algorithmcodex
diff --git a/‎python/ultimate_utils/07-dictionaries-sets.py‎
Lines changed: 145 additions & 3 deletions b/‎python/ultimate_utils/07-dictionaries-sets.py‎
Lines changed: 145 additions & 3 deletions
@@ -14,7 +14,11 @@
 #Classes have a function __hash__ invoked when used as the key
 print(hash("hello")) 
 
-#Almost always immutable type
+#I'm not sure of exact internals on how the hash is used, but imagine it like so:
+#You have an area of memory with 8 spots, and you need to store the value at some spot...
+print(hash("hello") % 8) 
+
+#Almost always immutable type (should be, anyway)
 #a tuple will work, list will not. a number will work
 
 #Why use a hashtable? Extremely fast to add or look up data
@@ -26,6 +30,8 @@
 
 
 ######### RETRIEVE DATA FROM DICTIONARY ##########
+
+
 print(list(emails))
 print(sorted(emails))
 #print(emails[0]) # NOPE!
@@ -73,6 +79,7 @@
 
 ######### LOOPING THROUGH KEYS #########
 
+
 #dictionary is an iterable (implements __iter__)
 
 emails = {
@@ -86,6 +93,8 @@
     print(k)
 
 #You can use the key to get the element 
+#Not ideal.
+#One reason being the key has to be hashed to get the value associated with it.
 #(but will show better way in next section)
 for k in emails:
     print("index", k, "is", emails[k])
@@ -97,11 +106,36 @@
 #In the prev section we used the index with [].
 #Although it works, you can do this:
 
-for k, elem in emails:
+for k, elem in emails.items():
     print(k, elem)
 
 #Each iteration k will be the key and elem will be the item found at this key.
 
+#As an example of what a hashtable can be used for, you can keep track of occurances:
+
+conjunctions = {"but": 0, "or": 0, "so": 0, "and": 0, "yet": 0, "for": 0, "nor": 0} #fanboys
+
+completely_original_poem = """I still hear your voice when you sleep next to me
+I still feel your touch in my dreams
+Forgive me my weakness, but I don't know why
+Without you it's hard to survive
+'Cause every time we touch, I get this feeling
+And every time we kiss I swear I could fly
+Can't you feel my heart beat fast, I want this to last
+Need you by my side"""
+
+words = completely_original_poem.split()
+
+for word in words:
+    if str.lower(word) in conjunctions:
+        conjunctions[str.lower(word)] += 1
+
+print(conjunctions)
+
+#This could easily be wrapped in a function to take a msg and words to look for, returning a dict
+#concept can be used to analyze documents to quantify how vulgar they are, search for phrases, etc
+#dictionaries can be used to keep track of values that are hard to calculate (memoization)
+
 
 ######### SETS EXPLAINED #########
 
@@ -110,9 +144,117 @@
 #Sets are similar to lists in that they just contain the data and not a key-value pair
 #Sets are different than lists in that you cannot have duplicates
 
+stuff = {"sword", "rubber duck", "sice a pizza"}
+print("sword" in stuff)
+print(stuff)
+stuff.add("sword")
+print(stuff)
+#Notice only one occurance of sword even though already added
+
+#How is a set different than a dictionary?
+#For a set, each element is only one piece of data
+#for a dictionary, it is a key-value pair. 
+
+#Behind the scenes, they both use hashing. The hashing is used to determine where to store the data.
+#For dictionaries, the KEY is hashed
+#for sets, we do not have a key, so the data itself is hashed.
+#This means we cannot store something in sets that is not hashable.
+
+#stuff.add(["trying to add a list"])
+
+#It's important to understand the purpose of a set...
+#Easily check if element in set
+#such as to easily check to see if something has been tagged
+#To do various set operations (coming soon)
+
+#An example would be to see if a word is ever used in a phrase. Not counted (that wold be a dictionary)
+
+conjunctions = {"but", "or", "so", "and", "yet", "for", "nor"} #fanboys
+seen = set() #THERE'S NOT AN EMPTY SET LITERAL!! #learn something new every day
+completely_original_poem = """I still hear your voice when you sleep next to me
+I still feel your touch in my dreams
+Forgive me my weakness, but I don't know why
+Without you it's hard to survive
+'Cause every time we touch, I get this feeling
+And every time we kiss I swear I could fly
+Can't you feel my heart beat fast, I want this to last
+Need you by my side"""
+
+words = completely_original_poem.split()
+
+for word in words:
+    if str.lower(word) in conjunctions:
+        seen.add(str.lower(word))
+
+print(seen)
 
-#we used set with list com STOPPED HERE
 
 ######### REMOVE DUPLICATES FROM LIST / CREATE SET FROM LIST ##########
+
+#You can remove duplicate elements from a list by converting it to a set and back. 
+
+colors = ["red", "red", "green", "green", "blue", "blue", "blue"]
+
+print(id(colors), colors)
+
+colors[:] = list(set(colors))
+
+print(id(colors), colors)
+
+
+#Earlier on in our life I showed some code to count each type of element in a list. 
+
+colors = ["red", "red", "green", "green", "blue", "blue", "blue"]
+
+counts = [[colors.count(item), item] for item in set(colors)]
+
+print(counts)
+
+#This works because is iterates through the set {"red", "green", "blue"} counting each in colors
+
+
 ######### UNION AND INTERSECTION #########
+
+my_fav = {"red", "green", "black", "blue", "purple"}
+her_fav= {"blue", "orange", "purple", "green"}
+
+#union
+all_favs = my_fav | her_fav
+print(all_favs) #no repetition
+#You may see + to combine lists, in which there are repeats.
+#But we are not working with lists...so i'll try to focus here.
+
+#intersection (elements shared between both)
+wedding_colors = my_fav & her_fav
+print(wedding_colors)
+#this is like the inside section of a venn diagram
+
+#There are also method versions:
+all_favs = my_fav.union(her_fav)
+print(all_favs)
+
+wedding_colors = my_fav.intersection(her_fav)
+print(wedding_colors)
+
+
 ######### DIFFERENCE AND SYMMETRIC DIFFERENCE ######### 
+
+
+my_fav = {"red", "green", "black", "blue", "purple"}
+her_fav= {"blue", "orange", "purple", "green"}
+
+#Difference
+only_my_colors = my_fav - her_fav
+print(only_my_colors) #elements in left getting rid of all in right. 
+#Could go other way too:
+only_her_colors = her_fav - my_fav
+print(only_her_colors)
+
+#symmetric difference is like if you took colors only I liked union with colors only she liked and put em together:
+
+symmetric = my_fav ^ her_fav
+print(symmetric)
+
+#This is like:
+symmetric = only_my_colors | only_her_colors
+print(symmetric)