MLDataTable add new column

MLDataTableAddNewColumn.swift

let newColumn = data.map { row -> String in
    guard
        let average = row["deg3"]?.doubleValue
        else {
            fatalError("Missing or invalid columns in row.")
    }
    
    var sentiment = "negative"

    if average < 0
      {sentiment = "negative"}
    else if average == 0
      {sentiment = "neutral"}
    else
      {sentiment = "positive"}
    return sentiment
}