csvutil/csvdriver: add ability to name columns

[sbinet]

From @sbinet on November 16, 2016 9:15

right now, opening a CSV connection is done like so:

func foo() {
	// Open the CSV file as a database table.
	db, err := csvdriver.Conn{
		File:    "../data/iris.csv",
		Comment: '#',
		Comma:   ',',
	}.Open()
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// Start a database transaction.
	tx, err := db.Begin()
	if err != nil {
		log.Fatal(err)
	}
	defer tx.Commit()

	// Define a SQL query that we will execute against the CSV file.
	query := "SELECT var3, var4, var5 FROM csv WHERE var5 = \"Iris-versicolor\""

	// etc...
}

this makes a query rather cumbersome to read.

it should be possible to open a CSV connection with an optional Columns []string field:

// Open the CSV file as a database table.
db, err := csvdriver.Conn{
	File:    "../data/iris.csv",
	Comment: '#',
	Comma:   ',',
	Columns: []string{"sepal_length", "sepal_width", "petal_length", "petal_width", "species"},
}.Open()

such that the query reads:

// Define a SQL query that we will execute against the CSV file.
query := `SELECT petal_length, petal_width, species FROM csv WHERE species = "Iris-versicolor"`

What do you think @dwhitena ?

Copied from original issue: go-hep/csvutil#2

[dwhitena]

Yes, I like that. In fact you could call this "schema" if you like, because we are really interacting as if it were a database. I guess it depends on how we want the user to think about the interaction. If we are thinking in terms of a DB interaction, I think schema makes sense.