As usual, create two directories for today's class. Create a
directory called lecture28 under activities, and
a directory called lab28 under labs.
We have seen a number of data types up to now: int, float, string, boolean even turtle is technically a data type. Today, you will learn your first data structure, lists. Lists are a mechanism for holding other data types. This structure will allow us to store an arbitrary number of values, even if we don't know that number a priori.
The World Series just ended with my favorite team losing. Maybe they would have done better if they had written programs to compute player statistics, like batting average. Batting average is the ratio of hits to at bats. To compute a player's batting average you have to count the different types of hits a player makes.
Create a Python function called
batting_average(appearances) in the same
file. The function parameter, appearances, is a list of ints
that encodes the results of a baseball player's appearances at
batting. Each plate appearance can be interpreted as follows:
| 4 | Home Run |
| 3 | Triple |
| 2 | Double |
| 1 | Single |
| 0 | Walk |
| -1 | Out |
The function should return the batting average for the plate appearances in the list. The batting average can be computed using the following equations:
at_bats = plate_appearances - walks
hits = singles + doubles + triples + home_runs
batting_average = hits / at_bats
>> print(batting_average([1, 1, -1])) 0.6666666666 >> pedroia_at_bats = [-1, 1, -1, -1, 1, -1, -1, 2, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, 0, -1, 0, -1, -1, -1, 2, 1, -1, -1, -1, -1, 1, 0, -1, -1, -1, 1, -1, -1, 1, -1, 1, -1, 0, -1, 1, 1, -1, -1, 2, 0, -1, -1, -1, -1, -1, -1, -1, 1, -1, 2, -1, -1, -1, -1, -1, -1, -1, 1] >> print(batting_average(pedroia_at_bats)) 0.25396825396825395
batting_average function would probably be much
easier if you had some mechanism to count the number of
appearances of some value in the list. Towards that end, create a
Python function called count(a_list, element) in
the same file. The function should return the number of times
element occurs in the the list a_list. It would be
wise to test this function before you try to use it in
batting_average.
Suppose someone comes into the class, and bets you $100 that some two people share a birthday within the individuals of the class. Do you share your birthday with anyone in the class? Is there a shared birthday between any two people in the class? It seems that the odds would be pretty slim. However, if you are putting up $100 on this bet, you might want to figure out your odds of winning this bet.
In a file called birthdays.py, create a function called
shared_probability(group_size). This function takes one
positive integer parameter, the number of people in a given group.
This function should return a floating point value in the range [0, 1], a probability that there is a shared
birthday in a group of size group_size.
What is the minimum group size that the probability exceeds 50%? What is the minimum group size that there is a virtual guarantee (0.9999) there is a shared birthday?
>> print(shared_probability(1)) 0.0 >> print(shared_probability(366)) 1.0
shared_probability function should execute a fixed
number (some constant defined number greater than one) of simulations
for a given group size. Each simulation consists of generating the
requested number of random birthdays and determining if there is a
shared birthday in the group
When you have finished, create a tar file of your lab28
directory. To create a tar file, execute the following commands:
cd ~/cs120/labs tar czvf lab28.tgz lab28/
To submit your activity, go to cseval.roanoke.edu. You should
see an available assignment called Lab Assignment 28. Only
one of your pair should submit your activity. Make sure both partners
are listed in the header of your files.
Do not forget to email your partner today's files!