title: Plotting large number of time series using ggplot. Is it possible to speed up?
body: <p>I am working with thousands of meteorological time series data (Sample data can be downloaded from here)
  <a href="https://dl.dropboxusercontent.com/s/bxioonfzqa4np6y/timeSeries.txt" rel="nofollow noreferrer">https://dl.dropboxusercontent.com/s/bxioonfzqa4np6y/timeSeries.txt</a></p>
  
  <p>Plotting these data using ggplot2 on my Linux Mint PC (64bit, 8GB RAM, Dual-core 2.6 GHz) took a lot of time. I'm wondering if there is a way to speed it up or a better way to plot these data? Thank you very much in advance for any suggestion!</p>
  
  <p>This is the code I'm using for now</p>
  
  <pre><code>##############################################################################
  #### load required libraries
  library(RCurl)
  library(reshape2)
  library(dplyr)
  library(ggplot2)
  
  ##############################################################################
  #### Read data from URL
  dataURL &lt;- "https://dl.dropboxusercontent.com/s/bxioonfzqa4np6y/timeSeries.txt"
  tmp &lt;- getURL(dataURL)
  df &lt;- tbl_df(read.table(text = tmp, header = TRUE))
  df
  
  ##############################################################################
  #### Plot time series using ggplot2
  # Melt the data by date first
  df_melt &lt;- melt(df, id = "date")
  str(df_melt)
  
  df_plot &lt;- ggplot(data = df_melt, aes(x = date, y = value, color = variable)) +
    geom_point() +
    scale_colour_discrete("Station #") +
    xlab("Date") +
    ylab("Daily Precipitation [mm]") +
    ggtitle("Daily precipitation from 1915 to 2011") +
    theme(plot.title = element_text(size = 16, face = "bold", vjust = 2)) + # Change size &amp; distance of the title
    theme(axis.text.x = element_text(angle = 0, size = 12, vjust = 0.5)) + # Change size of tick text
    theme(axis.text.y = element_text(angle = 0, size = 12, vjust = 0.5)) +
    theme( # Move x- &amp; y-axis lables away from the axises
      axis.title.x = element_text(size = 14, color = "black", vjust = -0.35),
      axis.title.y = element_text(size = 14, color = "black", vjust = 0.35)) +
    theme(legend.title = element_text(colour = "chocolate", size = 14, face = "bold")) + # Change Legend text size
    guides(colour = guide_legend(override.aes = list(size = 4))) + # Change legend symbol size
    guides(fill = guide_legend(ncols = 2))
  df_plot
  </code></pre>