0]),
Item: strings.TrimSpace(row[1]),
Movement: strings.TrimSpace(row[2]),
Batch: strings.TrimSpace(row[3]),
Date: mustTime(time.Parse("%Y-%m-%d", row[4])),
Quantity: mustNumber(strconv.ParseFloat(row[5], 64)),
})
}
peopleJson, _ := json.Marshal(trx.lines)
fmt.Println(string(peopleJson)) // This is working smoothly
input <- trx // send data to channel read
}("trx.csv")
//data :=
<-input // rceive from channel 'read' and assign value to new data variable
// Reading csv file thread < END //
}
type Transactions struct {
header []string
lines []Transaction
}
type Transaction struct {
Warehouse string `json:"warehouse"`
Item string `json:"item"`
Movement string `json:"movement"`
Batch string `json:"batch"`
Date time.Time `json:"transaction_data"`
Quantity uint64 `json:"quantity"`
}
func mustTime(t time.Time, err error) time.Time { failOnError(err); return t }
func mustNumber(d float64, err error) uint64 { failOnError(err); return uint64(d + 1000) }
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