Question

I am reading two csv files containg a set of attributes

File 1 attributes = name, class, rollno,   
File 2 attributes = rollno, city,town

I need to match the two files and for every matching rollno I have to append the File 2 attributes into File1 and create a csv file in the format
rollno, name, class, city, town

So far I have succeeded in reading the File1 and file2 values into a List of linked hashmaps of the type.

List<Map<Object, Object>> _students = new ArrayList<Map<Object, Object>>();

I am not able to figure out the steps to move forward.

How do I search through the list map of first file for the roll no contained in the second listmap and append it to the firstlistmap?

and then print it to a csv file in the order specified ( I am able to iterate and print all the values in the order they were inserted in the map)

Answer 1

I would approach this problem by reading the first file and store the values in a hashmap. and then append to that hashmap
The key would be the role number and the value would be a list of the the other values.

Map<String, List<String>> map = new HashMap<String, List<String>>()

Pseudocode:

for (List<String> line : file1.lines) {
 List curLine = new LinkedList();
 curLine.add(line.get(0));
 curLine.add(line.get(1));

 map.put(line.get(2),curLine)
}

for (List<String> line : file2.lines) {
 String key = line.get(0);
 String list = map.get(key);
 if (list != null)
 {
  list.add(line.get(1));
  list.add(line.get(2));
 }

 map.put(key,list); // probably not necessary as you change the reference that is already in the map, but I'm not sure

}