Assignment #2 - List Comprehensions, Classes, CSV, Tabular Data

This assignment consists of three parts:

1. Highest and Lowest Potentially affected vehicles.

2. nelta.py

3. nelta.py and Recalls with Potentially affected vehicles > 500,000

Click on this link: https://classroom.github.com/a/lt0LuChW (https://classroom.github.com/a/lt0LuChW) to accept this assignment in GitHub classroom. This will create your homework respository. Clone your new repository.

Goals

create classes

implement magic methods

      create an iterator

      use list comprehensions

work with csvs

use a lambda function

preview working with tabular data in Python

Part 1 - Highest and Lowest Potentially Affected Vehicles

This part uses a modified dataset from https://www.kaggle.com/datasets/michaelbryantds/automobile-recalls-dataset (https://www.kaggle.com/datasets/michaelbryantds/automobile-recalls-dataset). This data contains Manufacturer name, Recall Type, Component, etc.

The dataset contained in your repository has been modified:

columns have been removed

column names have been changed

some rows have been removed due to non numeric values in numeric columns

some rows have been removed to consider only subset of the data

In recall.ipynb :

1.  do not use external libraries, such as numpy or pandas

2.  you SHOULD use the built-in csv module as the dataset we use has embedded commas

         https://docs.python.org/3/library/csv.html#module-contents

3.  do not use any regular loops ( while , for )

4.  using list comprehensions, dictionary comprehensions and generators is okay (a for within these structures is ok)

5. open the recalls-truncated.csv file

6. display the Manufacturer and Potentially Affected fields for the highest and lowest Potentially Affected in the dataset

         only do this for rows that have vehicle value for the Recall Type column

         your discretion on what to do if there are ties

7. print out your results in any format that you prefer (dict, tuple, str, etc.)

Example output:

# this example prints out the Manufacturer and Potentially Affected as two tuples

('Mercedes-Benz USA, LLC', 1) ('Chrysler (FCA US, LLC)', 1224078)

Part 2 - nelta.py

Background Information

Working with tabular data as a two-dimensional Array is pretty common, but as soon as you try to do some simple operations like filtering based on column name, things get complicated quickly unless you throw in some additional libraries or tools.

In this homework, we'll being creating (a maybe over-engineered) module for reading in csvs and filtering rows based on column values. You'll have to use some Python features in your implementation, like __iter__ , list comprehensions, etc.

For example, imagine we had a csv containing people's names, the number of fruits they eat weekly, and their favorite color (um… idk?). This data is in a csv called fruitarians.csv , and can be visualized as a table (note that row # is not in the csv):

row # first last weekly_fruits_eaten fav_color

0 abe apple 0 red

1 bob banana 4 yellow

2 carol coconut 100 white

3 bob blueberry 9 blue

4 eve endive 20 green

5 frances fruit 5 ?

6 ann apple 23 green

What if we'd like to run some reports on this? For example:

read in the csv…

what do the first three columns look like?

how many people have the last name, apple?

what is the first name and number of fruits eaten / week of everyone that eats more than 10 fruits a week

how many people have a first name less than 4 letters eat less than 10 fruit / week?

We'll create a module to do this… and it'll look something like this:

import nelta as nt

# read in the csv

t = nt.read_csv('fruitarians.csv')

# what do the first three columns look like?

t.head(3)

"""

first last weekly_fruits_eaten fav_color

0 abe apple 0.0 red

1 bob banana 4.0 yellow

2 carol coconut 100.0 white

"""

# how many people have the last name, apple?

t[t['last'] == 'apple'].shape()[0]

"""

2

"""

# what is the first name and number of fruits eaten / week of everyone that eats more than 10 fruits a week

t[t['weekly_fruits_eaten'] > 10][['first', 'weekly_fruits_eaten']]

"""

first weekly_fruits_eaten

2 carol 100.0

4 eve 20.0

6 ann 23.0

"""

# how many people have a first name less than 4 letters eat less than 10 fruit / week?

def length_less_than(n):

def is_length_less_than_n(s):

return len(s) < n

return is_length_less_than_n

first_name_three = t[t['first'].map(length_less_than(4))]

first_name_three[first_name_three['weekly_fruits_eaten'] < 10]

"""

first last weekly_fruits_eaten fav_color

0 abe apple 0.0 red

1 bob banana 4.0 yellow

3 bob blueberry 9.0 blue

"""

Instructions

1. You'll be modifying two classes:

LabeledList - kind of like a dict , but ordered, allows vectorized operations, and iterates over values instead of keys

This is already partially implemented!

You'll only need to add missing methods

Table - a table of data with column labels

2. Open nelta.py in a text editor of your choice

3. When writing code for the classes mentioned above…

YOU MUST USE AT LEAST 4 LIST COMPREHENSIONS!

YOU CANNOT USE THE FOLLOWING MODULES: numpy , pandas

YOU SHOULD use the built-in csv module

4. Using your previously implemented nelta.py as a module, import it and use it in a notebook to do some very simple data analysis!

LabeledList

A LabeledList acts like a dictionary… but:

it's ordered (note that 3.7 and greater has ordered dictionaries by default, though)

when you loop over it, you get values instead of keys

if you use a comparison operator with it… and a scalar value (a number, for example), that comparison is done on each value, yielding a new LabeledList composed of only bool values

duplicate 'keys' are allowed

Here's how you might use it:

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

ll['A'] # gives back value at label 'A'

ll['BB'] # gives back new LabeledList composed of labels 'BB' and their values

ll[['A', 'D', 'BB', 'BB']] # gives back new LabeledList composed of the labels specified in list... along wit

h their values

ll > 2 # gives back a new LabeledList composed of labels in original, along with boolean results of compariso

n

Implementation:

several properties / methods for this class are already implemented (see specs below)

you'll only need to write the following (again, see specs below):

__iter__

__gt__

__eq__

__ne__

__lt__

map

Properties:

Already Implemented

self.values - contains the values in this LabeledList as a list

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

ll.values # [1, 2, 3, 4, 5]

self.index - contains the labels in this LabeledList as a list

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

ll.index # ['A', 'BB', 'BB', 'CCC', 'D']

__init__(self, data=None, index=None)

Already Implemented

Creates a new LabeledList .

data - the values stored in self.values ; represents all of the values in this LabeledList

index - the labels associated with each value data and index are assumed to be the same length (no error checking is necessary) and the order of the elements in each list determines which values are associated with which labels (if data is [0, 1] and values are ['foo', 'bar'] , then the label 0 is associated with the value 'foo'

You can assume that the labels and values are only str , int , float , and bool (no type checking is needed in the constructor). Duplicate labels are allowed.

Note that if index is None then the labels should be from 0 to the length of the data - 1:

list_with_default_labels = nt.LabeledList(['foo', 'bar', 'baz'])

"""

0 foo

1 bar

2 baz

"""

list.index # [0, 1, 2]

However, if index is provided…

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

"""

A 1

BB 2

BB 3

CCC 4

D 5

"""

__str__(self) and __repr__(self)

Already Implemented

These two methods will give the string representation of a Labeled List . __str__ is used for human readable format (such as when printing) and __repr__ is used for displaying what the object actually is (for example, debugging by just typing the object name in the interactive shell).

For our purposes, these will return the same string (in fact, one can call the other).

The string should be a tabular format where labels are on the left and values on the right. You can space this out any way you like, as long as it's very clear what the labels and columns are.

Using the earlier example, here's a nicely formatted LabeledList :

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

"""

A 1

BB 2

BB 3

CCC 4

D 5

"""

It will be useful to use dynamically padded strings to maintain consistent widths for columns. This can be done with format strings and the format specification mini language (https://docs.python.org/3/library/string.html#format-specification-mini-language).

For example:

s = 'foo'

# print out 'foo' so that it's padded with spaces and tis total length is 10

print(f'{s:>10})

# results in:

# foo

The : signals that a format specifier is coming up. The > aligns right. Finally, the 10 is the total width of the new string (spaces will pad the left side).

Of course, you may want the 10 to be variable…

vals_max_len = m # imagine that this is the length of the longest label

label = s # imagine that this is a label whose length is shorter than the longest label

# we want to pad this thing ^^^^

# create a format specifier that right justifies and pads

format_spec = f'>{vals_max_len}'

# now add that format specifier to another formatted string by nesting curly braces!?

f'{label:{format_spec}}'

Note that if the variable in the format string is a boolean and a format specifier is given, then the boolean will either be a 0 or 1 rather than True or False which is ok for our purposes (a work-around is to convert the boolean to a string first… then format with f'' )

do your best to have dynamic widths, but grading will be generous for this feature

__getitem__(self, key_list)

Already Implemented

__getitem__ allows our object to be indexed / 'keyed' into as if it were a dict . In LabeledList the label is the key. Our implementation's key behavior. depends on the type of the key:

1. if the key is another LabeledList then the key is the values property of that labeled list (which is, of course a list … see below for how to handle list and a list of only bool values)

2. if the key is a list , then that means that we're retrieving multiple labels and values, so a new LabeledList is returned with each label specified and its associated value (if a label occurs more than once, add all occurrences)

3. if the key is specifically a list of bool values, then give back a new LabeledList where the only label and value pairs given are the ones where the position matches the position of a True in the incoming key list (you can assume that the list of bool values must be the same length as the index of labels… you can error handling if it makes it easier to debug your code, though!)

4. given any single value as the label (such as str , int )… you will get back: a. the value associated with that exact label if the label occurs only once b. a new LabeledList composed of that label repeated, along with its values

Ok. So that's pretty confusing. Here are some examples:

ll = nt.LabeledList([1, 2, 3, 4, 5], ['A', 'BB', 'BB', 'CCC', 'D'])

# 1 (values are taken from LabeledList as a list...

# more than one label yields all label and value pairs)

ll[nt.LabeledList(['A', 'BB'])]

"""

A 1

BB 2

BB 3

"""

# 2 (same as above, but with plain list)

ll[['A', 'BB']]

"""

A 1

BB 2

BB 3

"""

# 3 (only the last two label value pairs have the same positions as True

ll[[False, False, False, True, True]]

"""

CCC 4

D 5

"""

# 4a (value is returned as is... just like a dict)

ll['A']

"""

1

"""

# 4b (new LabeledList is returned even though only single value key)

ll['BB'] #

"""

BB 2

BB 3

"""

Use the built-in function, isinstance (https://docs.python.org/3/library/functions.html#isinstance) to check if a value is a particular type:

isinstance(key_list, LabeledList)

isinstance(key_list, list)

__iter__(self)

Implement __iter__ so that it returns a new object that has a __next__ method. Since self.values is a list, you can return the result of calling the built-in function iter with self.values as the argument.

# using the previous version of ll

for val in ll:

print(val)

"""

1

2

3

4

5

"""

__eq__(self, scalar) , __ne__(self, scalar) , __gt__(self, scalar) , __lt__(self, scalar)

These methods all correspond to an associated comparison operator ( == , > , etc.). They should return a new LabeledList of bool values corresponding to the operation specified for every value compared to the scalar passed in.

if the value being compared to the scalar is None , return False .

although the parameter name is scalar , you can let this work with any compatible types

you don't have to deal with any TypeError s (just let them occur)

if there is an index present, keep that index

this might be a good place to get in your four list comprehensions

# compares every element in the labeled list to 2 using >

nt.LabeledList([0, 1, 2, 3, 4]) > 2

0 False

1 False

2 False

3 True

4 True

# compares every element in the labeled list to 1 using ==

ll = nt.LabeledList([1, 2], ['x', 'y'])

ll == 1

x True

y False

# note that you can allow these operations to work on different types

# here, we have strings compared with ==

nt.LabeledList(['a', 'b', 'c', 'b', 'b']) == 'b'

0 False

1 True

2 False

3 True

4 True

# if a value in the labeled list is None, then always return False

nt.LabeledList([None, 0, 2]) > 1

0 False

1 False

2 True

map(self, f)

Gives back a new LabeledList with all of the values transformed to the result of calling f on that value.

def squared(n):

return n ** 2

nt.LabeledList([5, 6, 7]).map(squared)

0 25

1 36

2 49

Table

A Table represents tabular data with row labels ( index ) and column names ( columns )… along with 2 dimensional grid of data

( data ).

It supports operations for filtering by values in a column… as well as selecting specific columns.

Properties

self.values - contains the values in this Table as a list

t = Table([[1, 2, 3],[4, 5, 6]],['a', 'b'], ['x', 'y', 'z'])

.values # [[1, 2, 3],[4, 5, 6]]

self.index - contains the row labels in this Table as a list

t = Table([[1, 2, 3],[4, 5, 6]],['a', 'b'], ['x', 'y', 'z'])

t.index # ['a', 'b']

self.columns - contains the column names in this Tabled as a list

t = Table([[1, 2, 3],[4, 5, 6]],['a', 'b'], ['x', 'y', 'z'])

t.index # ['x', 'y', 'z']

__init__(self, data, index=None, columns=None)

If either index or columns are not included, then default to numeric values from 0 up to length of index - 1 or columns - 1

t = Table([['foo', 'bar', 'baz'],['qux', 'quxx', 'corge']])

0 1 2

0 foo bar baz

1 qux quxx corge

Otherwise, adding the index and columns as arguments will explicitly set the row labels and column names

t = Table(d, ['foo', 'bar', 'bazzy', 'qux', 'quxx'], ['a', 'b', 'c', 'd', 'e'])

a b c d e

foo 1000 10 100 1 1.0

bar 200 2 2.0 2000 20

bazzy 3 300 3000 3.0 30

qux 40 4000 4.0 400 4

quxx 7 8 6 3 41

__str__(self) and __repr__(self)

Again, these two methods will give the string representation of an object. __str__ is used for a human readable format (for example, used with print ), and __repr__ is used for displaying what the object actually is (for example, typing the object name Jupyter). Both of these methods return strings, and for our purposes, these can be the same string.

For a Table object, create a string representation in any way such that rows and columns can be clearly distinguished. See the example below for a potential format (it's ultimately up to you how you'd like to format it, though… as long as the grader can read it and determine which rows and columns are aligned).

Please read the notes for the LabeledList __str__ and __reper__ methods for info on setting a consistent width for cells using string formatting ( f'{foo:{format_spec}}' ).

t = Table([['foo', 'bar', 'baz'],['qux', 'quxx', 'corge']])

0 1 2

0 foo bar baz

1 qux quxx corge

__getitem__(self, col_list)

__getitem__ allows our Table to be indexed / 'keyed' into as if it were a dict . The behavior. of indexing or retrieving by key depends on the type of the value used as a key!

Essentially, most keys result in selecting all rows, but specifying which columns to include in a new Table (for example t['a'] selects column a from all rows, and t[['a', 'b']] selects column a and b from all rows. The main exception is a list or LabeledList of bool values… which specifies which rows to include based on position of the bool value and the position of the row (for example, if t has 2 rows, then t[[True, False]] will only give back the first row as a new Table .

If there's ever only one column returned, give back a LabeledList . Otherwise, give back a Table .

For exact details, see below:

1. if the key is a LabeledList , then the key is the values property of that labeled list (which is a list )… and a Table consisting of only the columns contained in the LabeledList is returned (note that all rows are returned) … note that if the LabeledList values are all bool , then follow the procedure for dealing with a list of bool values as shown below

2. if the key is a list , then that means that we're retrieving multiple columns, so a new Table is returned including only the columns specified by the elements in the key list passed in. If a key list has repeated column names, duplicate the column. If a column name matches more than one column, add both columns in the resulting Table.

3. if the key is specifically a list of bool values, then give back a new Table where the only rows given are the ones where the position matches the position of a True in the incoming key list (you can assume that the list of bool values must be the same length as the total number of rows in the Table object)

4. given any single value as the label (such as str , int )… you will get back: a. that column for all rows as a LabeledList if there is only one occurrence of that column name b. a new Table composed of that column repeated if there are duplicate column names

Once again, the behavior. is complex enough to warrant examples:

#####

# Remember... if only one column is given back, return a LabeledList

# ...but if there's more than one column, give back a Table

#####

# 1 (using a LabeledList to select columns)

t = Table(d, ['foo', 'bar', 'bazzy', 'qux', 'quxx'], ['a', 'b', 'c', 'd', 'e'])

t[LabeledList(['a', 'b'])]

"""

a b

foo 1000 10

bar 200 2

bazzy 3 300

qux 40 4000

quxx 7 8

"""

# 2 (the first two columns are selected using a list of columns...

# notice that repeat columns are allowed)

t = Table([[15, 17, 19], [14, 16, 18]], columns=['x', 'y', 'z'])

t[['x', 'x', 'y']]

"""

x x y

0 15 15 17

1 14 14 16

"""

# 3 (select only the first and third rows by using a list of booleans)

t = Table([[1, 2, 3], [4, 5, 6], [7, 8 , 9]], columns=['x', 'y', 'z'])

t[[True, False, True]]

"""

x y z

0 1 2 3

2 7 8 9

"""

# 4a (using a column name that matches only a single column gives

# back a LabeledList... note no column names, but there are labels!)

t = Table([[1, 2, 3], [4, 5, 6]], columns=['a', 'b', 'a'])

t['b']

"""

0 2

1 5

"""

# 4b (however, if more than one column matches column name, include

# all matched columns in the resulting Table object)

t = Table([[1, 2, 3], [4, 5, 6]], columns=['a', 'b', 'a'])

t['a']

"""

a a

0 1 3

1 4 6

"""

head(self, n) and tail(self, n)

Returns a Table showing the first or last n row respectively.

t = Table([[1, 2], [3, 4], [5, 6], [7, 8]], columns=['x', 'y'])

print(t.head(2))

"""

x y

0 1 2

1 3 4

"""

print(t.tail(2))

"""

x y

2 5 6

3 7 8

"""

shape(self)

Gives back a tuple containing the number of rows and columns:

t = Table([[1, 2], [3, 4], [5, 6], [7, 8]], columns=['x', 'y'])

t.shape()

"""

(4, 2)

"""

read_csv(fn)

Finally, in nelta.py , write a function that reads in a csv file and gives back a Table object:

1. assume that the first row is the header (it can be treated as column names)

2. there can be commas embedded in the actual data, so you'll have to use the built in csv module

3. convert numeric values to floats (use try / except … and look for ValueError specifically)

when creating a Table object, use a generated auto-incrementing index (do not use the first column as the index… as in the example of the fruitarians.csv file where "row" is not actually included in the file)

To test your code, you can try to open a csv from your nelta.py module. Once you're finished testing, you can comment out the code (or alternatively, you can wrap your test code in if __name__ == '__main__': to only run it when the module isn't being imported)