Reading in CSV data from a file

Let's consider a simple CSV file, which we will return to later, named iris.csv (available here: https://archive.ics.uci.edu/ml/datasets/iris). This CSV file includes four float columns of flower measurements and a string column with the corresponding flower species:

$ head iris.csv 
5.1,3.5,1.4,0.2,Iris-setosa
4.9,3.0,1.4,0.2,Iris-setosa
4.7,3.2,1.3,0.2,Iris-setosa
4.6,3.1,1.5,0.2,Iris-setosa
5.0,3.6,1.4,0.2,Iris-setosa
5.4,3.9,1.7,0.4,Iris-setosa
4.6,3.4,1.4,0.3,Iris-setosa
5.0,3.4,1.5,0.2,Iris-setosa
4.4,2.9,1.4,0.2,Iris-setosa
4.9,3.1,1.5,0.1,Iris-setosa

With encoding/csv imported, we first open the CSV file and create a CSV reader value:

// Open the iris dataset file.
f, err := os.Open("../data/iris.csv")
if err != nil {
    log.Fatal(err)
}
defer f.Close()

// Create a new CSV reader reading from the opened file.
reader := csv.NewReader(f)

Then we can read in all of the records (corresponding to rows) of the CSV file. These records are imported as [][]string:

// Assume we don't know the number of fields per line. By setting
// FieldsPerRecord negative, each row may have a variable
// number of fields.
reader.FieldsPerRecord = -1

// Read in all of the CSV records.
rawCSVData, err := reader.ReadAll()
if err != nil {
    log.Fatal(err)
}

We can also read in records one at a time in an infinite loop. Just make sure that you check for the end of the file (io.EOF) so that the loop ends after reading in all of your data:

// Create a new CSV reader reading from the opened file.
reader := csv.NewReader(f)
reader.FieldsPerRecord = -1

// rawCSVData will hold our successfully parsed rows.
var rawCSVData [][]string

// Read in the records one by one.
for {

    // Read in a row. Check if we are at the end of the file.
    record, err := reader.Read()
    if err == io.EOF {
        break
    }

    // Append the record to our dataset.
    rawCSVData = append(rawCSVData, record)
}