Description

Download and install the latest version of R and R Studio.

Problem 1. When you open R Studio, go to the text editor in the top left corner first. Type all commands in the text editor. Execute one or several commands by highlighting those commands, holding Ctrl key and hitting Return button. In that way you are preserving your work as a script. You are advised to read help pages for all R functions you will use.
a) Ask the system for the current working directory. On your operating system, create a special directory for work with R, something like C:CodeR or
/code/R. Make that directory both readable and writable.
b) Change your working directory to the new directory using appropriate R function. Copy the attached file Smokers.txt to your new directory.
c) Create a vector vv with elements which repeat numbers 1,2,3 five times, using functions rep() and c(). What is the length of you vector. Do not just tell us, please as R to tell you the length. Save that vector into a file in your working directory using function save(). Initially, name your file vv.RData. Try to open the file with an editor like Vim or notepad. Please do not change anything in the file.
d) Save your vector vv into another file, called vv.txt. This time turn the ascii parameter of save() function to TRUE. Try reading your file. Could you do it this time?
e) Use R function list.files() to list the content of your working directory.
f) Point function list.files() to any other directory and assign its result to a variable. What is the class of that variable? (Hint, use function class()). What is the structure of variable vv. (Hint, use function str()). What is the mode of variable vv. (Hint, use function mode()).
g) Remove variable vv from your workspace. Next, load that variable from file vv.RData. Verify that you got whatever you stored.
h) Remove variable vv from your workspace, again. This time, load that variable from file vv.txt. Again, verify that you have recovered your variable.
i) Save the content of your text editor as a file with extension R. You can rerun all commands in that file as a script, if you want, one day. You might want to edit the file first, but that is another matter. Provide that file as a part of your submission.
j) Close R Studio. Do not forget to save your workspace. Restart R Studio. Convince yourself that all of your variables are there.

Problem 2. Create a vector num of numbers with 8 randomly ordered values between 1 and 20. Use c() function.
a) Turn that vector into another vector of characters cnum using function as.character().
b) Calculate minimum, maximum and mean value of two vectors.
c) Transform vector cnum back into numbers using function as.numeric(). Verify that you got numbers back.
d) Create another vector snum by selecting only those numbers from vector num which are greater than 10.
e) Create a logical vector lnum which will tell you whether an entry in vector cnum is greater than 10.
f) Set 3rd element of vector cnum to NA. Recreate logical vector lnum and report its elements. Recreate vector snum by selecting those elements of vector cnum which are greater than 10. What was the effect of NA.

Problem 3. Create matrix A with 3 rows and 4 columns. Use small integer values between -3 and 3 for elements of matrix A.

a) Create new matrix B obtained by subtracting -1 from all elements of matrix A.
b) Create new matrix C obtained by multiplying by 2 all elements of matrix A.
f) Determine matrix AAT which is an inverse of matrix TAA. Prove that AAT multiplied by TAA produces a unit matrix. Unit matrix has all elements on the diagonal equal to 1 and all other elements equal to 0.

Problem 4. Load data in attached file Smokers.txt into variable smokers using function read.delim(). Use parameters header=TRUE, instructing R to read column header names from the first row of the file, and sep=” ”, telling R that file is tab delimited. As a side note, parameter header=TRUE works only if the first row of the data file has one element fewer than the rest of the file.
a) What are the class, mode and str(ucture) of variable smokers.
b) What are the dimensions of variable smokers.
c) What are the labels (names of horizontal rows) of variable smokers.
d) List values in individual columns of variable smokers.
e) You have noticed that R interpreted column GDPPerCapita as a factor, i.e. a low cardinality column that could be represented by a small number of levels. R made a mistake and we want that column to be a set of integers just like column GDPRank. You can remove factors from column GDPPerCapita by using function droplevels(). Verify that offending factor is gone by redisplaying the structure of variable smokers.
f) Display columns PercentSmokers and GDPPerCapita using bracket notation or [, index] selection.
h) Create a histogram displaying the number of countries in GDPPerCapita brackets 0 to 2,000, 2,000 to 3,000, 3,000 to 5,000, 5,000 to 10,000 and 10,000 to 50,000. Label your histogram. Paint the title in purple color.
i) Present the same histogram as a pie chart.

SUBMISSION INSTRUCTIONS:

Your main submission should be an MS Word document containing your code, results produced by that code and brief textual descriptions of what you did and why. Typically, you just copy your code and results from the R console and past them into the Word document. Start with this text of homework assignment as the template. Please add any other files that you might have used or generated.

Package everything into an archive called E185_LastNameFirstNameHW01.zip. Naming your file properly is important. We download many files and if they are all named Assignment01.zip it becomes hard not to overwrite and lose them. Please do not use archiving tools which do not produce ZIP files.
If you are using a Mac, please make sure that your files are READABLE to users of

If you have issues with the formulation of the assignment or the software you are using, please FIRST go to the Discussion Forum on the class web site: http://isites.harvard.edu/icb/icb.do?keyword=k93720 and check whether someone else raised the same issue and whether the answer is already there. If not, raise the issues yourself. A person from the class or a member of the teaching stuff will respond.

If the issue is not address for a while, please send an inquiry to cscie185@fas.harvard.edu. The discussion forum is a very important tool. We all learn from the discussions on the forum.

If we respond to your inquiry to the class email address, PLEASE DO NOT RESPOND WITH A THANK YOU NOTE. This is not a joke. We will take 2% of your grade for that week’s assignment for every “thank you note”.