R Programming Quiz 1 (Week 1) John Hopkins Data Science Specialization Coursera for the github repo https://github.com/mGalarnyk/datasciencecoursera

quiz1.md

R Programming Quiz 1 (JHU) Coursera

github repo for rest of specialization: Data Science Coursera

Question 1

R was developed by statisticians working at...

Answer

The University of Auckland

Question 2

The definition of free software consists of four freedoms (freedoms 0 through 3). Which of the following is NOT one of the freedoms that are part of the definition?

Answer

The freedom to sell the software for any price.

Question 3

In R the following are all atomic data types EXCEPT

Answer

matrix

Question 4

If I execute the expression x <- 4 in R, what is the class of the object 'x' as determined by the `class()' function?

Answer

numeric

x <- 4
class(x)

Question 5

What is the class of the object defined by x <- c(4, TRUE)?

Answer

numeric

x <- c(4, TRUE)
class(x)

Question 6

If I have two vectors x <- c(1,3, 5) and y <- c(3, 2, 10), what is produced by the expression cbind(x, y)?

Answer

a 3 by 2 numeric matrix

x <- c(1,3, 5)
y <- c(3, 2, 10)
cbind(x, y)

Question 7

A key property of vectors in R is that

Answer

elements of a vector all must be of the same class

Question 8

Suppose I have a list defined as x <- list(2, "a", "b", TRUE). What does x[[1]] give me?

Answer

a numeric vector containing the element 2

x <- list(2, "a", "b", TRUE)
x[[1]]

class(x[[1]])

Question 9

Suppose I have a vector x <- 1:4 and a vector y <- 2. What is produced by the expression x + y?

Answer

a numeric vector with elements 3, 4, 5, 6.

x <- 1:4
y <- 2
x + y

class(x + y)

Question 10

Suppose I have a vector x <- c(17, 14, 4, 5, 13, 12, 10) and I want to set all elements of this vector that are greater than 10 to be equal to 4. What R code achieves this?

Answer

x[x >= 11] <- 4

x <- c(17, 14, 4, 5, 13, 12, 10)
x[x >= 11] <- 4
x

Question 11

In the dataset provided for this Quiz, what are the column names of the dataset?

Answer

Ozone, Solar.R, Wind, Temp, Month, Day

# install package if doesnt exist 
install.packages("data.table")
library("data.table")

# Reading in data
quiz_data <- fread('hw1_data.csv')

# Column names of the dataset 
names(quiz_data)

Question 12

Extract the first 2 rows of the data frame and print them to the console. What does the output look like?

Answer

  Ozone Solar.R Wind Temp Month Day
1    41     190  7.4   67     5   1
2    36     118  8.0   72     5   2

# First two rows 
quiz_data[c(1,2)]

Question 13

How many observations (i.e. rows) are in this data frame?

Answer

153

nrows(quiz_data)

Question 14

Extract the last 2 rows of the data frame and print them to the console. What does the output look like?

Answer

   Ozone Solar.R Wind Temp Month Day
152    18     131  8.0   76     9  29
153    20     223 11.5   68     9  30

tail(quiz_data, 2)

Question 15

What is the value of Ozone in the 47th row?

Answer

21

quiz_data[47, Ozone]

Question 16

How many missing values are in the Ozone column of this data frame?

Answer

37

# Going back to data.frame because dont it hasnt been taught yet in this specialization
hw1 = read.csv('hw1_data.csv')
sub = subset(quiz_data, is.na(Ozone))
nrow(sub)

# Can also remmove Missing Values using Something like This
quiz_data[complete.cases(quiz_data),]

Question 17

What is the mean of the Ozone column in this dataset? Exclude missing values (coded as NA) from this calculation.

Answer

42.1

Explanation

The 'mean' function can be used to calculate the mean.

hw1 = read.csv('hw1_data.csv')
sub = subset(hw1, !is.na(Ozone), select = Ozone)
apply(sub, 2, mean) 

Question 18

Extract the subset of rows of the data frame where Ozone values are above 31 and Temp values are above 90. What is the mean of Solar.R in this subset?

Answer

212.8

quiz_data = read.csv('hw1_data.csv')
sub = subset(quiz_data, Ozone > 31 & Temp > 90, select = Solar.R)
apply(sub, 2, mean)

Question 19

What is the mean of "Temp" when "Month" is equal to 6?

Answer

79.1

Explanation

quiz_data = read.csv('hw1_data.csv')
sub = subset(hw1, Month == 6, select = Temp)
apply(sub, 2, mean)

Question 20

What was the maximum ozone value in the month of May (i.e. Month = 5)?

Answer

115

Explantion

quiz_data = read.csv('hw1_data.csv')
sub = subset(quiz_data, Month == 5 & !is.na(Ozone), select = Ozone)
apply(sub, 2, max)

Thanks for this, so helpful. The course didn't go through a lot of the above code

Thank you so much for your help

Incredibly helpful

Thanks for your help, the 2nd part is not covered in the lecture

Thanks for the help. I went through the coursework twice but couldnt find how to do operations on the columns of the tables, This was very helpful!

Thanks for the help

coding part is right but not all

Thanks my friend!

thank you so much

Very Helpful and kinda new commands for me, Thank you.

Thank you!

thank u so much .
some of the questions in the quiz require code that hasn't been taught yet in the course

Very helpful... thank u very much...!

Thank you very much for this help.
You really contributed to my pass mark.
Thanks

A big help to all who don't wanna buy the course but still want to learn.

apply(sub, 2, max) what does the 2 represent in this?

I'm not entirely sure how to use the "apply" function yet, but I was able to get the same answers using commands like >mean(sub$Temp) after creating the subset correctly. The course doesn't go over the correct format for subsetting data very well so this quiz was really hard!

Thank you so much. This quiz was hard.

Rating, Cocoa.Percent, and Company.Location. You decide to use the select() function to create a new data frame with only these three variables.

Assume the first part of your code is:

trimmed_flavors_df <- flavors_df %>%

Add the code chunk that lets you select the three variables.

Assume the first part of your code is:

trimmed_flavors_df %>%

You want to use the summarize() and mean() functions to find the mean rating for your data. Add the code chunk that lets you find the mean value for the variable Rating.

This came in so clutch. Thank you sir.

I was so confused, looking everywhere, going back on the book and lessons, until I had to look for this! thank you, you saved the day, I was going bananas!!

Thank you for helping me out in my assignment. I initially panic since the question answer were not there in videos.

thank youuu, this quiz was way tooo long lol