Homework

I will list the homework at the begining of each weekly schedule, so that you have a better idea of what you need to do.

For the homework, you need to submit two files: a markdown file named homework1.md, and an R file named homework1.R.

In homework1.md, answer following questions:

1. What Markdown editor did you choose, and why?
2. Write a summary of what you learned this week, using markdown. Name the file homework1.md. Using different type of fonts, and ordered/unordered list.

In homework1.R:

Write R program to do the following. NOTE: if you haven’t learned, the functions for computing sum and mean of vector/matrix is sum and mean. Look at their function helps if needed.

1. Compute the sum and mean of integers from 1 to 10.

2. Create a vector of 5 elements, you can put in some random numbers in the vector. Take out the 2nd to 4th elements, and compute their sum and mean.

3. Create a vector of 5 elements, you can put in some random numbers in the vector. Take out the 2nd and 4th elements, and compute their sum and mean.

4. Create a 3x3 matrix, you can put in some random numbers in the matrix. Compute the sum and mean of each row and column.

5. Create two vectors, each with 3 elements. Compute the sum and difference of each element in the vector.

6. Create two vectors, each with 3 elements, combine them into one vector of 6 elements.

7. Create two vectors, each with 3 elements, (1) combine them into a 2x3 matrix; (2) combine them into a 3x2 matrix.

8. Run following code to create a string: string = "This is a string"

   • How many characters are there in the string?
   • Return the first 10 characters in the string.
   • how many words are there in the string?
   • Return the first two words in the string.
   • Replace This by That in the string.
   • Remove all spaces in the string.

9. Run following code to create a vector of strings sample(c("car", "truck", "plane"), 100, replace=TRUE)

   • Convert the string vector to factors.
   • How many levels are there in the factor?
   • How many items are there for each level?
   • Replace all car by bike in the vector, by changing the level of the factor.
   • After above step, change the factor back to string vector. See what you get.
     

10. Initialize the vector x using the following commands. Present a one line R statement that will count the total numbers that are evenly divisible by 15 and 25. The answer will be a single number.

    set.seed(222)
    x = floor(rnorm(300, 200, 90))

11. Given the following vector provide a one line command that computes the sum of all element values that are within 5 of the maximum number of this vector. The correct answer is 599.0835. You must present a one line R statement that issues this response. Hint, using the absolute function will be useful.

    set.seed(123)
    x = rnorm(100, 100, 10)

    ---

Extra practices

Vector and matrix indexing

1. Create a 4x3 matrix, you can put in some random numbers in the matrix (for example, simply use 1 to 12).
   • Return the first and third row
   • Return the first and second column
   • Return a submatrix containing the first and third row and the first and second column.
2. seq is a useful function to create a sequence of numbers in a vector. Read the function help for seq.
   • Create a sequence of even numbers from 1 to 50.
     
   • Create a sequence of add numbers from 1 to 50.

Comparison

Read the section for logical operators again at https://www.guru99.com/r-data-types-operator.html#5. Note, R has ability to compare a vector or matrix to a single element. In that case, each elemenet in the vector or matrix will be compared to the single element, and the return will be a logical vector/matrix.

1. How many numbers in 1:100 can be evenly divided by 3?

2. The comparison can be performed on characters too. Run following code to create a vector of strings sample(c("car", "truck", "plane"), 100, replace=TRUE)

   • How many items are “car” in this vector of string?
   • How many items are NOT “truck” in this vector of string?

3. How many numbers in 1:100 are greater than 20?

4. How many numbers in 1:100 are greater than 20 AND smaller than 50?

5. How many numbers in 1:100 are smaller than 20 OR or greater than 50?

Combination of comparison and indexing

Use a combination of comparison and indexing can extract uesful information from a large dataset. Here let’s do something a little interesting. I obtained the career regular season statistics for Shaquille O’Neal. You can read them into R using

shaqStat = read.csv("http://www.haowulab.org/DataSummerCamp/data/shaqStat.csv")

What you read in is a data frame, similar to a matrix. We will learn it next week. Take a look at shaqStat in R. Let’s do some simple practice

• Return the statistics for Shaq when he played at ORL.
• Return the following statistics for Shaq when he plays at ORL: G, FG, FGA
• Can you compute the overall FG% when Shaq played at Orlando?
• Repeat the above, but only for the statsitics when Shaq played at LAL.

Day 1: R and R studio

• Read https://www.guru99.com/r-programming-introduction-basics.html.
• Install R and Rstuido, following http://www.sthda.com/english/wiki/installing-r-and-rstudio-easy-r-programming. And watch https://www.youtube.com/watch?v=lVKMsaWju8w.
• Play with Rstudio to get to know the menu items.

Day 2: Markdown day

• Install a Markdown editor. I use MacDown on Mac, not sure about on Windows. Do some search, try different ones, and pick the one your like.
• Watch https://www.youtube.com/watch?v=6A5EpqqDOdk for markdown.
• Start to learn markdown at https://www.markdowntutorial.com/.
• Write a simple markdown document.

Day 3: R and R studio

• Understand the “directory” on computer. Setup your R working directory by reading http://www.sthda.com/english/wiki/running-rstudio-and-setting-up-your-working-directory-easy-r-programming.
• Start to learn R programming language: https://www.guru99.com/r-data-types-operator.html. Play the examples in R by copying/pasting the command into R and see the results.
• Learn how to get function helps in R by reading http://www.sthda.com/english/wiki/getting-help-with-functions-in-r-programming.

Day 4: R programming

• Understand the concept of matrix. If you don’t know it, google “matrix” and look it up.
• Learn R matrix at https://www.guru99.com/r-matrix-tutorial.html.
• Watch the first quarter of https://www.youtube.com/watch?v=lL0s1coNtRk.
• Under stand R characters: read http://www.r-tutor.com/r-introduction/basic-data-types/character, and https://data-flair.training/blogs/r-string-manipulation/.

Day 5: R programming, review and homework

• Understand factors: read http://www.sthda.com/english/wiki/easy-r-programming-basics#factors, and https://www.guru99.com/r-factor-categorical-continuous.html.
• Review all materials learned this week.
• Do homework.