How to Streamline CSV Reading and Writing in Go for Improved Performance?

Efficient CSV Reading and Writing in Go

In the provided Go code, the CSV reading and writing process is causing significant performance issues. To addresses this, let's explore an alternative approach that streamlines these operations.

Reading CSVs Efficiently

Instead of loading the entire CSV file into memory and then processing it, we can leverage the csv.Reader's ability to process one line at a time. This significantly reduces memory usage and improves performance. The following code snippet demonstrates this approach:

<code class="go">func processCSV(rc io.Reader) (ch chan []string) {
    ch = make(chan []string, 10)
    go func() {
        r := csv.NewReader(rc)
        if _, err := r.Read(); err != nil { //read header
            log.Fatal(err)
        }
        defer close(ch)
        for {
            rec, err := r.Read()
            if err != nil {
                if err == io.EOF {
                    break
                }
                log.Fatal(err)

            }
            ch <- rec
        }
    }()
    return
}</code>

This function takes an io.Reader as input and returns a channel that yields slices of strings representing the CSV records.

Writing CSVs Efficiently

Similarly, for writing CSVs, we can use the csv.Writer's method of writing one line at a time to improve performance. The code for efficient CSV writing is largely similar to the CSV reading:

<code class="go">func writeCSV(wc *csv.Writer, data [][]string) {
    go func() {
        defer wc.Flush(nil)
        for _, rec := range data {
            if err := wc.Write(rec); err != nil {
                log.Fatal(err)
            }
        }
    }()
}</code>

This function takes a csv.Writer and a slice of slices of strings (representing the CSV data) as inputs and asynchronously writes the data to the CSV file.

Integration

With the optimized CSV reading and writing functions in place, the main logic of the program can be rewritten to use these functions for improved performance:

<code class="go">func main() {
    recordsCh := processCSV(os.Open("./path/to/datafile.csv"))
    outfile, err := os.Create("./where/to/write/resultsfile.csv"))
    if err != nil {
        log.Fatal("Unable to open output")
    }
    defer outfile.Close()
    writer := csv.NewWriter(outfile)
    writer.Write([]string{"time", "value", "score"})
    for record := range recordsCh {
        time := record[0]
        value := record[1]
        
        // calculate scores; THIS EXTERNAL METHOD CANNOT BE CHANGED
        score := calculateStuff(value)
        
        valueString := strconv.FormatFloat(floatValue, 'f', 8, 64)
        scoreString := strconv.FormatFloat(prob, 'f', 8, 64)
        writer.Write([]string{time, valueString, scoreString})
    }
    writer.Flush()
}</code>

This revised code efficiently reads the CSV file and calculates scores on the fly, while maintaining high performance for both reading and writing.

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