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.show(3)

Name	Institution	City	County	Enrollment	Founded
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 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, as below?

Name	Founded	Institution	City	County	Enrollment
…	…	…	…	…	…

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
California State Polytechnic University, Humboldt	1913	CSU	Arcata	Humboldt	6025
California State University, Bakersfield	1965	CSU	Bakersfield	Kern	9613
University of California, Berkeley	1869	UC	Berkeley	Alameda	45307
California State University Channel Islands	2002	CSU	Camarillo	Ventura	6128
California State University, Dominguez Hills	1960	CSU	Carson	Los Angeles	16426
California State University, Chico	1887	CSU	Chico	Butte	14183
University of California, Davis	1905	UC	Davis	Yolo	39679
California State University, Fresno	1911	CSU	Fresno	Fresno	23999
California State University, Fullerton	1957	CSU	Fullerton	Orange	40386
California State University, East Bay	1957	CSU	Hayward	Alameda	13673

... (22 rows omitted)

Exercise 3: Filtering

The schools table for reference, if you need it

schools.show(3)

Name	Institution	City	County	Enrollment	Founded
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 rows omitted)

1. How do we get a table with only UC schools?

Show Answer

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

Name	Institution	City	County	Enrollment	Founded
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869
University of California, Davis	UC	Davis	Yolo	39679	1905
University of California, Irvine	UC	Irvine	Orange	35937	1965
University of California, Los Angeles	UC	Los Angeles	Los Angeles	46430	1882
University of California, Merced	UC	Merced	Merced	9110	2005
University of California, Riverside	UC	Riverside	Riverside	26809	1954
University of California, San Diego	UC	San Diego	San Diego	42006	1960
University of California, Santa Barbara	UC	Santa Barbara	Santa Barbara	26420	1891
University of California, Santa Cruz	UC	Santa Cruz	Santa Cruz	19478	1965

2. 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	46430	1882
California State University, Los Angeles	CSU	Los Angeles	Los Angeles	26460	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.show(3)

University	Institution	City	County	Enrollment	Founded
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 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.show(3)

Institution	City	County	Enrollment	Founded	University
CSU	Arcata	Humboldt	6025	1913	California State Polytechnic University, Humboldt
CSU	Bakersfield	Kern	9613	1965	California State University, Bakersfield
UC	Berkeley	Alameda	45307	1869	University of California, Berkeley

... (29 rows omitted)

Questions for you as you read the above code:

1. What methods are being chained together here? Which is executed first, with_column or drop?
2. When is the column method being called?
3. What would happen if you switched the two methods? (try it out)
4. 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
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 rows omitted)

schools = schools.show(4)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[12], 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
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 rows omitted)

University	Institution	City	County	Enrollment	Founded
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869

... (29 rows omitted)

University	Institution	City	County	Enrollment	Founded	Name
California State Polytechnic University, Humboldt	CSU	Arcata	Humboldt	6025	1913	City
California State University, Bakersfield	CSU	Bakersfield	Kern	9613	1965	City
University of California, Berkeley	UC	Berkeley	Alameda	45307	1869	City
California State University Channel Islands	CSU	Camarillo	Ventura	6128	2002	City
California State University, Dominguez Hills	CSU	Carson	Los Angeles	16426	1960	City
California State University, Chico	CSU	Chico	Butte	14183	1887	City
University of California, Davis	UC	Davis	Yolo	39679	1905	City
California State University, Fresno	CSU	Fresno	Fresno	23999	1911	City
California State University, Fullerton	CSU	Fullerton	Orange	40386	1957	City
California State University, East Bay	CSU	Hayward	Alameda	13673	1957	City

... (22 rows omitted)