MetroCard Graph

mtafares.R

##  Side project name: Refilling MTA cards (March 2015 rates)
##  Author: Mathew Kiang
##  See: http://mathewkiang.com/2015/03/23/new-metrocard-rates-and-the-dreaded-dead-zone-of-change/
library(ggplot2)

##  Define parameters
price <- 2.75
bonus <- 1.11
lim   <- 0.15   # amount of change willing to tolerate
upp   <- 25     # upper limit to amount deposited
intvl <- 0.05   # intervals the MTA machines allow you to deposit

##  Define how much you spend and what it's worth
spend <- seq(5, upp, by = intvl)
worth <- round(spend * bonus, 3)
rides <- floor(worth / price)

##  Calculate change
left  <- worth %% price

##  Initialize and fill dataframe
mtadf <- data.frame(spend, worth, rides, left)

##  Make a printable variable $$ variable
dolladolla <- paste0('$', sprintf(mtadf$spend[mtadf$left < lim], 
                                  fmt = '%.02f'), ' ($', 
                     sprintf(mtadf$left[mtadf$left < lim], fmt = '%.02f'), ')')
mtadf$exact[mtadf$left < lim] <- dolladolla

##  Take minimum for each ride only -- this only matters if lim > intvl.
mins  <- aggregate(mtadf$spend, by = list(mtadf$rides), FUN = min)$x
mtadf$exact[!(mtadf$spend %in% mins)] <- NA

##  Plot
p <- ggplot(data = mtadf, 
            aes(x = spend, y = rides, color = left)) + 
    geom_point() + 
    theme_classic() + 
    geom_text(aes(label = exact, x = spend - .05, y = rides + .2), 
              vjust = 0, hjust = 0) + 
    theme(legend.position = c(1, 0), 
          legend.justification = c(1, 0)) + 
    scale_color_gradient(name = 'Remaining balance\n(aka "dead zone")', 
                         limits = c(0, 3), 
                         labels = c("$0", "$1", "$2", "$3"), 
                         breaks = 0:3) + 
    scale_y_discrete(breaks = seq(0, 11, by = 2)) + 
    scale_x_continuous(breaks = seq(0, 30, by = 5), 
                       limit = c(4.9, 27.5), 
                       expand = c(.01, 0)) + 
    labs(x = "Amount Added to Card ($)", 
         y = "# of Rides", 
         title = "Optimal MetroCard Refilling by Number of Rides")

ggsave(p, file = './mtafares.jpg', width = 5, height = 2, scale = 2.4)