title: How do I plot multiple columns of a dataframe in ggplot?
body: <p>I'm trying to plot a data frame that has "Date" as the x-axis, and stock price as the y-axis, and I have four different stocks to be plotted. I'm very confused by the ggplot documentation, and haven't found an easy solution to this. Here is the data frame:</p>
  
  <pre><code>appleData &lt;- read.csv("AAPL.csv", header = TRUE)
  microsoftData &lt;- read.csv("MSFT.csv", header = TRUE)
  googleData &lt;- read.csv("GOOG.csv", header = TRUE)
  amazonData &lt;- read.csv("AMZN.csv", header = TRUE)
  
  names(appleData) &lt;- c("Date", "AAPL")
  names(microsoftData) &lt;- c("Date", "MSFT")
  names(googleData) &lt;- c("Date", "GOOG")
  names(amazonData) &lt;- c("Date", "AMZN")
  
  mergedData1 &lt;- merge(appleData, microsoftData, by = "Date")
  mergedData2 &lt;- merge(googleData, amazonData, by = "Date")
  totalData &lt;- merge(mergedData1, mergedData2, by = "Date")
  totalData
  </code></pre>
  
  <p>The dataframe is called "totalData", and when I use ggplot(totalData) I get a blank plot. What I need help with specifically is plotting all four stocks onto the same plot, and also rescaling the prices so that they all begin at $100 (so they are on the same scale). Thank you in advance. </p>