Below are a set of excercises to get you practicing with R

A. Practice the analysis pipeline using control statements!

Write a script that completes the following tasks:

Be sure to write your name and the date at the top of the script in a comment

  1. Clear your working environment

  2. Load the data possum_trimmed.csv from D2L.

  3. look at the structure of the possum data using str()

  4. Set the graphing parameters so that you have a 2 row x 4 (use = par(mfrow=c(2,4))) column graphing window (8 graphs total).

  5. Write a for loop that runs through each column of possum except the last one (belly size), checks if that column is numeric, and if so:

  1. plots the relationship between that variable (as x) and belly size (as y),

This is a complicated one, but here is some psuedocode to help you out

# read in the data using read.csv()

# check the structure using str()

# set the graphing window parameters using par() and the mfrow argument

# start the for loop (run it from 1 to 9, which is ncol(possum)-1)

# using an if statement, test if the ith column is numeric

#if the column is numeric, create a plot with the ith column as the x and the last column as the y 

#end the if statement

#end the for loop

B. More practice with for loops

Using the built in data set USPersonalExpenditure write for loop that takes the mean amount spent on each category from 1940-1960. Use the result to make a barplot of the mean expenditures for each category.

hints: First create an empty vector named uspe.means (use= uspe.means <- vector()). In the for loop, populate the vector with the means of each category, AND name each vector element using ‘names(uspe.means)’. Then use barplot() to make the graphic.

C. Writing your own functions

Write a function which:

Takes a file name and two numbers (the defaults for the two numbers should be 1 and 2)

Reads in a table of data (assume that the file is comma delimited)

Plots the columns represented by the two numbers against each other

*Hints: Use the read.csv() function Use print() to check the values of intermediate results (to see if your function is working) Use the test file ”primates.csv" to check your program.