build Friendships Adjacency List

buildFriendshipsAdjacencyList

#
# You have data for social network on who is friends with whom.
# You need to write a function that returns this data in the form of an adjacency list representation, i.e. a mapping of each employee ID to a list of his/her friends on the site
# #
# You have two input data sets to work with. The first data set is the employees at your company, and the second is all the pairs of employees who are virtually friends so far. It does not matter which employee's ID is in which column, the friendships are bidirectional.
#
# employees_input = [
#   "1,Richard,Engineering",
#   "2,Erlich,HR",
#   "3,Monica,Business",
#   "4,Dinesh,Engineering",
#   "6,Carla,Engineering",
# ]
#
# friendships_input = [
#   "1,2",
#   "1,3",
#   "2,4",
# ]
#
# Answers: (Format does not matter)
# 1: 2, 3
# 2: 1, 4
# 3: 1
# 4: 2
# 6: None
#
  
# ITER1:  load key to LIST of TO friends from SRC friend
# ITER2:  REvERSE-SWAP SRC DEST and do above
# ITER3:  original friends list DRIVEs the total key entries!

# ATTN to what MATTERs:
# - NOT MATTER
#   integer formatting conversion does NOT matter, as String char assoc is OK
#   to ensure uniqueness
# - RESTATE PROBLEM
# - BREAKDOWN CASES => TDD!
# - NOT GENERALIZE if unecessary for direction 
#   code what you know you need first, then tweak for variations LATER
# - SPEED is to just LOOP code with indices swapped instead of parameterizing function direction for SRC and DEST -- or LOOP WITHOUT EXTRA function
# - SPEED is to use SHORTER variable names
# - ATTN for Python3 is not to do a get with None default and check isNone
#   BUT INSTEAD need to check if X in Keys FIRST to PREVENT OVERWRITE of
#   if it doesn't already exist
#   -- OTHERWISE, read-access may throw a KEY error!

def loadFriendsBiDirection(directedFriendsPairs):
  
    adjacentFriendsFromSrc = {}
            
    for aPair in directedFriendsPairs:
    
        # TRICK: parsout to good tuple element names instead of just tuple reference [0] [1]
        src, dest= aPair.split(",")
        
        # repeate mapping 2X, once for each direction; no separate function overhead
        for i in range(0, 2):
            
            # save src -> dest
            if (src in adjacentFriendsFromSrc):
              adjacentFriendsFromSrc[src].append(dest)
            else:
              adjacentFriendsFromSrc[src] = [ dest, ]
              
            # TRICK:  Python SWAP
            # now, for BI-directional, SWAP dest as src, in OPPOSITE mapping!
            src, dest = dest, src
           
    return adjacentFriendsFromSrc
    
def fillPeopleWithoutFriends(allPeople, adjacentFriendsFromSrc):
    
    for oneEmployee in employees_input:
        empID, empName, empJob = oneEmployee.split(",")
        if (empID in adjacentFriendsFromSrc):
            # checking for not in is expensive, so just do pass, ELSE
            pass
        else:
            # initialize to NO friends
            adjacentFriendsFromSrc[empID] = []
    
    return adjacentFriendsFromSrc
    
# ******************** TDD DRIVER Script  *************************

input_directed_friendships = [
  "1,2",   
  "1,3",
  "2,4",
]

employees_input = [
"1,Richard,Engineering",
"2,Erlich,HR",
"3,Monica,Business",
"4,Dinesh,Engineering",
"6,Carla,Engineering",
]

# expected_adjacentFriendsFromSrc = 
# 1: 2, 3
# 2: 1, 4
# 3: 1
# 4: 2
# 6: None

adjacentFriendsFromSrc = loadFriendsBiDirection(input_directed_friendships)

adjacentFriendsFromSrc = fillPeopleWithoutFriends(employees_input,   
                                                  adjacentFriendsFromSrc)

print("FRIENDS FROM SRC:  BI-DIRECTIONAL, and THOSE WITH NO FRIENDS!")
print(adjacentFriendsFromSrc)    
  
  
# ************* ASIDE: String-parsing in Python3 and FP operators ****************
# GOTCHA in PYTHON 3:  map, filter, etc return GENERATORS, NOT materialized Lists
# string-parsing tricks
print("\n\nPARSING TRICKS")
# - split to element
# - filter out None
# - convert to int
# - convert to tuple
directedPair = "1,2"
a = directedPair.split(',')
print(a)
print(a[0])
print(a[1])

src, dest = directedPair.split(',')
print(src)
print(dest)

print("FUNCTIONAL TRICKS")
lambda x: x % 2
# https://stackoverflow.com/questions/13638898/how-to-use-filter-map-and-reduce-in-python-3
# https://www.python-course.eu/python3_lambda.php
nums = [2,3,4,5]
odds = list(filter(lambda x: x % 2, nums))
print(odds)