Lab 02

Due Jan 31 5:00 PM PST

Instructions

For this homework, provide a rendered R Markdown file in PDF format. You may render the R Markdown file to HTML and then convert the HTML file to PDF using the print function in a web browser. Indicate your student number on the markdown file and make a section for each problem.

Problem 1: My Median

1. Write an R function called my_median. This function should take a single parameter (a vector) and return the median of that vector. Write this function without using the built-in R command median. Provide the code for this function.

(4 points)

# Example R code
define_my_median <- function(vector) {
  # Code logic here
  return(quantile(vector, probs = 0.5, na.rm = TRUE))
}

2. Consider the stock prices in the file AS-N100.tsv provided in the archive for week 3. These data involve stock prices for 27 symbols (in the column ticker). Compute your student number modulo 27 and add one, call this value a (i.e., a is a number between 1 and 27 inclusive). Imagine a list of the 27 symbols in alphabetical order. You will examine the a-th symbol in this list. You may find the symbol using the R code sort(unique(data$ticker))[a]. Compute the median opening price of the symbol you examine over all rows in AS-N100.tsv involving that symbol, using your my_median function. Provide all code and output.

(2 points)

## this code doesn't run at the moment, need to modify it


# Example R code to read and process
library(readr)
data <- read_tsv("AS-N100.tsv", show_col_types = FALSE)
symbols <- sort(unique(data$ticker))

# Compute value of 'a'
a <- (301623300 %% 27) + 1
a

symbols <- sort(unique(data$ticker))[a]

# Example of custom median application

my_median <- define_my_median(subset(data, ticker == symbols)$open)
my_median

---

Problem 2: X Marks the Spot

1. The image Figure03.png (provided in the archive containing this lab) is a satellite photo of Vancouver and the surrounding area. In this problem, you will mark the location of a library on this image automatically using code.

The upper left-hand corner of this image has approximate GPS coordinates 49.410705,-124.217671. The lower right-hand corner of this image has approximate GPS coordinates 47.929083,-121.994887. Consider the file libraries.json provided in the archive for week 3. This file contains information about 21 branches of the Vancouver Public Library.

Write R code to display Figure03.png and to mark an X symbol on the GPS coordinates of the b-th library branch. Print the name and address of the library branch directly below the X. Here, b is your student number modulo 21 plus one (i.e., b is a number between 1 and 21 inclusive).

Note that after loading the library rjson and loading libraries.json using:

libraries <- fromJSON(file = "libraries.json")

the coordinates of the b-th branch can be accessed with:

libraries[["features"]][[b]][["geometry"]]$coordinates

The branch name and address can be accessed with:

libraries[["features"]][[b]][["properties"]]$maptip

Provide your code and the resulting display.

(4 points)

## this code doesn't run at the moment, need to modify it

# Example R code for the library plot
library(rjson)
library(imager)
library(ggplot2)
library(png)
library(grid)

libraries <- fromJSON(file = "libraries.json")
# Additional code to process and display

b <- (301623300 %% 21) + 1
b

coordinates <- libraries[["features"]][[b]][["geometry"]]$coordinates
maptip <- libraries[["features"]][[b]][["properties"]]$maptip

upper_left <- c(49.410705, -124.217671)
lower_right <- c(47.929083, -121.994887)

img_width <- 8094
img_height <- 8094

x_pixel <- img_width * (coordinates[1] - upper_left[2]) / (lower_right[2] - upper_left[2])
y_pixel <- img_height * (upper_left[1] - coordinates[2]) / (upper_left[1] - lower_right[1])


image <- load.image("Figure03.png")

plot <- ggplot() +
  annotation_custom(rasterGrob(image, width = unit(1, "npc"), height = unit(1, "npc")))+
  geom_point(aes(x = x_pixel, y = y_pixel), color = "red", size = 3) +
  annotate("text", x = x_pixel, y = y_pixel - 20, label = maptip, color = "blue", size = 4, hjust = 0.5) +
  xlim(0, img_width) +
  ylim(0, img_height) +
  theme_void()

print(plot)