Schedule for week 1

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

Day 2: Markdown day

Day 3: R and R studio

Day 4: R programming

Day 5: R programming, review and homework