ECO 395M: Exercises 1

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1) Data visualization: flights at ABIA

This problem involves data exploration and data visualization using `ggplot2` and the `tidyverse`, but is entirely open-ended. Recall these lessons from ECO s394D and revisit those notes and walkthroughs as needed.

Consider the data in [ABIA.csv](ABIA.csv), which contains information on every commercial flight in 2008 that either departed from or landed at Austin-Bergstrom Interational Airport. The variable codebook is as follows:

– Year all 2008
– Month 1-12
– DayofMonth 1-31
– DayOfWeek 1 (Monday) – 7 (Sunday)
– DepTime actual departure time (local, hhmm)
– CRSDepTime scheduled departure time (local, hhmm)
– ArrTime actual arrival time (local, hhmm)
– CRSArrTime scheduled arrival time (local, hhmm)
– UniqueCarrier unique carrier code
– FlightNum flight number
– TailNum plane tail number
– ActualElapsedTime in minutes
– CRSElapsedTime in minutes
– AirTime in minutes
– ArrDelay arrival delay, in minutes
– DepDelay departure delay, in minutes
– Origin origin IATA airport code
– Dest destination IATA airport code
– Distance in miles
– TaxiIn taxi in time, in minutes
– TaxiOut taxi out time in minutes
– Cancelled was the flight cancelled?
– CancellationCode reason for cancellation (A = carrier, B = weather, C = NAS, D = security)
– Diverted 1 = yes, 0 = no
– CarrierDelay in minutes
– WeatherDelay in minutes
– NASDelay in minutes
– SecurityDelay in minutes
– LateAircraftDelay in minutes

Your task is to create a figure, or set of related figures, that tell an interesting story about flights into and out of Austin. You should annotate your figure(s), of course, but strive to make them as easy to understand as possible at a quick glance. (A single figure shouldn’t need many, many paragraphs to convey its meaning.) For example, you might consider one of the following questions:

– What is the best time of day to fly to minimize delays, and does this change by airline?
– What is the best time of year to fly to minimize delays, and does this change by destination? (You’d probably want to focus on a handful of popular destinations.)
– How do patterns of flights to different destinations or parts of the country change over the course of the year?
– What are the bad airports to fly to and does this change by time of year or day?

But anything interesting will fly :-). If you want to try your hand at mapping or looking at geography, you can cross-reference the airport codes here: [https://github.com/datasets/airport-codes](https://github.com/datasets/airport-codes). Combine this with a mapping package like ggmap, and you should have lots of possibilities!

2) Wrangling the Olympics

The data in [olympics_top20.csv](olympics_top20.csv) contains information on every Olympic medalist in the top 20 sports by participant count, all the way back to 1896. Use these data to answer the following questions. (The names of the columns should be self-explanatory.)

A) What is the 95th percentile of heights for female competitors across all Athletics events (i.e., track and field)? Note that `sport` is the broad sport (e.g. Athletics) whereas `event` is the specific event (e.g. 100 meter sprint).

B) Which single women’s `event` had the greatest variability in competitor’s heights across the entire history of the Olympics, as measured by the standard deviation?

C) How has the average age of Olympic swimmers changed over time? Does the trend look different for male swimmers relative to female swimmers? Create a data frame that can allow you to visualize these trends over time, then plot the data with a line graph with separate lines for male and female competitors. Give the plot an informative caption answering the two questions just posed.

3) K-nearest neighbors: cars

The data in [sclass.csv](sclass.csv) contains data on over 29,000 Mercedes S Class vehicles—essentially every such car in this class that was advertised on the secondary automobile market during 2014. For websites like Cars.com or Truecar that aim to provide market-based pricing information to consumers, the Mercedes S class is a notoriously difficult case.

There is a huge range of sub-models that are all labeled “S Class,”” from large luxury sedans to high-performance sports cars; one sub-category of S class has even served as the safety car in Formula 1 Races. Moreover, individual submodels involve cars with many different features. This extreme diversity—unusual for a single model of car—makes it difficult to provide accurate pricing predictions to consumers.

We’ll revisit this data set later in the semester when we’ve got a larger toolkit for building predictive models. For now, let’s focus on three variables in particular:
– trim: categorical variable for car’s trim level, e.g. 350, 63 AMG, etc. The trim is like a sub-model designation.
– mileage: mileage on the car
– price: the sales price in dollars of the car

Your goal is to use K-nearest neighbors to build a predictive model for price, given mileage, separately for each of two trim levels: 350 and 65 AMG. (There are lots of other trim levels that you’ll be ignoring for this question.) That is, you’ll be treating the 350’s and the 65 AMG’s as two separate data sets. (Recall the `filter` command.)

For each of these two trim levels:
1) Split the data into a training and a testing set.
2) Run K-nearest-neighbors, for many different values of K, starting at K=2 and going as high as you need to. For each value of K, fit the model to the training set and make predictions on your test set.
3) Calculate the out-of-sample root mean-squared error (RMSE) for each value of K.

For each trim, make a plot of RMSE versus K, so that we can see where it bottoms out. Then for the optimal value of K, show a plot of the fitted model, i.e. predictions vs. x. (Again, separately for each of the two trim levels.)

Which trim yields a larger optimal value of K? Why do you think this is?