Chapter 8

Question 1

What is a set and what can you put in it?

Answer 1

A set is a mutable container of UNORDERED elements (no indices) that are unique (no duplicates).

Created using the set() function.

Holds sequence-type iterable objects (i.e. lists, tuples, strings)

Question 2

How do you make a set literal?
How do you make an empty set?

Answer 2

set{}
set()

Question 3

In a set, the index operator…

Answer 3

…is not valid, because a set contains unique unordered elements with no set position.

Question 4

A set is often used to…

Answer 4

…reduce a list of items that potentially contains duplicates into a collection of unique values

Question 5

How can you remove duplicates from a list?

Answer 5

Pass the list into a set() to make it into a set of unique values
Format:
ex_list = []
unique_set = set(ex_list)
#copies ex_list to unique_set w/o duplicates

Question 6

Are sets mutable or immutable?

Answer 6

Mutable

Question 7

How do you add elements to a set?
How do you remove elements?
What does the .pop function do?

Answer 7

set.add(value)
set.remove(value)
set.pop() removes a random element

Question 8

How would you add the elements of set_2 to set_1?
How would you clear ALL values in a set?

Answer 8

set1.update(set_2)
set.clear()

Question 9

This function returns a set containing the common elements shared between set and all provided sets

Answer 9

set.intersection(set_a, set_b, set_c, …)

Question 10

This function returns a set containing all the unique elements in all given sets.

Answer 10

set.union(set_a, set_b, set_c, …)

Question 11

Function that returns a set containing only the values in set that are not found in the given argument sets.

Answer 11

set.difference(set_a, set_b, set_c, …)

Question 12

Function that returns a set containing only values found in exactly one of either set_a or set_b

Answer 12

set_a.symetric_difference(set_b)

Question 13

What is a dictionary?
What is the object type?
What is its mutability?

Answer 13

A dictionary is a container used to associate/map keys (terms placed in a dict) with values.

Represented by object type dict

Dictionaries are mutable.

Question 14

What is a key?
What types can be used for a key?

Answer 14

A key is a term that can be located in a dictionary, (such as the word “cat” in the English dictionary), and is associated with a value through the dict.

A key can consist of any immutable type (string, tuple, etc.), the value can be of any type.

Question 15

What is the syntax for creating a dictionary?

Answer 15

ex_dict =
{
“Example Key 1” : 77
“Example Key 2” : 86
}

Question 16

What will cause a KeyError when calling an item in a dictionary?
How do you avoid this?

Answer 16

Dictionary elements cannot be indexed, and thus accessing entries by indexing will result in a KeyError.

We avoid this by putting the key itself in brackets where an index would normally be located when accessing.

Question 17

Are elements in a dictionary ordered or unordered?

Answer 17

Dictionary elements are ordered, despite the fact that they cannot be indexed.

Question 18

How do you add or modify an entry in a dictionary?

Answer 18

adds key “ex_key” and assigns value “ex_val”

ex_dict[ex_key] = ex_val

Question 19

How do you delete an entry from a dictionary?

Answer 19

deletes key “ex_key” from dictionary “dict”

del ex_dict[ex_key]

Question 20

What does the sort() function do?
What rules does it follow?

Answer 20

sort() re-arranges the elements of a list from lowest value to highest.

Numbers are sorted by value, strings are sorted according to ASCII/Unicode values, lists are compared element by element, etc.

Question 21

What does the sorted() function do?
How does this differ from the sort() function?

Answer 21

sorted() sorts the elements the same as list.sort(), but returns the elements as a new list rather than rearranging the elements of the existing list.

Question 22

What is the purpose of the optional key argument in the list.sort() and sorted() functions?

Answer 22

The key argument specifies a function to be applied to each element prior to comparing their values.

For example, “key=str.lower” as the key argument will convert all elements to lower case before comparing their values.

Question 23

When using list.sort() or sorted(), how would you reverse the resulting list of elements?

Answer 23

Use the optional argument: reverse=True

Question 24

What are the 2 primary ways to create a dict?

Answer 24

1). Wrap curly braces { } around key-value pairs (whether literals or variables).
i.e.: {‘Jose’: ‘A+’, ‘Gino’: ‘C-‘}
2). Use the dict function
i.e.: dict(Bob=’97’, John=’83’)

Question 25

How do you test for the existence of a key in a dictionary?

Answer 25

ex_key in ex_dict

Question 26

What is a hash?
Why does this matter in the context of dictionaries?

Answer 26

A hash is a transformation of a key into a unique value that allows the interpreter to perform fast lookup.

When using a loop to iterate through a dictionary, the order in which elements are evaluated is according to their hash value, not necessarily the order they’re placed in the dictionary.

Question 27

What is a view object?

Answer 27

A view object provides read-only access to dictionary keys and values (in real time).

A program can iterate over a view object to access key-value pairs in a dictionary one at a time.

Question 28

This function returns a view object that yields a tuple of key-value pairs from a dict.

Answer 28

dict.items()

Question 29

This function returns a view object that yields keys from a dict.

Answer 29

dict.keys()

Question 30

This function returns a view object that yields values from a dict.

Answer 30

dict.values()

Question 31

What is a nested dictionary?
How many layers of nesting can you have?

Answer 31

When a dictionary contains another dictionary as one of its values.

There is no limit.

Question 32

What is a data structure?

Answer 32

A data structure is a method of organizing data in a logical and coherent fashion.

Question 33

What is NumPy?

Answer 33

NumPy is a package that provides tools for mathematical computations, frequently used in data science and statistical analysis.

Question 34

What is an array? How does it differ from other data types we have learned about?

Answer 34

It is an object that is conceptually similar to a list, with the added benefit of more mathematical support and performing mathematical operations faster.

Question 35

What is ndarray

Answer 35

ndarray is the numpy array data type, where the nd stands for ‘n’-dimentional, and ‘n’ can be any number of dimensions.

Question 36

How do dimensions work in arrays? (i.e. how does the structure of an array change with each additional dimension?)

Answer 36

An “N”-dimensional array has “N” levels of nested containers.
At each level, every container must have the same number of elements.
The shape of an array is a tuple of the lengths of each of its dimensions.
The size of an array is the total number of elements.

Question 37

In a 2D array, the 0-axis runs along…

Answer 37

…the array’s rows

Question 38

True or False: arrays are mutable and their shapes can be changed.

Answer 38

False

While arrays are mutable, their shapes cannot be changed after creation.

Question 39

This function returns an ndarray based on a given object, like a list.

Answer 39

array(object)

Question 40

These functions each return an ndarray of a specified shape filled with zeros, ones, or a specified value.

Answer 40

zeros(array_shape)
one(array_shape)
full(arr_shape, value)

Question 41

This function returns the element located at indices [row_index, col_index].

Answer 41

array[row_index, col_index]

Question 42

This function returns a new ndarray with a row or column deleted from the given ndarray.

Answer 42

delete(ndarray, index, axis)

Deletes row or col indicated by the index. If axis = 0, delete row. If axis = 1, delete column.

Question 43

This function sorts an ndarray in place in ascending order along an axis. If axis=None, the array is flattened into a 1D array, then sorted. If no argument is passed, sorting occurs along the last axis.

Answer 43

ndarray.sort(axis)

Question 44

This function returns a flattened (1D) version of the given ndarray.

Answer 44

ndarray.ravel()

Question 45

This function returns a new ndarray containing the elements of the given ndarray with a new shape

Answer 45

ndarray.reshape(new_shape)