Table Exercises

We work with the schools table from before.

from datascience import *
import numpy as np

schools = Table.read_table('data/cal_unis.csv')
schools

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882
University of California, Merced	UC	Merced	Merced	8544	2005
University of California, Riverside	UC	Riverside	Riverside	23278	1954
University of California, San Diego	UC	San Diego	San Diego	38798	1960
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	24346	1891
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19700	1965
California State University Maritime Academy	CSU	Vallejo	Solano	1017	1929

... (22 rows omitted)

Pull up the Python Reference and try these exercises yourself! They are roughly in order of increasing difficulty.

Exercise 1: Variable names

How do we get all the column labels of schools?

Show Answer

schools.labels

('Name', 'Institution', 'City', 'County', 'Enrollment', 'Founded')

Exercise 2: Reorder columns

How do we reorder the columns to get the following table?

Hint: use one of select, drop, or with_columns.

Show Answer

schools.select(
  "Name", "Founded",
  "Institution", "City",
  "County", "Enrollment"
)

Name	Founded	Institution	City	County	Enrollment
University of California, Berkeley	1869	UC	Berkeley	Alameda	42519
University of California, Davis	1905	UC	Davis	Yolo	39152
University of California, Irvine	1965	UC	Irvine	Orange	35220
University of California, Los Angeles	1882	UC	Los Angeles	Los Angeles	45428
University of California, Merced	2005	UC	Merced	Merced	8544
University of California, Riverside	1954	UC	Riverside	Riverside	23278
University of California, San Diego	1960	UC	San Diego	San Diego	38798
University of California, Santa Barbara	1891	UC	Santa Barbara	Santa Barbara	24346
University of California, Santa Cruz	1965	UC	Santa Cruz	Santa Cruz	19700
California State University Maritime Academy	1929	CSU	Vallejo	Solano	1017

... (22 rows omitted)

Exercise 3: Filtering

Let’s reset the schools table to our original dataset before continuing.

schools = Table.read_table('data/cal_unis.csv')

The schools table for reference, if you need it

schools

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882
University of California, Merced	UC	Merced	Merced	8544	2005
University of California, Riverside	UC	Riverside	Riverside	23278	1954
University of California, San Diego	UC	San Diego	San Diego	38798	1960
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	24346	1891
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19700	1965
California State University Maritime Academy	CSU	Vallejo	Solano	1017	1929

... (22 rows omitted)

How do we get a table with all of the UC schools?

Show Answer

schools.where("Institution", "UC")

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882
University of California, Merced	UC	Merced	Merced	8544	2005
University of California, Riverside	UC	Riverside	Riverside	23278	1954
University of California, San Diego	UC	San Diego	San Diego	38798	1960
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	24346	1891
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19700	1965

How do we get a table with all the schools in Los Angeles?

Show Answer

schools.where("City", "Los Angeles")

Name	Institution	City	County	Enrollment	Founded
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882
California State University, Los Angeles	CSU	Los Angeles	Los Angeles	27685	1947

Exercise 4: Rename Columns

How do we update schools such that the column Name is renamed University? Hint: Check out the method relabeled.

Show Answer

schools = schools.relabeled("Name", "University")
schools

University	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882
University of California, Merced	UC	Merced	Merced	8544	2005
University of California, Riverside	UC	Riverside	Riverside	23278	1954
University of California, San Diego	UC	San Diego	San Diego	38798	1960
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	24346	1891
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19700	1965
California State University Maritime Academy	CSU	Vallejo	Solano	1017	1929

... (22 rows omitted)

There are many ways to approach a problem. Suppose you didn’t know the method relabeled existed:

Alternate Answer

schools = schools.with_column("University", schools.column("Name")).drop("Name")
schools

Institution	City	County	Enrollment	Founded	University
UC	Berkeley	Alameda	42519	1869	University of California, Berkeley
UC	Davis	Yolo	39152	1905	University of California, Davis
UC	Irvine	Orange	35220	1965	University of California, Irvine
UC	Los Angeles	Los Angeles	45428	1882	University of California, Los Angeles
UC	Merced	Merced	8544	2005	University of California, Merced
UC	Riverside	Riverside	23278	1954	University of California, Riverside
UC	San Diego	San Diego	38798	1960	University of California, San Diego
UC	Santa Barbara	Santa Barbara	24346	1891	University of California, Santa Barbara
UC	Santa Cruz	Santa Cruz	19700	1965	University of California, Santa Cruz
CSU	Vallejo	Solano	1017	1929	California State University Maritime Academy

... (22 rows omitted)

Questions for you as you read the above code:

What methods are being chained together here? Which is executed first, with_column or drop?
When is the column method being called?
What would happen if you switched the two methods? (try it out)
Why is University now the last column?

Exercise 5: Debugging `show`

The following cells exhibit a tricky, but potentially common bug. First, check out the Python Reference to understand what show does.

schools = Table.read_table('data/cal_unis.csv')

schools = schools.show(3)

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965

... (29 rows omitted)

schools = schools.show(4)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[13], line 1
----> 1 schools = schools.show(4)

AttributeError: 'NoneType' object has no attribute 'show'

Like print, show is for display purposes. It does not return anything—i.e., it returns None. The second cell above therefore assigns schools to None!

Despite this, show—just like print—is useful when you want to display intermediate output for debugging purposes.

schools = Table.read_table('data/cal_unis.csv')
schools.show(3) # just the first three rows
schools = schools.relabeled("Name", "University")
schools.show(3) # and again
schools = schools.with_columns("Name", "City")
schools         # the last evaluated value in a cell
                # is displayed by default

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965

... (29 rows omitted)

University	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869
University of California, Davis	UC	Davis	Yolo	39152	1905
University of California, Irvine	UC	Irvine	Orange	35220	1965

... (29 rows omitted)

University	Institution	City	County	Enrollment	Founded	Name
University of California, Berkeley	UC	Berkeley	Alameda	42519	1869	City
University of California, Davis	UC	Davis	Yolo	39152	1905	City
University of California, Irvine	UC	Irvine	Orange	35220	1965	City
University of California, Los Angeles	UC	Los Angeles	Los Angeles	45428	1882	City
University of California, Merced	UC	Merced	Merced	8544	2005	City
University of California, Riverside	UC	Riverside	Riverside	23278	1954	City
University of California, San Diego	UC	San Diego	San Diego	38798	1960	City
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	24346	1891	City
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19700	1965	City
California State University Maritime Academy	CSU	Vallejo	Solano	1017	1929	City

... (22 rows omitted)

Exercise 1: Variable names

Exercise 2: Reorder columns

Exercise 3: Filtering

Exercise 4: Rename Columns

Exercise 5: Debugging show

Exercise 5: Debugging `show`