library(dplyr)
library(pipeR)

wugo1.tt <- data.frame(station = c("瑞豐站", "武慶三路", "五塊厝", "三信家商",
                                   "五權國小", "林德官(三和市場)", "光華路口(光華夜市)",
                                   "三多市場", "新光三越(捷運三多商)"),
                       wugo1.diff = c(4, 6, 8, 8, 6, 5, 5, 4, 4),
                       row.names = c(31, 21, 10, 5, 11, 20, 15, 3, 30),
                       stringsAsFactors = FALSE)

wugo1.std <- data.frame(station = c("瑞豐站", "永豐路口", "崗山市場", "崗山北街口",
                                    "鐵路機料廠", "鳳山工業區(監理所後)",
                                    "鐵路機廠", "武慶三路", "五塊厝"),
                        time = c("2017/2/15 16:45", "2017/2/15 16:47",
                                 "2017/2/15 16:48", "2017/2/15 16:49",
                                 "2017/2/15 16:50", "2017/2/15 16:51",
                                 "2017/2/15 16:53", "2017/2/15 16:54",
                                 "2017/2/15 16:57"),
                        stringsAsFactors = FALSE)

wugo1.final <- wugo1.std %>>%
    # sort firstly
    arrange(time, station) %>>%
    mutate(rn = 1:n()) %>>%
    (~ xticks <- setNames(.$rn, .$station)) %>>%
    # left join with wugo1.tt
    left_join(wugo1.tt, by = "station") %>>%
    select(rn, station, wugo1.diff)

with(wugo1.final,
     {
         plot(x = rn, y = wugo1.diff, xaxt = "n", xlab = "Station")
         axis(side = 1, at = xticks, labels = names(xticks))
     })