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Community Data Science Course (Spring 2019)/Day 3 Notes
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==Online Data Sets: An Important Question== Can you get bulk access to data? '''Bad Signs''' You must authenticate as a particular user in order to access data, and you can only see data for that user. For example: you must log into instagram's api as a particular user [https://www.instagram.com/developer/endpoints/users/ Look at this link!] '''Good signs''' The organization owning the data wants everyone to access it. Like wikipedia or most government data. You may have to authenticate as a particular user, but you can access general data. For example: once you log into Twitter, you can get all tweets about a place [https://developer.twitter.com/en/docs/geo/place-information/api-reference/get-geo-id-place_id Twitter API Docs] ==Dictionaries== * Use dictionaries to store key/value pairs. * Dictionaries do not guarantee ordering. * A given key can only have one value, but multiple keys can have the same value. ====Initialization==== >>> my_dict = {} >>> my_dict {} >>> your_dict = {"Alice" : "chocolate", "Bob" : "strawberry", "Cara" : "mint chip"} >>> your_dict {'Bob': 'strawberry', 'Cara': 'mint chip', 'Alice': 'chocolate'} ====Adding elements to a dictionary==== >>> your_dict["Dora"] = "vanilla" >>> your_dict {'Bob': 'strawberry', 'Cara': 'mint chip', 'Dora': 'vanilla', 'Alice': 'chocolate'} ====Accessing elements of a dictionary==== >>> your_dict["Alice"] 'chocolate' >>> your_dict.get("Alice") 'chocolate' >>> your_dict["Eve"] Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: 'Eve' >>> "Eve" in your_dict False >>> "Alice" in your_dict True >>> your_dict.get("Eve") >>> person = your_dict.get("Eve") >>> print(person) None >>> print(type(person)) <type 'NoneType'> >>> your_dict.get("Alice") 'chocolate' ====Changing elements of a dictionary==== >>> your_dict["Alice"] = "coconut" >>> your_dict {'Bob': 'strawberry', 'Cara': 'mint chip', 'Dora': 'vanilla', 'Alice': 'coconut'} ====Histograms==== '''Challenge''': using wordplay example from last week, count the number of words that start with each letter. This kind of problem is very common Data Science, and it is easy with a dictionary. (note: I will post the solution after class) ====For-loops and dictionaries==== There are two common ways to iterate through dictionaries: >>> ages = {'Tommy': 34, Heather: 30, 'Joanna': 20} >>> for key in ages: >>> print(key + " is " + str(ages[key]) + " years old") >>> for key, value in ages.items(): >>> print(key + " is " + str(value) + " years old")
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