title: ggplot2 not displaying values of the Y axis
body: <p>I try to get the values showing of the Y axis but it seems like I can't figure out the issue, here's my code and the results of the plot besides the data:</p>
  
  <pre><code>library(ggplot2)
  
  traffic.data &lt;- structure(list(years = 2008:2017, units = structure(c(1L, 2L, 4L, 5L, 3L, 6L, 7L, 8L, 9L, 10L), .Label = c("12,866,461", "13,350,011", "15,106,666", "15,361,841", "15,669,918", "16,498,204", "17,296,885", "17,611,762", "18,239,288", "20,359,883"), class = "factor")), .Names = c("years", "units"), class = "data.frame", row.names = c(NA, -10L))
  
  traffic.data
         years     units
  #  1   2008 12,866,461
  #  2   2009 13,350,011
  #  3   2010 15,361,841
  #  4   2011 15,669,918
  #  5   2012 15,106,666
  #  6   2013 16,498,204
  #  7   2014 17,296,885
  #  8   2015 17,611,762
  #  9   2016 18,239,288
  # 10  2017  20,359,883
  
  ggplot(traffic.data, aes(x = years, y = as.numeric(units))) + 
     geom_point() +
     geom_line() +
     scale_x_continuous(breaks = seq(2008, 2017, 1)) + 
     scale_y_continuous(breaks = seq(10000000,30000000,1)) +
     labs(x = "years", y = "total traffic of passengers", 
          title = "evolution of traffic during the past 10 years")
  </code></pre>
  
  <p>When I ran this code I get the following line chart missing the values of Y axis :
  <a href="https://i.stack.imgur.com/8FAmO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8FAmO.png" alt="the R plot results"></a></p>