dplyr

• What is the difference between read_xls() and read_xlsx() functions? What message do you get if reading an .xlsx file using read_xls() function?

• What does the skip argument do?

• Do we need to refer to a sheet within an excel file as a number, or can we refer to it as the sheet name instead?

• What does the guess_max argument do?

• What happens if columns in the Excel worksheet are of different length?

• How would you write into an Excel file? Demonstrate saving the mtcars dataset into an Excel file.

• Use the starwars dataset that is loaded with the tidyverse. Accomplish the following in one long string of pipes.

  • Keep only observations with weight and height recorded. Also include the homeworld variable.
  • Create a variable called bmi that calculates the character’s BMI (search for formula).
  • Summarize the BMI variable, grouping observations by homeworld.
  • Print this summary in decreasing order of average BMI.

• Read in the following data into R. This data is from the American Community Survey and references the population of three cities in Virginia between 2009 and 2012. cities <- data.frame(name = rep(c("richmond", "norfolk", "charlottesville")), pop2009 = c(1202494,236071,191515), pop2010 = c(1235565,242143,197279), pop2011 = c(1248271,241943,199675), pop2012 = c(1260202,243056,210909)) In one long string of pipes, convert the data from wide (2009 to 2012 population values) to long format, naming the new column of populations pop, group by city, create a summary variable that is the ratio of the largest population value to smallest population value for the city, and arrange by this ratio value in decreasing order.