Udemy Code Review

Question 1

num = 12 name= Sam

Print ‘My number is 12 and my name is Sam’ in two ways

Answer 1

print(‘My number is {} and my name is {}’.format(num, name)) print(‘My number is {one} and my name is {two}’.format(one=num, two=name))

Question 2

d = {‘k1’:[1,2,3]}

Grab number 2

Answer 2

d[‘k1’][1]

Question 3

What is a set?

set function

Answer 3

A collection of unique elements, eg. {1, 2, 3}

If put in multiples, will return only uniques. e.g. {1, 1, 2, 2, 3, 3} will return {1, 2, 3}

You can pass a list to a set function to get the unique elements:

set([1, 1, 2, 3, 4 ,4, 6, 6])

Returns: {1, 2, 3, 4, 6}

Question 4

Add 5 to this set:

s = {1, 2, 3}

Answer 4

s.add(5)

Question 5

split method

Answer 5

string.split(‘delimiter’)

It splits a string into a list based on the delimiter, which is space by default

e.g.

s = ‘hello my name is Sam’

s.split() returns: [‘hello’, ‘my’, ‘name’, ‘is’, ‘Sam’]

Question 6

Tuple unpacking

x = [(1, 2), (3, 4), (5, 6)]

print 1, 3, 5

Answer 6

for a, b in x:

print(a)

Question 7

numpy equivalent of range function?

Answer 7

np.arange(start, stop, increment)

Question 8

Make an 1x3 array of zeros

Make a 5x5 array of zeros

Answer 8

pass array dimensions as a tuple

np. zeros(3)
np. zeros((5, 5))

Question 9

linspace

Answer 9

np.linspace(start, stop, numberpoints)

Creates an evenly spaced sequence of numbers of desired length (numberpoints)

Question 10

Create a 4x4 identity matrix

Answer 10

np.eye(4)

Question 11

Create 1x5 array with random numbers from uniform distribution

5x5 array same

Answer 11

This returns random numbers between 0 and 1

np. random.rand(5)
np. random.rand(5, 5)

Question 12

Create 2x3 array of random numbers from the normal distribution

Answer 12

np.random.randn(2, 3)

Question 13

Create an array of 10 random integers from 1 to 99

Answer 13

low number is included but high number is not

np. random.randint(1, 100, 10)
np. random.randint(low, high, numberpoints)

Question 14

How do you reshape a 1x25 array into a 5x5 array? Use array ‘arr’

Answer 14

arr.reshape(5, 5)

Question 15

Get the maximum value of the array ‘arr’

Get the minimum value of the array ‘arr’

Get the location of the maximum value of the array ‘arr’

Answer 15

returns index value of max value

arr. max()
arr. min()
arr. argmax()

Question 16

arr = np.arange(0, 11)

slice_of_arr = arr[0:6]

slice_of_arr[:] = 99

What are the elements of arr?

Answer 16

arr = ([99, 99, 99, 99, 99, 99, 6, 7, 8, 9, 10])

Question 17

Pandas is built upon

Answer 17

Numpy

Question 18

What is the difference between pandas series and numpy arrays?

Answer 18

Panda series can use labeled indexes

Question 19

Change my_data into a panda Series with labels as index

labels = [‘a’, ‘b’, ‘c’]

my_data = [10, 20, 30]

Answer 19

Can also pass it a numpy array

pd.Series(data=my_data, index=labels)

Question 20

What is the index when you turn a dictionary into a pandas series?

Answer 20

The index are the keys.

e.g.

d = {‘a’:10, ‘b’:20, ‘c’:30}

pd.Series(d)

returns:

a 10

b 20

c 30

Question 21

USA 1

Germany 2

Italy 5

Japan 4

This is a pandas series ser1. How do you pull out 1?

Answer 21

ser1[index]

ser1[‘USA’]

Question 22

How do you drop a column from a dataframe?

How do you drop a row from a dataframe?

Answer 22

inplace specifies whether to modify original df

df.drop(‘column1’, axis=1, inplace=True)

df.drop(‘row1’, axis=0, inplace=True)

Question 23

How do you do AND and OR conditions with pandas boolean series? e.g. You want the df where df[‘W’] > 0 and df[‘Y’] > 1

Answer 23

You cannot use regular AND or OR operators.

You need to use & or |

e.g.

df[(df[‘W’] > 0) & (df[‘Y’] > 1)]

Question 24

How do you reset the index in a dataframe?

Answer 24

inplace is optional. True means that it will change the original dataframe. Default is False

df.reset_index(inplace=True)

Question 25

How do you set a new index?

Answer 25

inplace = True if want to change original df

df.set_index(column1, inplace=True)

Question 26

drop missing values from a dataframe

Answer 26

axis is optional and default is 0 (rows)

df.dropna(axis=0)

Question 27

How do you fill in missing values in a dataframe?

Answer 27

df.fillna(value= )

Question 28

What is concatenation? How do you concatenate dataframes?

Answer 28

axis=0 concatenates vertically

Combining dataframes

pd.concat([df1, df2, df3], axis = 0)

Question 29

How do you merge dataframes together based on a common column?

Answer 29

similar logic as merging SQL tables together

pd.merge(df1, df2, how=’inner’, on=’commoncolumn’)

Question 30

How do you combine dataframes based on an index?

Answer 30

df1.join(df2)

Question 31

How do you apply a function to a column in a dataframe?

Answer 31

dfd[‘col1’].apply(functionname)

Question 32

How do you drop a column from a dataframe?

Answer 32

df.drop(‘col1’, axis=1, inplace=True)

Question 33

Get a list of the column names of a dataframe

Answer 33

df.columns

Question 34

Sort a dataframe by a column

Answer 34

df.sort_values(by=’col1’)

Question 35

create a pivot table with multiple indexes

Answer 35

df.pivot_table(values=’col1’, index=[‘col2’, ‘col3’], columns=[‘col4’])

Question 36

Figure out working directory

Answer 36

pwd

Question 37

Save a dataframe to a csv

Answer 37

If don’t include index=False, the index is converted into a column

df.to_csv(‘My_output’, index = False)