src/main/java/com/conveyal/gtfs/loader/Table.java
public int getKeyFieldIndex(Field[] fields) {
        String keyField = getKeyFieldName();
        return Field.getFieldIndex(fields, keyField);
    }
public int getKeyFieldIndex(Field[] fields) {
        String keyField = getKeyFieldName();
        return Field.getFieldIndex(fields, keyField);
    }
Returns the index of the key field within the array of fields provided for a given table.
@param fields array of fields (intended to be derived from the headers of a csv text file)