Turn a flattened datasource into a hierarchical one

Let's say I have a table such as:

D_ID    C_ID    B_ID    A_ID
1D      1C      1B      1A
4D      2C      6B      1A
6D      1C      1B      1A
9D  开发者_如何学JAVA    1C      1B      1A
8D      2C      6B      1A

And let's say that structurally speaking, I know the following:

A's
 B's
  C's
   D's

That is D's are children of C's, C's of B's and so on.

How could I turn the table up top into a hierarchical data source? Such as

ID ParentID
1D  1C
4D  2C
6D  1C
9D  1C
8D  2C
1C  1B
2C  6B
1B  1A
6B  1A
1A  Null

This could then serve as a hierarchical datasource for a Telerik TreeView or other hierarchical controls? I know I could iterate over every item and build it myself, but I am wondering if there are better known ways to iterate this. Perhaps even a built in way to achieve this.

---

You could write a simple iteration passing through the file and adding pairs of elements to a dictionary. In pythonish looking psuedo code:

// open the file you want to parse.
file = open(my_log_file)

// create a hash map from ID to parent.
dictionary = {}

// read through the file line by line
for line in file.getlines():
   // ignore first line ...
   // read the 4 columns in each line
   columns[] = line.split(" ")

   // add pairs (id=column[i], parent=column[i+1]) to the hashmap
   dictionary[column[1]] = column[2]
   dictionary[column[2]] = column[3]
   dictionary[column[3]] = column[4]
   dictionary[column[4]] = Nil


// output the hashmap line by line.
print "ID", "Parent ID"
for (id, parent) in dictionary:
  print id, parent

I hope this helps.

---

Here is a quick thought....

If I understand this correctly you can just iterate across the list from right to left, and read pairs... Use a dictionary/map/hashtable to keep them organized. You may need to define a custom comparator for it but thats not too hard.

So as you iterate along from right to left, top to bottom, you add the pairs as you read them so..

parent = "1A";
child = "1B";
list.add(child, parent);
//Then on the next iteration.....
parent = "1B";
child = "1C";

And so on you go...

This way using the child as the key, you are left with a list of all the unique values, this becomes your ID column.

Then your list.values() becomes your ParentID column since it will contain the duplicates for all of the parents that had more than one child. This is also why the child works perfectly as the key since you can only be born once, but you can have many children.

EDIT: BAH! Someone beat me to it with a much more complete version of what I was proposing anyway... oh well. I like my verbal description better ;)