Pandas/Python

Question 1

What will the following two slicers return?
1. “owl”[0:2]
2. “hello”[3:]

Answer 1

1. ow
2. lo

Question 2

What is returned by the following statements?

myveg = [‘lettuce’,’celery’,’carrot’]
myveg[1]

Answer 2

celery

Question 3

myveg = [‘lettuce’,’celery’,’carrot’]

Which has the correct syntax to print each element in the list?

Answer 3

for veg in myveg: print(veg)

Question 4

Which statement will add “cauliflower” to the list myveg?

Answer 4

myveg.apend(“cauliflower”)

Question 5

1. What Python data type should you use to store key-value pairs?
2. What Python data type should you use to an ordered sequence of values?

Answer 5

1. dictionary
2. list

Question 6

Which statement will add a new item “mykey” with a value of 3 to the dictionary “mydict”?

Answer 6

mydict[“mykey”] = 3

Question 7

What data type is returned by the following statements: import pandas as pd pd.read_csv(“example1.csv”)

Answer 7

series

Question 8

For pandas variable pd, write a statement that will read from data.txt, a piple delimited file.

Answer 8

pd.read_csv(‘data.txt’, delim=’|’

Question 9

You have a dataframe called df. Which statement will return the first five rows of the dataframe?

Answer 9

df.head()

Question 10

You have a dataframe called df. Which statement will provide some descriptive statistics about the numeric columns in the dataframe?

Answer 10

df.describe()

Question 11

You have a dataframe called “chipo” with a column “quantity”. Which statement will give you the quality column as a series?

Answer 11

chipo[“quality”]

Question 12

What is the OR operator in Python? In Pandas?

Answer 12

Python: OR
Pandas: |

Question 13

You have a dataframe “chipo” with a column called order_id. How can you sort so that the highest value of order_id is shown first, with lower values following?

Answer 13

chipo.sort_values(by=”order_id”,ascending=False)

Question 14

You have a dataframe called miles_per_gallon that lists the car models, their mpg, and origin. Write a panda statement to select the mpg field grouped by origin and ordered by mpg in descending order.

Answer 14

miles_per_gallon.groupby(by=”origin”)[“mpg”].mean().sort_values(ascending=False)

Question 15

You have a dataframe called miles_per_gallon that lists the car models, their mpg, and origin. Write a panda statement to select the 50 records with the lowes mpg values

Answer 15

miles_per_gallon.sort_values(by=’mpg’, ascending=True).head(50)

Question 16

filter your data frame DF to only contain records where the Job field is “admin”

Answer 16

new_df = df[df[“job”] == “admin”]

Question 17

filter your data frame DF to only contain records where the marital column is “married” and the job column is “blue-collar”

Answer 17

marriedblue = df[(df[“marital”] == “married”) & (df[“job”] == “blue-collar”)]

Question 18

filter your data frame DF to only contain records where the marital column is null

Answer 18

nullrecord = df[df[“marital”].isnull() ]

Question 19

What’s the correct syntax for creating a scatter plot in matplotlib?

Answer 19

plt.scatter(x_data, y_data) or
plt.scatter(x_data, y_data, marker=”o”)

Question 20

What is hash table collision and how do you prevent it from happening

Answer 20

[A hash table is a data structure that implements an associative array (ie dictionary) mapping keys to values.]

A hash table collision is the term used to describe a scenario when two or more keys point to the same value.

Some ways to prevent, or significantly minimize, a collision including increasing the size of the table, using a stronger algorithm for your values, and using chaining, or a technique where multiple items that hash to the same location are stored together in a linked list or chain.