# [Tutor] Functional question

Bernard Lebel 3dbernard at gmail.com
Fri Aug 5 22:14:44 CEST 2005

```Hello,

This question is not strictly bound to Python, but rather some
functional programming problem, I hope someone can help me or suggest
ressources.

1 --
I have a list of lists. Each of these lists has 3 elements: a string,
and two integers. Thoughout the lists, there are only two different
integers for the first one, and two different for the second one.

aLists = [
[ 'Pass1', 10, 200 ],
[ 'Pass2', 10, 200 ],
[ 'Pass3', 25, 100 ],
[ 'Pass4', 10, 100 ],
[ 'Pass5', 25, 200 ] ]

2 --
Then I want to regroup the strings into two dictionaries. The first
dictionaries is for the strings that have the same first integer, and
the second dictionay is for the strings that have the same second
integer.

dMap1 = {}
dMap2 = {}

# Iterate lists
for aList in aLists:

sPass = aList[0]
iValue1 = aList[1]
iValue2 = aPList[2]

# Map pass name to integers
dMap1.setdefault( iValue1, [] ).append( sPass )
dMap2.setdefault( iValue2, [] ).append( sPass )

So far so good, it's working, I end up with this structure:

dMap1 = {
10 : [ 'Pass1', 'Pass2', 'Pass4' ],
25 : [ 'Pass3', 'Pass5' ] }

dMap2 = {
100 : [ 'Pass3', 'Pass4' ],
200 : [ 'Pass1', 'Pass2', 'Pass5' ] }

3 --
This is where I'm completely stump.
I want to consolidate the strings into another dictionary the strings
that share the same integers, resulting in such a structure:

dGroups = {
'group0' : [ 'Pass1', 'Pass2' ],	     # 10, 200
'group1' : [ 'Pass4' ],				# 10, 100
'group2' : [ 'Pass3' ],				# 25, 100
'group3' : [ 'Pass5' ],				# 25, 200 }

However, I have absolutely no idea how to achieve that third dictionary!

Thanks
Bernard
```