title: How to add a title to each plot in R?
body: <p>This code will show several plots on one window. As each plot was produced according  to each column named X1 to X13 . SO I want to add <code>as a main</code> to each figure the name of the column used to plot the figure see below to distinguish which is which<img src="https://i.stack.imgur.com/AZHJj.jpg" alt="enter image description here">. </p>
  
  <pre><code>ref= read.table("D:\\AS_asc.txt", sep="",header=TRUE)
  sour1 = read.table("D:\\re.txt", sep="",header=TRUE) 
  sour2= read.table("D:\\_asc.txt", sep="",header=TRUE)
  columns &lt;- paste0("X", 1:13)
  par(mfrow=c(4,4))
   lapply(
   columns,
   function(column)
    {
     result1 &lt;- (
      mean(ref[[column]]) - 
       ((sd(ref[[column]]) / sd(sour1[[column]])) * mean(sour1[[column]])) + 
       ((sd(ref[[column]]) / sd(sour1[[column]]) * sour1[[column]]))
       )   # calculate using ref and sour1
       result2 &lt;- ((  
        mean(ref[[column]]) - 
        ((sd(ref[[column]]) / sd(sour2[[column]], na.rm=TRUE)) * mean(sour2[[column]], na.rm=TRUE)) + 
       ((sd(ref[[column]]) / sd(sour2[[column]], na.rm=TRUE) * sour2[[column]])) 
      ))  # calculate using ref and sour2
        plot(
      ref[[column]],
      result1,
      ylab = "[[column]]",
      xlab = "[[column]]",
     col  = 2
      )
  
     points(ref[[column]], ref[[column]], col = 'green')
    points(ref[[column]], result2, col = 'blue')
     }
     )
  </code></pre>