cps6-111101Handout

cps6-111101Handout - – items – return(key,value pairs...

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CompSci 6 Introduction to Computer Science November 1, 2011 Prof. Rodger Announcements • No Reading for next time, no RQ • Apt-04 out, due Thursday • Today – Writing Dictionaries/maps – Solving one apt EmailsCourse Dictionaries/Maps • Dictionaries/maps are another way of organizing data • Keys and Values – Each key maps to a value – Some keys can map to the same value – Can change the value a key maps to Example • Each student could be mapped to their favorite ice cream flavor
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Implementing a Dictionary/Map Keys map to values • Create Empty dictionary somemap = {} • Put in a key and its value somemap[“Forbes”] = “Strawberry” • Get a value for a dictionary value = somemap[“Forbes”] OR value = somemap.get(“Forbes”, “default”) • Change a value for a dictionary somemap[“Forbes’] = “Chocolate” More on using a Dictionary/Map • Get all the keys – listKeys = somemap.keys() • Get all the values – listValues = somemap.values() • Other methods – clear – empty dictionary
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Unformatted text preview: – items – return (key,value) pairs – Iteritems – return (key,value) pairs more efficiently – update – update with another dictionary Change Astrachan’s value somemap[“Astrachan”] = Coffee Mocha Value could be a set or list Back to Popular Name Problem: • Given a list of names, determine the most popular first name and print that name with all of its last names. • Input: Names are always two words, names are in a file. If multiple names are on the same line they are separated by a “:” • Output: Most popular first name, followed by a “:”, followed by corresponding last names separated by a blank Now use a dictionary/map • We will write three maps for practice – First name to count of corresponding last names – First name to list of corresponding last names – First name to set of corresponding last names • Which map is most useful to solve this problem? Compare • Using two parallel lists? • Using one dictionary/map...
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cps6-111101Handout - – items – return(key,value pairs...

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