Lab 8, CSCI 127, Introduction to Computer Science, Hunter College, CUNY, Fall 2024

Counting Tickets per Car

How can tell which car got the most tickets? First, we need to figure out a unique way to identify different cars. Luckily, cars almost always have license plates-- with each state having a unique number. (For this simple exercise, we'll assume that each license plate is unique on its own-- not an unreasonable assumption since every state has a different schema for assigning numbers, but to be more accurate we should keep track of license plate number and issuing state.)

Open up the CSV file and look at the columns. Which column contains the license plate number? Here's all the column names (first line of tickets.csv):

Summons Number,Plate ID,Registration State,Plate Type,Issue Date,Violation Code,Vehicle Body Type,Vehicle Make,Issuing Agency,Street Code1,Street Code2,Street Code3,Vehicle Expiration Date,Violation Location,Violation Precinct,Issuer Precinct,Issuer Code,Issuer Command,Issuer Squad,Violation Time,Time First Observed,Violation County,Violation In Front Of Or Opposite,House Number,Street Name,Intersecting Street,Date First Observed,Law Section,Sub Division,Violation Legal Code,Days Parking In Effect    ,From Hours In Effect,To Hours In Effect,Vehicle Color,Unregistered Vehicle?,Vehicle Year,Meter Number,Feet From Curb,Violation Post Code,Violation Description,No Standing or Stopping Violation,Hydrant Violation,Double Parking Violation

It's the second column: Plate ID. Scanning the CSV file, it looks like most cars got one or two tickets. How can we get the worst offenders (i.e. those cars that got the most parking tickets)?

Let's use Pandas to read in the CSV file, following the same pattern as last lab:

#CSci 127 Teaching Staff
#October 2018
#Count which cars got the most parking tickets

#Import pandas for reading and analyzing CSV data:
import pandas as pd

csvFile = "tickets.csv"			#Name of the CSV file
tickets = pd.read_csv(csvFile)		#Read in the file to a dataframe
print(tickets) 				#Print out the dataframe

Try running your program. It should print out all the information about all the tickets issued. Let's focus in on just licence plates. Change the last line of your program to be:

print(tickets["Plate ID"])	#Print out licence plates

When you run the program again, you should just see the row number and licence plate recorded for each row.

We want to refine this further to print how many tickets each car got. Pandas has a function just for counting occurrences, called value_counts(). Let's modify our last line again to use it:

print(tickets["Plate ID"].value_counts())	#Print out plates & number of tickets each got

Rerunning the program, there are a lot of cars that got only a single ticket. If you scroll back up the Python shell, you will see the cars with the most tickets are listed first. Let's just print out the 10 cars that got the most tickets. We can do this by slicing to [:10]:

print(tickets["Plate ID"].value_counts()[:10])	#Print 10 worst & number of tickets

Even with only 1000 lines of ticket information, there is a car (with plate TOPHAT5) that got more than 5 tickets.

Let's make our program a bit more general, to allow the user to enter their own file name:

#CSci 127 Teaching Staff
#October 2018
#Count which cars got the most parking tickets

#Import pandas for reading and analyzing CSV data:
import pandas as pd

csvFile = input('Enter CSV file name: ')         #Name of the CSV file
tickets = pd.read_csv(csvFile)     #Read in the file to a dataframe
print("The 10 worst offenders are:")
print(tickets["Plate ID"].value_counts()[:10]) #Print out the dataframe

And run it on the tickets.csv data

You should see output:

Enter CSV file name: tickets.csv
The 10 worst offenders are:
Plate ID
TOPHAT5    6
GXP4564    4
XBLD33     4
T63FNW     4
XANK43     3
R12FGF     3
TOPHAT9    3
XP627S     3
GN8063     3
ZDH5639    3
Name: count, dtype: int64

Binning Other Data

Now that you have a program to use as a basic template, answer the following questions:

What color of car is most likely to get a ticket?
What type of license gets the most tickets?
Which location yields the most tickets?

(Remember to check the CSV file for the name used for the columns and use that as the index.)

Top Down Design

Functions are used to design programs and provide an elegant way to divide work among several programmers. A standard technique, called top-down design, consists of breaking a program into multiple function calls (covered in more detail in Section 6.8). Each function is written separately and then tested, before the next function is written.

In today's lab, we will write a program to draw images using turtles. We will focus on breaking down the problem into functions, and then implementing (and testing!) each function separately. Here's a basic outline of our program:

#Intro Programming Lab:  A program with a herd of turtles

import turtle

def main():
    welcomeMessage()            #Writes a welcome message to the shell
    numTurtles = getInput()     #Ask for number of turles
    w = setUpScreen()           #Set up a green turtle window
    turtleList = setUpTurtles(numTurtles) #Make a list of turtles, different colors
    for i in range(10):
        moveForward(turtleList) #Move each turtle in the list forward
        stamp(turtleList)       #Stamp where the turtle stopped


if __name__ == "__main__":
    main()

We will fill in each function, one-by-one, using the comments as guidance. If you run the program above, you will get errors saying that it does not recognize welcomeMessage(), since it is not pre-defined function, but instead a function that we are designing. To avoid these errors and to allow testing of each part as we write it, we will add in empty functions (often called ``stubs'') that we will fill in as we go:

#Intro Programming Lab:  A program with a herd of turtles

import turtle

def welcomeMessage():
    #Empty placeholder until function is defined
    return()

def getInput():
    #Empty placeholder until function is defined
    return()

def setUpScreen():
    #Empty placeholder until function is defined
    return()

def setUpTurtles(num):
    #Empty placeholder until function is defined
    return()

def moveForward(tList):
    #Empty placeholder until function is defined
    return()

def stamp(tList):
    #Empty placeholder until function is defined
    return()

def main():
    welcomeMessage()            #Writes a welcome message to the shell
    numTurtles = getInput()     #Ask for number of turles
    w = setUpScreen()           #Set up a green turtle window
    turtleList = setUpTurtles(numTurtles) #Make a list of turtles, different colors
    for i in range(10):
        moveForward(turtleList) #Move each turtle in the list forward
        stamp(turtleList)       #Stamp where the turtle stopped


if __name__ == "__main__":
    main()

The first function should welcome the user to the program:

def welcomeMessage():
    print()
    print("Welcome to our herd of turtles demonstration!")
    print()

Add it to the program above (replace the empty function with this one) and run it to make sure there are no typos or errors.

Next, let's ask the user for the number of turtles. Since the function call is on the right hand side of an equals sign, it returns a value (namely, the number of turtles) that we will use later in the program. So, our function will ask the user for the number and then use a return statement to send that value back to the calling function:

def getInput():
    n = eval(input("Please enter the number of turtles: "))
    return(n)

When we add these in, we now have the program:

#Intro Programming Lab:  A program with herd of turtles

import turtle


def welcomeMessage():
    print()
    print("Welcome to our herd of turtles demonstration!")
    print()

def getInput():
    n = eval(input("Please enter the number of turtles: "))
    return n

def setUpScreen():
    #Empty placeholder until function is defined
    return()

def setUpTurtles(num):
    #Empty placeholder until function is defined
    return()

def moveForward(tList):
    #Empty placeholder until function is defined
    return()

def stamp(tList):
    #Empty placeholder until function is defined
    return()


def main():
    welcomeMessage()            #Writes a welcome message to the shell
    numTurtles = getInput()     #Ask for number of turles
    w = setUpScreen()           #Set up a green turtle window
    turtleList = setUpTurtles(numTurtles) #Make a list of turtles, different colors
    for i in range(10):
        moveForward(turtleList) #Move each turtle in the list forward
        stamp(turtleList)       #Stamp where the turtle stopped


if __name__ == "__main__":
    main()

We still need to set up the turtle window and make it green. The turtle command to change the background color is bgcolor and colors can be referred by their names or the percentage of red, green, and blue ('RGB') in the color. Let's use the name to change the window color:

def setUpScreen():
    w = turtle.Screen()
    w.bgcolor("green")
    return w

Next, we need to set up a list of turtles. From the function invocation in the main() we know it has the outline:

def setUpTurtles(n):
    #Create a list of turtles
    #Make each turtle appear turtle-shaped
    #Change the color and default direction (so they don't run over each other)
    return tList

To set up our list, we will follow our outline from the strings and lists chapter:

Create an empty list
Make a new item

For our turtles, this looks like:

def setUpTurtles(n):
    tList = []
    #Create turtles:
    for i in range(n):
        t = turtle.Turtle()
        t.shape("turtle")       #Make the turtle appear turtle-shaped
        tList.append(t)

    return tList

Lastly for this function, we need to change the color and direction. We will use the `red-blue-green' (`RGB') values to give each turtle a different color. To keep the turtle color from clashing with the green background, we will set the red and green parts of the color to 0, and just allow the blue to change from 50% to 100%. To spread the turtles out, we'll divide the circle into even angles:

def setUpTurtles(n):
    tList = []
    #Create turtles:
    for i in range(n):
        t = turtle.Turtle()
        t.shape("turtle")       #Make the turtle appear turtle-shaped
        tList.append(t)

    #Change their color from the blue default and default direction
    for i in range(n):
        tList[i].color(0,0,i/(2*n)+.5)
        tList[i].right(i*360/n)

    return tList

If you run your program, you will see the turtles arranged pointing outwards from a center point, in different shapes of blue.

The next functions of the program are straightforward. We will move each turtle forward using a for-loop. We chose 30 by experimenting with window size. If it does not fit well on your screen, change the forward distance to something that does. To make a stamp of where the turtle has been, we use the Turtle graphics function, stamp()

def moveForward(tList):
    for t in tList:
        t.forward(30)

def stamp(tList):
    for t in tList:
        t.stamp()

Putting all the pieces together, we get:

#Intro Programming Lab:  A program with herd of turtles

import turtle


def welcomeMessage():
    print()
    print("Welcome to our herd of turtles demonstration!")
    print()

def getInput():
    n = eval(input("Please enter the number of turtles: "))
    return n


def setUpScreen():
    w = turtle.Screen()
    w.bgcolor("green")
    return w

def setUpTurtles(n):
    tList = []
    #Create turtles:
    for i in range(n):
        t = turtle.Turtle()
        t.shape("turtle")       #Make the turtle appear turtle-shaped
        tList.append(t)

    #Change their color from the blue default and default direction
    for i in range(n):
        tList[i].color(0,0,i/(2*n)+.5)
        tList[i].right(i*360/n)

    return tList

def moveForward(tList):
    for t in tList:
        t.forward(30)

def stamp(tList):
    for t in tList:
        t.stamp()

def main():
    welcomeMessage()            #Writes a welcome message to the shell
    numTurtles = getInput()     #Ask for number of turles
    w = setUpScreen()           #Set up a green turtle window
    turtleList = setUpTurtles(numTurtles) #Make a list of turtles, different colors
    for i in range(10):
        moveForward(turtleList) #Move each turtle in the list forward
        stamp(turtleList)       #Stamp where the turtle stopped


if __name__ == "__main__":
    main()

Challenges

Try running your program. What happens? How could you modify it to make green turtles on a blue background? What would you need to modify to make the turtles make a circle each time?

Lab 8
CSCI 127: Introduction to Computer Science
Hunter College, City University of New York
Fall 2024

Learning Objectives:

Using Python, Gradescope, and Blackboard

Binning Data: Parking Tickets

CSV Data Files

Counting Tickets per Car

Binning Other Data

Top Down Design

Challenges

Lab 8CSCI 127: Introduction to Computer Science Hunter College, City University of New York Fall 2024

Learning Objectives:

Using Python, Gradescope, and Blackboard

Binning Data: Parking Tickets

CSV Data Files

Counting Tickets per Car

Binning Other Data

Top Down Design

Challenges

Lab 8
CSCI 127: Introduction to Computer Science
Hunter College, City University of New York
Fall 2024