func sections() {
    struct LineRow {
        let lineName: String?
        let lineId: String?
        let nodeName: String
    }

    let rows: [LineRow] = [LineRow(lineName: "LINE1", lineId: "1", nodeName: "NODE1-1"),
                           LineRow(lineName: "LINE1", lineId: "1", nodeName: "NODE1-2"),
                           LineRow(lineName: "LINE1", lineId: "1", nodeName: "NODE1-3"),
                           LineRow(lineName: "LINE2", lineId: "2", nodeName: "NODE2-1"),
                           LineRow(lineName: "LINE2", lineId: "2", nodeName: "NODE2-2"),
                           LineRow(lineName: "LINE3", lineId: "3", nodeName: "NODE3-1")]

    struct Sections {
        let lineId: String?
        let lineName: String?
        let nodes: [LineRow]
    }

    let sections = Dictionary(grouping: rows, by: { $0.lineId }).values.compactMap { Sections(lineId: $0.first?.lineId, lineName: $0.first?.lineName, nodes: $0) }.sorted(by: { $0.lineId ?? "" < $1.lineId ?? "" })
    sections.forEach { aSection in
        print("aSection: \(aSection.lineId)")
        aSection.nodes.forEach { print("\t \($0.nodeName)")}
    }
    //NumberOfSection: sections.count
    //NUmberOfRowsInSection: sections[section].nodes.count
    //Element at IndexPath: let person = sections[indexPath.section].nodes[indexPath.row]
}

sections()